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Physics · Electric Current

Flip through 20 full sample pages with substantial teaching notes, deep-dive explanations, worked practice, exam application and self-check questions.

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Overview

Electricity: a complete revision map

This sample moves from the meaning of current and charge through potential difference, resistance, circuit rules, power and energy. The aim is not simply to memorise equations, but to recognise which physical quantity a question is describing and to select an equation with the correct SI units.

  • Current links charge to time.
  • Potential difference links energy to charge.
  • Resistance links potential difference to current.
  • Series and parallel circuits obey different current and voltage rules.
Worked example / practice: Quick diagnostic: if 12 C of charge passes a point in 3.0 s, the current is 4.0 A because I = Q/t = 12/3.

Deep-dive notes

The central idea on this page is electricity: a complete revision map. To use it confidently, connect the definition or rule above to the specific details listed here: Current links charge to time.; Potential difference links energy to charge.; Resistance links potential difference to current.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Electricity: a complete revision map” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain electricity: a complete revision map without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Before calculating, write the quantity, symbol and SI unit beside every number in the question.
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Core definition

Electric current

Electric current is the rate of flow of electric charge. In a metallic conductor the mobile charge carriers are electrons, while conventional current is defined in the direction positive charge would move. The conventional-current direction is therefore opposite to electron drift in a metal.

  • Equation: I = Q/t.
  • I in amperes (A), Q in coulombs (C), t in seconds (s).
  • 1 A means 1 C of charge passes a point each second.
  • An ammeter is connected in series with the component.
Worked example / practice: Worked example: 45 C passes through a lamp in 15 s. I = 45/15 = 3.0 A.

Deep-dive notes

The central idea on this page is electric current. To use it confidently, connect the definition or rule above to the specific details listed here: Equation: I = Q/t.; I in amperes (A), Q in coulombs (C), t in seconds (s).; 1 A means 1 C of charge passes a point each second.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Electric current” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain electric current without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Do not define current as 'the amount of charge'. The phrase rate of flow is essential.
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Charge

Charge, electrons and current direction

Charge is measured in coulombs. An electron carries a negative elementary charge, so an enormous number of electrons correspond to even a small macroscopic charge. Circuit diagrams normally use conventional current direction because this convention was established before the electron was discovered.

  • Charge is conserved in ordinary circuit processes.
  • Electrons are not 'used up' by a resistor.
  • A resistor transfers electrical energy; it does not consume charge.
  • In a steady series circuit, charge does not pile up at a component.
Worked example / practice: Reasoning check: if 2 A enters a resistor in a simple series circuit, 2 A leaves it. Charge conservation prevents a different steady current leaving.

Deep-dive notes

The central idea on this page is charge, electrons and current direction. To use it confidently, connect the definition or rule above to the specific details listed here: Charge is conserved in ordinary circuit processes.; Electrons are not 'used up' by a resistor.; A resistor transfers electrical energy; it does not consume charge.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Charge, electrons and current direction” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain charge, electrons and current direction without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Questions about 'what is used up' usually test the distinction between charge and energy.
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Equation skills

Using I = Q/t confidently

The current equation is often embedded in multi-step questions. Convert minutes or milliseconds to seconds before substitution, and rearrange symbolically before inserting numbers. A clean rearrangement reduces calculator and unit errors.

  • Q = It when charge is required.
  • t = Q/I when time is required.
  • Convert mA to A by dividing by 1000.
  • Convert minutes to seconds by multiplying by 60.
Worked example / practice: Worked example: a 250 mA current flows for 4 min. I = 0.250 A and t = 240 s, so Q = It = 60 C.

Deep-dive notes

The central idea on this page is using i = q/t confidently. To use it confidently, connect the definition or rule above to the specific details listed here: Q = It when charge is required.; t = Q/I when time is required.; Convert mA to A by dividing by 1000.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Using I = Q/t confidently” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain using i = q/t confidently without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Put the conversion on its own line. Examiners can then follow your method even if the final arithmetic slips.
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Potential difference

Potential difference and energy transfer

Potential difference measures the energy transferred per unit charge between two points. A cell supplies energy to charge; a component transfers electrical energy into other forms such as thermal energy, light or kinetic energy.

  • Equation: V = W/Q.
  • V in volts (V), W in joules (J), Q in coulombs (C).
  • 1 V = 1 J C⁻¹.
  • A voltmeter is connected in parallel across a component.
Worked example / practice: Worked example: 24 J is transferred when 6 C passes through a component. V = 24/6 = 4 V.

Deep-dive notes

The central idea on this page is potential difference and energy transfer. To use it confidently, connect the definition or rule above to the specific details listed here: Equation: V = W/Q.; V in volts (V), W in joules (J), Q in coulombs (C).; 1 V = 1 J C⁻¹.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Potential difference and energy transfer” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain potential difference and energy transfer without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Use 'energy transferred per unit charge' rather than saying voltage is simply 'the force pushing electrons'.
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Resistance

Resistance and Ohm's law

Resistance describes how strongly a component opposes current for a given potential difference. For an ohmic conductor at constant temperature, current is directly proportional to potential difference, so resistance remains constant.

  • Equation: R = V/I.
  • Resistance is measured in ohms (Ω).
  • For an ohmic resistor, a V–I graph through the origin has constant gradient V/I.
  • Temperature must be constant for the simple Ohm's-law statement.
Worked example / practice: Worked example: a resistor has 9.0 V across it and carries 0.30 A. R = 9.0/0.30 = 30 Ω.

Deep-dive notes

The central idea on this page is resistance and ohm's law. To use it confidently, connect the definition or rule above to the specific details listed here: Equation: R = V/I.; Resistance is measured in ohms (Ω).; For an ohmic resistor, a V–I graph through the origin has constant gradient V/I.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Resistance and Ohm's law” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain resistance and ohm's law without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: If the component heats up, do not automatically assume resistance remains constant.
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I–V characteristics

Reading component graphs

Different components have different current–voltage characteristics because their resistance may change with temperature, light or applied voltage. Graph questions reward careful reference to slope or curvature rather than vague statements.

  • Fixed resistor at constant temperature: straight line through origin.
  • Filament lamp: curve becomes less steep as temperature rises and resistance increases.
  • Diode: very small current in reverse bias and below forward threshold; current then rises rapidly.
  • An LDR is described by resistance versus light, not a simple ohmic I–V rule.
Worked example / practice: Interpretation: if a filament lamp's V/I value increases as current increases, its resistance is rising because the filament becomes hotter.

Deep-dive notes

The central idea on this page is reading component graphs. To use it confidently, connect the definition or rule above to the specific details listed here: Fixed resistor at constant temperature: straight line through origin.; Filament lamp: curve becomes less steep as temperature rises and resistance increases.; Diode: very small current in reverse bias and below forward threshold; current then rises rapidly.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Reading component graphs” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain reading component graphs without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: State both the observed graph change and the physical reason.
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Series circuits

Series circuit rules

A series circuit has one current path. The same current passes through every component. The supply potential difference is shared between components, and the total resistance is the sum of individual resistances.

  • I₁ = I₂ = I₃ in one series path.
  • V_supply = V₁ + V₂ + ...
  • R_total = R₁ + R₂ + ...
  • Adding a series resistor increases total resistance and usually reduces current for a fixed supply.
Worked example / practice: Worked example: 4 Ω and 8 Ω resistors in series give R_total = 12 Ω. With 6 V, I = 6/12 = 0.50 A.

Deep-dive notes

The central idea on this page is series circuit rules. To use it confidently, connect the definition or rule above to the specific details listed here: I₁ = I₂ = I₃ in one series path.; V_supply = V₁ + V₂ + ...; R_total = R₁ + R₂ + .... These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Series circuit rules” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain series circuit rules without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: When asked why current is equal in series, connect the explanation to charge conservation.
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Parallel circuits

Parallel circuit rules

Parallel branches connect across the same two points, so every branch has the same potential difference. Current splits at junctions according to branch resistance and recombines afterwards.

  • V is the same across parallel branches.
  • I_total = I₁ + I₂ + ... at a junction.
  • Adding another parallel branch reduces the equivalent resistance.
  • Lower-resistance branches generally carry larger current at the same voltage.
Worked example / practice: Example: if the total current is 5 A and one branch carries 2 A, the other branch carries 3 A.

Deep-dive notes

The central idea on this page is parallel circuit rules. To use it confidently, connect the definition or rule above to the specific details listed here: V is the same across parallel branches.; I_total = I₁ + I₂ + ... at a junction.; Adding another parallel branch reduces the equivalent resistance.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Parallel circuit rules” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain parallel circuit rules without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Draw arrows at junctions and apply current conservation explicitly.
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Power

Electrical power

Power is the rate at which energy is transferred. In circuits, electrical power can be calculated from potential difference and current, with alternative forms obtained by substituting Ohm's law for ohmic components.

  • P = VI.
  • For an ohmic resistor: P = I²R and P = V²/R.
  • Power is measured in watts (W).
  • 1 W = 1 J s⁻¹.
Worked example / practice: Worked example: a heater connected to 230 V draws 4.0 A. P = 230 × 4.0 = 920 W.

Deep-dive notes

The central idea on this page is electrical power. To use it confidently, connect the definition or rule above to the specific details listed here: P = VI.; For an ohmic resistor: P = I²R and P = V²/R.; Power is measured in watts (W).. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Electrical power” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain electrical power without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Choose the power equation that uses the quantities directly given rather than creating extra calculation steps.
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Energy

Electrical energy and cost

Electrical energy transferred is power multiplied by time. In physics calculations use joules with time in seconds; domestic electricity bills commonly use kilowatt-hours, where energy in kWh equals power in kW multiplied by time in hours.

  • E = Pt and E = VIt.
  • 1 kWh = 3.6 × 10⁶ J.
  • Convert watts to kilowatts by dividing by 1000.
  • Cost = energy used in kWh × tariff per kWh.
Worked example / practice: Example: a 2.0 kW heater runs for 1.5 h. Energy = 3.0 kWh. At €0.25/kWh, cost = €0.75.

Deep-dive notes

The central idea on this page is electrical energy and cost. To use it confidently, connect the definition or rule above to the specific details listed here: E = Pt and E = VIt.; 1 kWh = 3.6 × 10⁶ J.; Convert watts to kilowatts by dividing by 1000.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Electrical energy and cost” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain electrical energy and cost without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Do not mix W with hours if the answer is required in joules.
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Sensors

LDRs and thermistors

Sensor circuits use components whose resistance changes with environmental conditions. An LDR's resistance typically decreases as light intensity increases. An NTC thermistor's resistance decreases as temperature increases.

  • LDR: brighter light → lower resistance.
  • NTC thermistor: higher temperature → lower resistance.
  • Potential-divider circuits convert resistance changes into voltage changes.
  • Always identify where the output voltage is measured.
Worked example / practice: Reasoning: in a two-resistor potential divider, increasing the resistance of the lower resistor increases the voltage measured across that lower resistor.

Deep-dive notes

The central idea on this page is ldrs and thermistors. To use it confidently, connect the definition or rule above to the specific details listed here: LDR: brighter light → lower resistance.; NTC thermistor: higher temperature → lower resistance.; Potential-divider circuits convert resistance changes into voltage changes.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “LDRs and thermistors” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain ldrs and thermistors without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Potential-divider questions depend on component position. Sketch the circuit before predicting the output.
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Inductors

Self-induction and changing current

An inductor opposes changes in current because a changing current produces a changing magnetic field and therefore an induced emf. By Lenz's law, the induced emf acts in the direction that opposes the change producing it.

  • Induced emf magnitude: ε = L|dI/dt|.
  • L is inductance in henries (H).
  • When current rises, the induced emf opposes the supply.
  • At steady DC, dI/dt = 0, so the induced emf falls to zero.
Worked example / practice: Example: for L = 0.10 H and dI/dt = 80 A s⁻¹, |ε| = 8.0 V.

Deep-dive notes

The central idea on this page is self-induction and changing current. To use it confidently, connect the definition or rule above to the specific details listed here: Induced emf magnitude: ε = L|dI/dt|.; L is inductance in henries (H).; When current rises, the induced emf opposes the supply.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Self-induction and changing current” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain self-induction and changing current without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Link Lenz's law to conservation of energy: the induced effect cannot reinforce the change without an external energy source.
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Measurement

Meters and practical circuits

Correct meter placement is a frequent source of lost marks. An ammeter measures current through a component and is placed in series. A voltmeter measures potential difference between two points and is connected in parallel.

  • Ideal ammeter: very low resistance.
  • Ideal voltmeter: very high resistance.
  • Check range and zero before reading analogue instruments.
  • Repeat readings and control variables in practical work.
Worked example / practice: Practical plan: vary the potential difference across a resistor, record V and I pairs, and plot V against I to determine resistance from the gradient if temperature is controlled.

Deep-dive notes

The central idea on this page is meters and practical circuits. To use it confidently, connect the definition or rule above to the specific details listed here: Ideal ammeter: very low resistance.; Ideal voltmeter: very high resistance.; Check range and zero before reading analogue instruments.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Meters and practical circuits” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain meters and practical circuits without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Always state what is varied, what is measured, what is controlled and how the data are processed.
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Uncertainty

Measurements, graphs and uncertainty

Experimental questions often test data quality as much as circuit theory. Repeat measurements, use an appropriate range, plot a large graph and use a best-fit line or curve rather than joining dots mechanically.

  • Record units in table headings.
  • Use sensible significant figures consistent with instrument resolution.
  • A best-fit line represents the overall trend.
  • Gradient calculations should use a large triangle.
Worked example / practice: If V = 5.00 V and I = 0.42 A, report R to a sensible precision rather than many calculator digits.

Deep-dive notes

The central idea on this page is measurements, graphs and uncertainty. To use it confidently, connect the definition or rule above to the specific details listed here: Record units in table headings.; Use sensible significant figures consistent with instrument resolution.; A best-fit line represents the overall trend.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Measurements, graphs and uncertainty” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain measurements, graphs and uncertainty without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Do not write 'human error'. Name the actual source: reading resolution, contact resistance, heating or timing uncertainty.
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Multi-step problem

Combining equations

Harder questions combine current, resistance, power and energy. The safest method is to write the target quantity, list the information given, identify an intermediate quantity if necessary, and keep unrounded values until the final answer.

  • Step 1: write known quantities with units.
  • Step 2: choose the relationship that directly connects them.
  • Step 3: calculate intermediate values.
  • Step 4: check dimensions and physical plausibility.
Worked example / practice: Example: a 12 V device of resistance 6 Ω operates for 5 min. I = 2 A, P = 24 W, t = 300 s, so E = 7200 J.

Deep-dive notes

The central idea on this page is combining equations. To use it confidently, connect the definition or rule above to the specific details listed here: Step 1: write known quantities with units.; Step 2: choose the relationship that directly connects them.; Step 3: calculate intermediate values.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Combining equations” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain combining equations without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: A structured chain of equations earns method credit and makes mistakes easier to spot.
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Exam language

How to answer 'explain' questions

A calculation can be correct but an explanation can still lose marks if it only states a fact. Build explanations as cause → mechanism → consequence. Use the quantities named in the question.

  • Describe: state what happens.
  • Explain: give the physical reason.
  • Compare: refer to both cases.
  • Evaluate: use evidence and limitations before a judgement.
Worked example / practice: Model explanation: 'The filament becomes hotter as current increases. Increased lattice vibration causes more collisions with electrons, so resistance increases and the I–V graph curves.'

Deep-dive notes

The central idea on this page is how to answer 'explain' questions. To use it confidently, connect the definition or rule above to the specific details listed here: Describe: state what happens.; Explain: give the physical reason.; Compare: refer to both cases.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “How to answer 'explain' questions” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain how to answer 'explain' questions without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Avoid circular explanations such as 'resistance increases because it has more resistance'.
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Common errors

Electricity misconceptions to eliminate

Many exam errors come from mixing up charge, current, voltage and energy. Treat each as a different physical quantity with its own meaning, unit and measuring instrument.

  • Current is not 'used up'.
  • Voltage is not the same as current.
  • A battery supplies energy; it does not supply a fixed current regardless of circuit.
  • Parallel branches have equal voltage, not necessarily equal current.
Worked example / practice: Self-test: explain in one sentence why two different resistors in parallel can have different currents even though they share the same voltage.

Deep-dive notes

The central idea on this page is electricity misconceptions to eliminate. To use it confidently, connect the definition or rule above to the specific details listed here: Current is not 'used up'.; Voltage is not the same as current.; A battery supplies energy; it does not supply a fixed current regardless of circuit.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Electricity misconceptions to eliminate” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain electricity misconceptions to eliminate without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: If your explanation uses the word 'electricity' repeatedly, replace it with the precise quantity you mean.
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Practice

Exam-style practice set

Try these without looking back. 1) 360 C flows in 2 min: calculate current. 2) A 24 Ω resistor carries 0.50 A: calculate voltage. 3) A 12 V motor draws 3 A for 40 s: calculate energy. 4) Explain why a filament lamp is non-ohmic.

  • Q1: convert 2 min to 120 s.
  • Q2: use V = IR.
  • Q3: P = VI, then E = Pt.
  • Q4: temperature rise changes resistance.
Worked example / practice: Answers: 1) 3.0 A. 2) 12 V. 3) 1440 J. 4) Heating increases lattice vibration and resistance, so I is not directly proportional to V.

Deep-dive notes

The central idea on this page is exam-style practice set. To use it confidently, connect the definition or rule above to the specific details listed here: Q1: convert 2 min to 120 s.; Q2: use V = IR.; Q3: P = VI, then E = Pt.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “Exam-style practice set” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain exam-style practice set without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: After marking, redo any missed question from a blank page rather than merely reading the answer.
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Summary

One-page electricity checklist

You should now be able to define current, potential difference and resistance; use I = Q/t, V = W/Q, V = IR, P = VI and E = Pt; apply series and parallel rules; interpret I–V behaviour; and explain how sensors and inductors respond to changing conditions.

  • Know every symbol and SI unit.
  • Recognise which circuit rule applies before calculating.
  • Show rearrangement and substitution clearly.
  • Use precise physical language in explanations.
Worked example / practice: Final challenge: design a three-step calculation that uses current, power and energy, then solve it and check the units independently.

Deep-dive notes

The central idea on this page is one-page electricity checklist. To use it confidently, connect the definition or rule above to the specific details listed here: Know every symbol and SI unit.; Recognise which circuit rule applies before calculating.; Show rearrangement and substitution clearly.. These are not separate facts to memorise in isolation; they form the reasoning chain you should be able to reconstruct without looking.

A strong revision method is to close the notes after reading this section and reproduce the key idea from memory. Then compare your version with the page, identify any missing terminology, and correct the explanation before moving to practice. This converts passive reading into active retrieval and makes the page useful for both first learning and later revision.

Exam-style application

Possible question: Explain, apply or use the idea of “One-page electricity checklist” in a new situation. Start by stating the relevant rule or definition precisely, then use the information in the question, show the intermediate reasoning, and finish with a conclusion that answers the command word.

  1. Identify exactly what the question is asking and underline the command word.
  2. Write the relevant definition, relationship, rule or principle before substituting or applying it.
  3. Use the information given rather than relying on vague general statements.
  4. Show the reasoning in a logical sequence so method marks remain visible.
  5. Check the final answer for units, terminology, plausibility and relevance to the question.

Before you turn the page

  • Can you define or explain one-page electricity checklist without looking?
  • Can you give one correct example and one common mistake?
  • Can you recognise when this idea should be used in a question?
  • Can you explain your method clearly enough for someone else to follow?
Exam / study tip: Use this preview as a diagnostic. The full resource should deepen weak areas with more examples, questions and worked solutions.
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