Year 7 Physics: Power Voltage and Current in Electric Circuits

Q: How should an ammeter be connected in a circuit to measure current correctly?

Correct Answer: B) In series with the component. Explanation: Ammeters have very low resistance and must be in series so all electric charge flows through them. Mark Scheme: 1 mark for connected in series.

Q: A resistor has a resistance of 10 Ω and a current of 2 A passes through it. What is the potential difference?

Correct Answer: B) 20 V. Explanation: V = I × R = 2 A × 10 Ω = 20 Volts. Mark Scheme: 1 mark for 20 V.

Q: What happens in a series circuit if one bulb breaks?

Correct Answer: B) The circuit is broken and all bulbs go out.. Explanation: A series circuit has only one single continuous path for current. Any break stops the flow entirely. Mark Scheme: 1 mark for all bulbs go out due to open/broken circuit.

Key Learning Objectives

By the end of this lesson and revision module, Year 7 students will be able to:

Understand electric current (rate of flow of charge) and potential difference/voltage (energy transferred per unit charge).
Use standard circuit symbols and differentiate between series and parallel circuits.
Apply Ohm's Law (V = I × R) and Electrical Power formulas (P = I × V).

Topic Summary & Essential Notes

Electricity is the flow of electric charge around a closed conductive circuit. Current (I) is measured in Amperes (A) using an ammeter connected in series. Potential Difference or Voltage (V) is the push that drives electrons, measured in Volts (V) using a voltmeter connected in parallel across components. Resistance (R) opposes charge flow, measured in Ohms (Ω). In a series circuit, current is identical everywhere, but voltage is shared across components. In a parallel circuit, voltage across each branch is equal, and total current splits between branches.

Key Rules, Formulas & Definitions

Ohm's Law Equation

Potential Difference (V) = Current (A) × Resistance (Ω) [V = I × R]

Electrical Power Equation

Power (Watts / W) = Current (A) × Potential Difference (V) [P = I × V]

Series vs Parallel Rules

Series: I_total = I₁ = I₂ | V_total = V₁ + V₂. Parallel: V_total = V₁ = V₂ | I_total = I₁ + I₂

2 Step-by-Step Worked Examples

Study these model solutions to understand how examiners award method and accuracy marks:

Worked Example 1

Worked Example 1: Calculating Resistance Using Ohm's Law

Question: A 12 V battery is connected to a circuit. An ammeter measures a current of 3 A. Calculate the resistance of the circuit.

Step-by-Step Solution:

Step 1: Rearrange Ohm's Law. From V = I × R, we get R = V ÷ I.
Step 2: Insert values. R = 12 V ÷ 3 A.
Step 3: Calculate with units. R = 4 Ohms (4 Ω).

Final Answer: 4 Ω

Senior Examiner Insight: Always write the Greek letter Omega (Ω) or the word 'Ohms' for resistance units.

Worked Example 2

Worked Example 2: Current in a Parallel Circuit

Question: A power pack supplies 6 A of current to a parallel circuit with two identical lamps. Calculate the current passing through each individual lamp.

Step-by-Step Solution:

Step 1: Recall parallel current rule. Total current splits equally among identical parallel branches: I_branch = I_total ÷ number of branches.
Step 2: Calculate. I_lamp = 6 A ÷ 2 = 3 A.
Step 3: Voltage note. Each lamp receives the full battery potential difference.

Final Answer: 3 A through each lamp

Senior Examiner Insight: In parallel circuits, if one bulb blows, the remaining bulbs stay lit because they have independent complete circuits.

Common Pitfalls & Examiner Warnings

Avoid these common mistakes frequently identified by examiners in Key Stage 3 assessments:

Common Mistake: Connecting a voltmeter in series

Voltmeters have huge internal resistance and MUST be connected in parallel around the component.

Common Mistake: Saying voltage 'flows through' a circuit

Current flows THROUGH a circuit; potential difference/voltage is applied ACROSS components.

Common Mistake: Thinking current gets 'used up'

Current is never consumed. The number of electrons entering a component equals the number leaving it.

Interactive Self-Check Quiz (3 Questions)

Test your understanding before checking the full worked answer and examiner mark scheme:

Question 1 of 3

How should an ammeter be connected in a circuit to measure current correctly?

A) In parallel across a bulb

B) In series with the component

C) Outside the circuit

D) Across the battery terminals only

Click to Reveal Answer & Mark Scheme

Correct Answer: B) In series with the component

Detailed Explanation: Ammeters have very low resistance and must be in series so all electric charge flows through them.

Mark Scheme & Scoring Points: 1 mark for connected in series.

Question 2 of 3

A resistor has a resistance of 10 Ω and a current of 2 A passes through it. What is the potential difference?

A) 5 V

B) 20 V

C) 12 V

D) 0.2 V

Click to Reveal Answer & Mark Scheme

Correct Answer: B) 20 V

Detailed Explanation: V = I × R = 2 A × 10 Ω = 20 Volts.

Mark Scheme & Scoring Points: 1 mark for 20 V.

Question 3 of 3

What happens in a series circuit if one bulb breaks?

A) All other bulbs become brighter.

B) The circuit is broken and all bulbs go out.

C) Only the broken bulb turns off; others stay on.

D) The battery catches fire.

Click to Reveal Answer & Mark Scheme

Correct Answer: B) The circuit is broken and all bulbs go out.

Detailed Explanation: A series circuit has only one single continuous path for current. Any break stops the flow entirely.

Mark Scheme & Scoring Points: 1 mark for all bulbs go out due to open/broken circuit.

Created by Fiaraz Iqbal

Former Headteacher & Senior Science / Maths Examiner

With over 15 years of leadership and classroom experience, Fiaraz creates high-yield revision resources aligned with National Curriculum standards to help Key Stage 3 and GCSE students secure top grades.

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