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Electricity and circuits

Use current, potential difference and resistance relationships in simple series and parallel circuits.

12 free questions · Notes · Worked solutions

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What you will practise

  • Define current, potential difference and resistance.
  • Apply Ohm's law to an ideal resistor.
  • Describe current and voltage in series and parallel circuits.
  • Calculate electrical power and energy in simple circuits.

Revision notes

Current and charge

Current is the rate of flow of charge: I=Q/t. It is measured in amperes. Conventional current is defined from positive to negative around a circuit.

Potential difference and resistance

Potential difference is energy transferred per unit charge. For an ohmic resistor at constant temperature, V=IR. Resistance is measured in ohms; this model assumes the resistor's physical conditions remain stable.

Series and parallel

In series, current is the same through each component and supply voltage is shared. In parallel, each branch has the same potential difference; branch currents add to the total.

Power and safety

Electrical power P=IV and energy E=Pt. A fuse melts when excessive current heats it. Use circuit symbols and connect an ammeter in series and a voltmeter in parallel.

A worked example

An ideal 6 Ω resistor is connected to a 12 V supply. Find the current and power dissipated.

  1. Use Ohm's law to find the current.
  2. I=V/R=12/6=2 A.
  3. P=VI=12×2=24 W.

2 A; 24 W

Try it yourself

These are original practice questions, not official past-paper questions. Practice points count correct final answers; working is not automatically assessed.

Choose a question to begin.
Question 1 · Standard1 practice point

A 4 Ω resistor is connected across 12 V. Find the current.

Need a hint?

Use I=V/R.

Worked solution
  1. I=12/4=3 A.
Question 2 · Standard1 practice point

A current of 2 A flows for 5 s. How much charge passes a point?

Need a hint?

Use Q=It.

Worked solution
  1. Q=2×5=10 C.
Question 3 · Standard1 practice point

Two 3 Ω resistors are connected in series. What is their combined resistance?

Need a hint?

Resistances add in series.

Worked solution
  1. Rtotal=3+3=6 Ω.
Question 4 · Standard1 practice point

A 2 A current flows through a component with 5 V across it. Find its power.

Need a hint?

Use P=IV.

Worked solution
  1. P=2×5=10 W.
Question 5 · Foundation2 practice points

An ideal 10 Ω resistor is connected across a 20 V supply. Find the current.

Need a hint?

Use I=V/R.

Worked solution
  1. I=20/10.
  2. I=2 A.
Question 6 · Standard2 practice points

A current of 0.5 A flows for 40 s. Find the charge transferred.

Need a hint?

Q=It.

Worked solution
  1. Q=0.5×40.
  2. Q=20 C.
Question 7 · Standard2 practice points

A 6 V supply produces a current of 0.3 A through an ideal resistor. Find the resistance.

Need a hint?

Rearrange V=IR.

Worked solution
  1. R=V/I=6/0.3.
  2. R=20 Ω.
Question 8 · Standard2 practice points

A 12 V lamp draws 0.5 A. Find its power.

Need a hint?

Use P=IV.

Worked solution
  1. P=12×0.5.
  2. P=6 W.
Question 9 · Stretch3 practice points

Two ideal resistors, 4 Ω and 6 Ω, are connected in series to a 20 V supply. Find the circuit current.

Need a hint?

Add series resistance, then apply Ohm's law.

Worked solution
  1. Rtotal=4+6=10 Ω.
  2. I=V/R=20/10.
  3. I=2 A.
Question 10 · Stretch3 practice points

A 3 Ω resistor and a 6 Ω resistor are connected in parallel across an ideal 12 V supply. Find the total current.

Need a hint?

Find each branch current using the same 12 V, then add them.

Worked solution
  1. Current in 3 Ω branch=12/3=4 A.
  2. Current in 6 Ω branch=12/6=2 A.
  3. Total current=4+2=6 A.
Question 11 · Standard2 practice points

A 60 W device operates for 5 minutes. Find the energy transferred in joules.

Need a hint?

Convert minutes to seconds, then use E=Pt.

Worked solution
  1. 5 min=300 s.
  2. E=60×300=18 000 J.
Question 12 · Standard2 practice points

A potential difference of 9 V transfers 36 J of energy. How much charge moves?

Need a hint?

Potential difference V=E/Q.

Worked solution
  1. Q=E/V=36/9.
  2. Q=4 C.

Coverage and sources

Selected IGCSE concepts, with a mix of introductory and more demanding questions. Check your own specification. AI drafted; independent teacher review is pending. Editorial details.

Cambridge IGCSE Physics 0625 syllabus

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