Medium
Physics
Forces, Energy & Light
Motion, energy and light, described without the equations.
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The speed of light in a vacuum is closest to which value?
Electricity and Magnetism
Electricity and magnetism were studied separately for centuries before anyone realised a moving charge produces one and a moving magnet produces the other. This quiz covers both halves.
About this topic
A current in a wire makes a magnetic field, and a magnet moved near a wire makes a current. That reciprocity, worked out in the nineteenth century by Oersted, Faraday and Maxwell among others, is the basis of every motor, generator and transformer in use today. The questions run from circuit basics to the awkward conventions that survive from before anyone knew what was actually moving in a wire. If you have ever wondered why current is said to flow the wrong way, question three has the answer.
Questions & answers
Electricity and Magnetism: all 10 questions and answers
Every question in this quiz is listed below with its correct answer and the reasoning behind it. Play first if you would rather not see the answers — or read through as a study sheet.
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1Ohm's law relates three quantities. Which statement expresses it?
- A Resistance equals voltage multiplied by current
- B Voltage equals current multiplied by resistance Correct
- C Voltage equals current divided by resistance
- D Current equals voltage multiplied by resistance
Answer: B. Voltage equals current multiplied by resistance
Why: Rearranged, it says current rises with voltage and falls as resistance grows. The law holds well for metals at steady temperature but not for components such as diodes and filament lamps.
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2Which unit measures electric current?
- A The ampere Correct
- B The volt
- C The coulomb
- D The watt
Answer: A. The ampere
Why: One ampere is a flow of one coulomb of charge per second. It is one of the seven base units of the SI system, defined since 2019 in terms of the fixed charge on a single electron.
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3Conventional current is drawn flowing from the positive terminal to the negative one. How do electrons actually move in a metal wire?
- A In the same direction as conventional current
- B They vibrate on the spot without any net movement
- C They alternate direction regardless of the supply
- D In the opposite direction, from negative to positive Correct
Answer: D. In the opposite direction, from negative to positive
Why: The convention was fixed before the electron was discovered, and by then it was too entrenched to change. Individual electrons drift remarkably slowly, often less than a millimetre per second, even though the signal itself travels near the speed of light.
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4Moving a bar magnet in and out of a coil of wire produces a voltage across the coil. What is this called?
- A Resistive heating
- B Magnetic saturation
- C Electromagnetic induction Correct
- D Static discharge
Answer: C. Electromagnetic induction
Why: A changing magnetic field through a circuit drives a current, which is Faraday's discovery of 1831 and the principle behind every generator. Nothing happens if the magnet is held still, since the field must be changing.
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5In a simple series circuit, what is true of the current?
- A It is used up gradually as it passes through each component
- B It is the same at every point in the circuit Correct
- C It is largest nearest the battery's positive terminal
- D It divides equally between the components
Answer: B. It is the same at every point in the circuit
Why: Charge is not consumed by components, so the same current passes through every part of a single loop. What does get shared out is the voltage, which divides across the components in proportion to their resistance.
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6What does a fuse in a circuit do?
- A Melts and breaks the circuit if the current gets too high Correct
- B Smooths out fluctuations in the supply voltage
- C Stores charge for use during a power cut
- D Reduces the resistance of the wiring under load
Answer: A. Melts and breaks the circuit if the current gets too high
Why: A thin wire inside heats up and fails once current exceeds the rating, cutting the circuit before the cable can overheat. Circuit breakers do the same job with an electromagnet or a bimetallic strip, and can simply be reset.
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7A bar magnet is cut cleanly in half. What do you have?
- A One piece with only a north pole and one with only a south
- B Two pieces that have lost their magnetism entirely
- C One magnet and one ordinary piece of iron
- D Two smaller magnets, each with a north and a south pole Correct
Answer: D. Two smaller magnets, each with a north and a south pole
Why: Magnetism comes from the alignment of countless tiny regions inside the material, so every fragment keeps both poles. No experiment has ever isolated a single magnetic pole on its own.
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8A compass needle's north-seeking end points towards the Arctic. What does that tell you about the magnetic pole located there?
- A It has no polarity, only field strength
- B It changes polarity with the seasons
- C It is a magnetic south pole Correct
- D It is a magnetic north pole
Answer: C. It is a magnetic south pole
Why: Opposite poles attract, so the pole near geographic north must be magnetically south. That pole also wanders, and has been drifting from Arctic Canada towards Siberia at a brisk pace in recent decades.
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9Mains electricity is distributed as alternating current rather than direct current. What is the main practical reason?
- A Alternating current is harmless to touch
- B Transformers can step the voltage up and down easily, cutting losses over long distances Correct
- C Alternating current travels faster along a cable
- D Direct current cannot pass through copper efficiently
Answer: B. Transformers can step the voltage up and down easily, cutting losses over long distances
Why: High voltage means low current for the same power, and low current means far less energy wasted heating the wires. Transformers only work on a changing field, so they cannot do this job with steady direct current.
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10Rubbing a balloon on your hair makes it stick to a wall. What has happened?
- A Electrons have transferred between the two surfaces, leaving each charged Correct
- B The friction has warmed the balloon so that it softens and grips
- C The rubbing has magnetised the balloon's rubber
- D Air has been forced out from between the balloon and the wall
Answer: A. Electrons have transferred between the two surfaces, leaving each charged
Why: Rubbing moves electrons from one material to the other, and the charged balloon then attracts opposite charge to the surface of the wall. Dry air makes the effect much stronger, which is why static is worse in winter.
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