Course: Combined and Separate (questions marked Separate are Physics only) | Find each scene on YouTube, watch it, then answer the questions. Write your answers on paper first, then tap Show answer.
Equations: F = BIl (HT) · Vp ÷ Vs = np ÷ ns (Separate) · Vp × Ip = Vs × Is (Separate)
Magnetic materials: iron, steel, nickel and cobalt.
1. Toy Story 3 – lifted by the giant magnet
🎬 The scene: At the dump, a giant overhead magnet lifts metal objects off the conveyor belt – and the toys grab on to escape.
Q1 (F) The toys grab metal objects to be lifted. Why isn’t a plastic toy pulled up on its own?
Show answer
Plastic is not a magnetic material. Only iron, steel, nickel and cobalt are attracted to magnets.
Q2 (F/H) Rubbish dumps use electromagnets, not permanent magnets. Give one advantage, and two ways to make an electromagnet stronger.
Show answer
It can be switched off to drop the load. Stronger: increase the current, add more turns on the coil, or use an iron core.
Q3 (H) A steel can is not a magnet, yet it is attracted to the electromagnet. Explain why.
Show answer
The can becomes an induced magnet when placed in the magnetic field. Induced magnetism always causes attraction, and the can loses its magnetism when removed from the field.
2. Finding Nemo – turtles navigating the ocean
🎬 The scene: Crush and the sea turtles ride the East Australian Current. Real sea turtles can sense the Earth’s magnetic field to find their way across oceans.
Q1 (F) What does a compass needle do, and why?
Show answer
It points north. The needle is a small magnet that lines up with the Earth’s magnetic field.
Q2 (F/H) What evidence does a compass give that the Earth has a magnetic core?
Show answer
Away from other magnets, a compass always points the same way (north), showing the Earth itself produces a magnetic field, like a giant bar magnet.
Q3 (H) The north pole of a compass needle points to the Earth’s geographic North Pole. What type of magnetic pole must be there? Explain.
Show answer
A magnetic south pole. Unlike poles attract, so the needle’s north pole is pulled towards a south pole.
3. Toy Story – RC car to the rescue
🎬 The scene: Woody and Buzz race after the moving van on RC – until RC’s batteries run out.
Q1 (F) RC is driven by an electric motor. What is the motor effect?
Show answer
When a wire carrying a current is placed in a magnetic field, it experiences a force.
Q2 (F/H) RC slows down and stops when his batteries run out. Explain why, and give two ways to make a motor spin faster.
Show answer
No current means no force on the coil, so the motor stops. Faster: increase the current, use a stronger magnet, or add more turns to the coil.
Q3 (H) A 0.05 m length of wire in the motor carries 2 A in a 0.2 T field. Calculate the force on it.
Show answer
F = BIl = 0.2 × 2 × 0.05 = 0.02 N
4. Back to the Future – the giant loudspeaker
🎬 The scene: At the start of the film, Marty turns Doc’s giant amplifier up full, strums one chord – and is blown across the room by the speaker.
Q1 (F, Separate) A loudspeaker contains a coil and a permanent magnet. What effect makes the cone move?
Show answer
The motor effect – the current in the coil, in the magnet’s field, produces a force.
Q2 (F/H, Separate) The speaker is supplied with alternating current. Explain how this makes a sound wave.
Show answer
The current keeps changing direction, so the force on the coil keeps changing direction. The coil and cone vibrate back and forth, pushing the air to make pressure waves – sound.
Q3 (H, Separate) Real or fake? What happens to the sound when Marty turns the volume up? Could a speaker really blow him across the room?
Show answer
A bigger current gives a bigger force, so the cone vibrates with a larger amplitude – a louder sound. But sound waves transfer energy, not a steady push of air, so they couldn’t throw a person across a room. Fake!
5. Big Hero 6 – GoGo’s electromagnetic bike
🎬 The scene: Hiro meets GoGo Tomago in the university lab, testing her super-fast bike that uses electromagnetic suspension.
Q1 (F) GoGo’s wheel floats on electromagnetic suspension. What happens when two like poles face each other?
Show answer
They repel – this repulsion can hold an object up without touching.
Q2 (F/H) Maglev trains float above the track. Why can they travel faster than normal trains?
Show answer
There is no friction between the wheels and the rails, so much less energy is wasted and there’s less wear.
Q3 (H) Why are electromagnets, rather than permanent magnets, used to control the height of a maglev train?
Show answer
The strength of an electromagnet can be changed by changing the current, so the force can be adjusted constantly to keep the train at the right height – and it can be switched off.
6. The Boy Who Harnessed the Wind – building a generator
🎬 The trailer: William Kamkwamba builds a wind turbine from scrap, using a bicycle dynamo as the generator.
Q1 (F, Separate) William’s bicycle dynamo is a generator. How does moving a magnet near a coil produce electricity?
Show answer
When the magnet moves relative to the coil, the coil cuts magnetic field lines and a potential difference is induced (the generator effect). If the coil is part of a complete circuit, a current flows.
Q2 (F/H, Separate) Give three ways to increase the induced potential difference.
Show answer
Spin it faster, use a stronger magnet, or use more turns on the coil.
Q3 (H, Separate) What is the difference between the output of an alternator and a dynamo?
Show answer
An alternator produces alternating current (it uses slip rings). A dynamo produces direct current (it uses a split-ring commutator).
7. Cloudy with a Chance of Meatballs – the sub-station
🎬 The scene: Flint runs a cable from the town’s power sub-station to his food machine.
Q1 (F, Separate) A sub-station contains step-down transformers. What do they do?
Show answer
They decrease the potential difference of the supply so it is safe to use in homes.
Q2 (F/H, Separate) A transformer steps 11 000 V down to 230 V. The primary coil has 4400 turns. How many turns are on the secondary coil?
Show answer
Vp ÷ Vs = np ÷ ns, so 11 000 ÷ 230 = 4400 ÷ ns. ns = 4400 × 230 ÷ 11 000 = 92 turns
Q3 (H, Separate) The primary current is 2 A. Assuming 100% efficiency, calculate the secondary current.
Show answer
Vp × Ip = Vs × Is: 11 000 × 2 = 230 × Is, so Is = 22 000 ÷ 230 = 96 A (to 2 s.f.)
8. The Iron Giant – the power station
🎬 The scene: Hogarth finds the Giant eating the cables at a power sub-station and saves him from being electrocuted.
Q1 (F) A current flows through each cable at the power station. What is produced around each cable?
Show answer
A magnetic field.
Q2 (F/H) Describe the shape of the magnetic field around a straight wire, and two ways to make it stronger.
Show answer
Concentric circles around the wire. It is stronger with a bigger current and closer to the wire.
Q3 (H, Separate) Explain why transformers only work with alternating current.
Show answer
AC in the primary coil makes a changing magnetic field in the iron core. This changing field passes through the secondary coil and induces a potential difference. DC makes a steady field, which induces nothing.
9. Spider-Man 2 – the reactor pulls in metal
🎬 The scene: Dr Octavius’s fusion experiment goes out of control and its powerful magnetic field starts pulling metal objects towards the reactor. (12A: action.)
Q1 (F) As the experiment goes wrong, metal objects fly towards the reactor. Which of these would really be attracted by a magnet: a steel spanner, a copper coin, an aluminium can, an iron nail?
Show answer
The steel spanner and the iron nail. Copper and aluminium are metals but are not magnetic.
Q2 (F/H) Objects closer to the reactor are pulled harder. What does this tell you about magnetic fields?
Show answer
The magnetic field is strongest close to the magnet and gets weaker with distance (field lines are closer together near the source).
Q3 (H) Real or fake? Glass shatters and is pulled in too. Is that realistic for a magnetic field? Explain.
Show answer
Fake. Glass is not a magnetic material, so a magnetic field would not pull it. Only magnetic materials like iron and steel would be attracted.
10. Big Hero 6 – Baymax needs charging
🎬 The scene: Baymax’s battery runs low and Hiro has to get him home to his charging station.
Q1 (F, Separate) Battery chargers plug into the 230 V mains. Why do they contain a transformer?
Show answer
To step down the 230 V mains to a much lower potential difference suitable for the battery.
Q2 (F/H, Separate) The transformer has 2300 turns on the primary coil and 100 on the secondary. Calculate the output potential difference.
Show answer
Vs = Vp × ns ÷ np = 230 × 100 ÷ 2300 = 10 V
Q3 (H, Separate) Batteries need direct current to charge. Why can’t the charger just use a transformer on its own?
Show answer
A transformer’s output is still alternating current. The charger also needs a circuit (using diodes) to convert the AC into DC before it can charge the battery.
Teachers: the buttons open a YouTube search, so you can pick whichever upload is currently available. Please watch the clip through before showing it to a class.
