6 exam-style questions with full mark schemes and model answers. Write your own answer and the AI examiner marks it against the mark scheme.
Learn this properly: Magnets and Magnetic FieldsA simple direct-current (d.c.) electric motor consists of a rectangular coil of wire placed between the poles of a permanent magnet. When a current flows through the coil, the coil spins.
Describe and explain how the motor works. In your answer refer to the motor effect, the forces on the two sides of the coil, and explain the job of the split-ring commutator in keeping the coil turning the same way. (6 marks)
A straight wire carrying a current sits at right angles to a magnetic field, and experiences a force (the motor effect). (This question is Higher-tier content.)
The length of wire in the field is 0.15 m, the current is 4.0 A, and the magnetic flux density is 0.20 T.
(a) Calculate the force on the wire. Use F=BIL. Show your working and give the unit. (2 marks)
(b) The current is now increased to 10 A, while the flux density and length stay the same. Calculate the new force on the wire. (2 marks)
A step-down transformer is used to convert the mains supply for a doorbell. The primary coil has 2400 turns and is connected to a 240 V supply. (This question is Higher-tier content.)
Calculate the number of turns needed on the secondary coil to give an output potential difference of 12 V. Use VsVp=NsNp. Show your working. (3 marks)
An ideal transformer wastes no energy, so the power delivered to the secondary coil equals the power supplied to the primary coil. (This question is Higher-tier content.)
A transformer has a primary p.d. of 230 V and draws a primary current of 0.50 A. The output (secondary) potential difference is 46 V.
Calculate the current in the secondary coil. Use VpIp=VsIs. Show your working and give the unit. (3 marks)
A bar magnet is pushed into a coil of wire that is connected to a sensitive voltmeter. As the magnet moves, the voltmeter shows a reading — this is the generator effect.
Explain why a potential difference is induced only while the magnet is moving, and state two changes that would produce a larger induced potential difference. (2 marks)
Magnets can be classified as permanent magnets or induced magnets.
State the difference between a permanent magnet and an induced magnet. (1 mark)