GCSE Physics Revision: Electricity and Magnetism Extended theory paper

Electromagnetic effects and CRO

The figure below shows an arrangement that could be used for making an electromagnet or a permanent magnet.

Electromagnetic Effects 1

Two bars of the same size are also available, one made of iron and the other of steel.
(a) (i) State which bar should be used to make a permanent magnet.
     (ii) Describe how the apparatus would be used to make a permanent magnet.
    (iii) Suggest one reason why the circuit contains an ammeter and a variable resistor.
(b) During the making of a permanent magnet, the ammeter reads a steady current of 4.0 A throughout the 5.0 s that the current is switched on. The voltage of the supply is 12V.
Calculate
       (i) the total circuit resistance,
       (ii) the power of the supply,
       (iii) the energy supplied during the 5.0 s.

(c) The potential difference across the variable resistor is 7.0 V and that across the ammeter is zero.
       (i) Calculate the potential difference across the magnetising coil.
     (ii) State the general principle used in making this calculation.