ELECTRIC MOTORS AND ELECTROMAGNETIC INDUCTION
3 marks · NormalA coil is used to make an electromagnet by wrapping it around a nail and connecting it to a battery.
Describe how the magnetic field produced by the coil is different from the field produced by a straight wire.
State two ways in which the strength of this electromagnet can be increased.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) The field around a coil is similar to a bar magnet (has a north and south pole), while a straight wire has concentric circles (no poles).
(b) Increase number of turns, increase the current, use a soft iron core. · must show Any two correct ways
Must show: Correct field difference, Two distinct ways to increase strength
Also accept: Field around coil is like a bar magnet; field around wire is circular
Common mistakes: Naming factors not affecting strength (e.g., shape of core instead of its material)
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Explains difference: coil field has poles/bar magnet pattern; straight wire has circles.
B1 (b) · 2 marks · States two ways to increase electromagnet strength (any from: more turns, higher current, soft iron core).
Worked solution
a) The magnetic field around a coil is like a bar magnet, with a clear north and south pole. Around a straight wire, the field forms concentric circles around the wire.
b) Increase the current, add more turns/coils, or use a soft iron core to increase the magnet's strength.