O-LevelPhysicsElectricity5054/21 · Oct/Nov 2022 · Q67 Marks

An electromagnet is used to separate objects that are magnetic from objects that are non-magnetic. Fig. 6.1 shows the electromagnet suspended from the arm of a crane.

(a)State the name of the metal from which the core of the electromagnet is made.[1]
(b)(i)Calculate the power transferred to the electromagnet.[2]
(b)(ii)The d.c. supply is a set of batteries. The batteries power the magnet for 4.5 hours before they need to be replaced. Calculate the charge driven around the complete circuit in this time.[3]
(c)On a very cold morning, when the electromagnet is first switched on, the current is greater than 39A before decreasing to the usual value. Explain why the current is initially greater than 39A.[1]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2022). The mark or mark type is shown in brackets.

[1] soft iron
[1] (P =) VI or 220 × 39
[1] 8.6 x 10³ W
[1] (Q =) It or 39 × 4.5 or 39 × 4.5 × 60 or 39 × 4.5 × 60 × 60 or 39 x 4.5 x 3600
[1] 180 or 11 000 or 39 × 4.5 × 60 × 60 or 39 x 4.5 x 3600
[1] 6.3 × 10⁵ C
[1] resistance increases with temperature or resistance lower (because of (low / ambient) temperature)

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