A-LevelPhysicsAlternating currents9702/41 · Oct/Nov 2020 · Q99 Marks
Define magnetic flux.
- (a)Define magnetic flux.[2]
- (b)(i)A simple transformer consists of two coils of wire wound on a soft-iron core, as illustrated in Fig. 9.1. [Figure 9.1]. There is a sinusoidal current in the primary coil. Explain: how this current gives rise to an induced electromotive force (e.m.f.) in the secondary coil[3]
- (b)(ii)why the e.m.f. induced in the secondary coil is not constant.[2]
- (c)Explain why the soft-iron core in (b) is laminated.[2]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2020). The mark or mark type is shown in brackets.
- [M1] flux density × area
- [A1] where flux is normal to area
- [M1] flux density × area × sin θ
- [A1] where θ is angle between flux direction and (plane of) area
- [B1] (alternating) current creates changing (magnetic) flux
- [B1] core links (magnetic) flux with secondary coil
- [B1] changing flux (in secondary) causes induced e.m.f.
- [B1] rate of change of flux is not constant
- [B1] (induced) e.m.f. is proportional to rate of change of flux
- [B1] reduces induced currents in core
- [B1] hence reduces energy losses (in core)
Write your answer and get it marked
On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.
Sign up free →