AQA A2 Physics 2016 Paper 4

Hi,

I'm unable to understand this question. Can someone explain this please.

23. A train is travelling at 20 m s–1 along a horizontal track through a uniform magnetic field of flux density 4.0 × 10–5 T acting vertically downwards. What is the emf induced between the ends of an axle 1.5 m long?

A 3.0 × 10−6 V
B 5.3 × 10−4 V
C 1.2 × 10−3 V
D 7.5 × 105 V

Examiner Report - 68% of the students did this correctly. One in
five of them selected distractor B, which could follow from an incorrect formula or substitution (ε = B v/ l).

With no current given how is it possible to derive the solution.

Reply 1

allofthestars

13

Original post by Infinity43965

Hi,

I'm unable to understand this question. Can someone explain this please.

23. A train is travelling at 20 m s–1 along a horizontal track through a uniform magnetic field of flux density 4.0 × 10–5 T acting vertically downwards. What is the emf induced between the ends of an axle 1.5 m long?

A 3.0 × 10−6 V
B 5.3 × 10−4 V
C 1.2 × 10−3 V
D 7.5 × 105 V

Examiner Report - 68% of the students did this correctly. One in
five of them selected distractor B, which could follow from an incorrect formula or substitution (ε = B v/ l).

With no current given how is it possible to derive the solution.

hey

so image the axle as one rod passing through a magnetic field, the change in flux is constant correct? as its constantly travelling throught the field. hence an emf is induced equaly to the Blv = emf. which can be derived from BIL= F and w=fs

hence blv=E , plug all those values in and bingo! thats your answer