A-LevelPhysicsMagnetic fields9702/42 · Oct/Nov 2017 · Q87 Marks

A thin slice of conducting material is placed normal to a uniform magnetic field, as shown in Fig. 8.1. [Figure 8.1] The magnetic field is normal to face CDEF and to face PQRS. The current I in the slice is normal to the faces CDQP and FERS. A potential difference, the Hall voltage VH, is developed across the slice.

(a)(i)State the faces between which the Hall voltage VH is developed. .............................. and ..............................[1]
(a)(ii)Explain why a constant voltage VH is developed between the faces you have named in (i).[4]
(b)Two slices have similar dimensions. One slice is made of a metal and the other slice is made of a semiconductor material. For the same values of magnetic flux density and current, state which slice, if either, will give rise to the larger Hall voltage. Explain your reasoning.[2]

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Mark scheme

Marking points from the official mark scheme (Oct/Nov 2017). The mark or mark type is shown in brackets.

[1] (a)(i) DERQ and CFSP
[1] (a)(ii) charge carriers moving normal to (magnetic) field
[1] (a)(ii) charge carriers experience a force normal to I (and B)
[1] (a)(ii) charge build-up sets up electric field across the slice or build-up of charges results in a p.d. across the slice
[1] (a)(ii) charge stops building up/VH becomes constant when FB = FE
[1] (b) VH inversely proportional to n/number density of charge carriers
[1] (b) number density of charge carriers (n) lower in semiconductors so VH larger for semiconductor slice or VH proportional to v/drift velocity / (for same current) drift velocity (v) higher in semiconductors so VH larger for semiconductor slice

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