State what is meant by a magnetic field.

1. (a)State what is meant by a magnetic field.[2]
2. (b)A rectangular piece of aluminium foil is situated in a uniform magnetic field of flux density B, as shown in [Figure 9.1]. The magnetic field is normal to the face PQRS of the foil. Electrons, each of charge –q, enter the foil at right angles to the face PQTV.
3. (b)(i)On [Figure 9.1], shade the face of the foil on which electrons initially accumulate.[1]
4. (b)(ii)Explain why electrons do not continuously accumulate on the face you have shaded.[3]
5. (c)The Hall voltage VH developed across the foil in (b) is given by the expression VH = BI / ntq where I is the current in the foil.
6. (c)(i)State the meaning of the quantity n.[1]
7. (c)(ii)Using the letters on [Figure 9.1], identify the distance t.[1]
8. (d)Suggest why, in practice, Hall probes are usually made using a semiconductor material rather than a metal.[1]

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