CAIE A-Level Physics 20.3.3 Hall Voltage

Practise explaining Hall charge separation and using V_H = BI/(ntq) to calculate Hall voltage, field, current or carrier properties.

Exam points

explain the origin of Hall voltage in a current-carrying material
derive or use V_H = BI/(ntq) to calculate Hall voltage, field, current or carrier quantities
interpret thickness, carrier density and charge sign in the Hall relationship

[Maximum number: 7]

(a)

A rectangular piece of aluminium foil is situated in a uniform magnetic field of flux density B, as shown in Fig. 9.1.

Fig. 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 .

[ 4 ]

(i)

On Fig. 9.1, shade the face of the foil on which electrons initially accumulate.

[ 1 ]

(ii)

Explain why electrons do not continuously accumulate on the face you have shaded.

[ 3 ]

(b)

The Hall voltage $V_{H}$ developed across the foil in (b) is given by the expression

V_{\mathrm{H}}=\frac{B I}{n t q}

where I is the current in the foil.

[ 2 ]

(i)

State the meaning of the quantity n.

[ 1 ]

(ii)

Using the letters on Fig. 9.1, identify the distance t.

[ 1 ]

(c)

Suggest why, in practice, Hall probes are usually made using a semiconductor material rather than a metal.

[ 1 ]

(for semiconductor,) n is (much) smaller so $V_{\mathrm{H}}$ (much) larger

B1

All question bank results loaded