Practise analysing magnetic force direction and magnitude, Hall measurements, charged-particle paths and velocity selection in electric and magnetic fields.
A uniform magnetic field is now applied in the region of the electric field in Fig. 5.1, so that the electron in (b)(iii) travels undeviated through the region.
Determine the direction of the uniform magnetic field.
Explain, with reference to the forces exerted by the two fields on the electron, why the path of the electron is undeviated.
Determine the flux density B of the uniform magnetic field. Give a unit with your answer.
B= unit
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 .
On Fig. 9.1, shade the face of the foil on which electrons initially accumulate.
Explain why electrons do not continuously accumulate on the face you have shaded.
The Hall voltage developed across the foil in (b) is given by the expression
where I is the current in the foil.
State the meaning of the quantity n.
Using the letters on Fig. 9.1, identify the distance t.
Suggest why, in practice, Hall probes are usually made using a semiconductor material rather than a metal.