Q12

The diagram shows a discharge tube used by Thomson to investigate cathode rays. When the connections are made to a high-voltage power supply, cathode rays are produced at C and accelerated across AB and through parallel plates P and Q, connected to a second power supply, with P positively charged. The rays then hit the centre of the fluorescent screen when a magnetic field is positioned in the XY direction between plates P and Q.

Which row of the table shows the aim of this experiment and the correct direction of the applied magnetic field?

	Aim of the experiment	Direction of magnetic field
A.	To determine the charge of the electron	From X to Y
B.	To determine the charge of the electron	From Y to X
C.	To determine the charge to mass ratio of the electron	From X to Y
D.	To determine the charge to mass ratio of the electron	From Y to X