Moving Charges and Magnetism

A proton is moving undeflected in a region of crossed electric and magnetic fields at a constant speed of 2 105 m s-1. When the electric field is switched off, the proton moves along a circular path of radius 2 cm . The magnitude of electric field is x 104 N/C. The value of x is . Take the mass of the proton =1.6 10-27 kg.

Answer

2

Solution

[figure]

Undeflected: qE=qvB E=vB; E off: qvB= mv2r B= mvqr

E= mv2qr= (1.6 10-27)(2 105)2(1.6 10-19)(2 10-2)=2 104 N/C

x=2

Answer: 2