Solveeit Logo
Login

Question

Physics Question on Moving charges and magnetism

A beam of electrons is moving with constant velocity in a region having electric and magnetic fields of strength 20Vm−120 V m^{-1} and 0.5 T at right angles to the direction of motion of the electrons. What is the velocity of the electrons?

A

8 ms−1 8\, ms^{-1}

B

5.5 ms−1 5.5 \,ms^{-1}

C

20 ms−1 20\, ms^{-1}

D

40 ms−1 40 \,ms^{-1}

Answer

40 ms−1 40 \,ms^{-1}

Explanation

Solution

Electric field (E) = 20 V/m and magnetic field
(B) = 0.5 T.
The force on electron in a magnetic field = evB
Force on electron on an electric field = eE
Since the electron is moving with constant
velocity, therefore the resultant force on electron
is zero.
i.e eE=evB⇒v=E/B=20/0.5=40 ms−1 eE = ev B \Rightarrow v= E/B = 20/0.5 = 40 \,ms^{-1}