Question

36. A beam of electrons is moving with constant
velocity in a region having electric and magnetic
fields of strength 20 Vm-1 and 0.5 T at right angles
to the direction of motion of the electrons. What is
the velocity of the electrons?
(1) 8 ms-1
(2) 5.5 ms-1
(3) 20 ms-1
(4) 40 ms-1

Answer 1

Answer:

(4)

Electric and magnetic fields would be equal

See page 182 , point no. 2

Answer 2

The velocity of the electrons is 40 m/s.

Explanation:

Given that,

Electric field strength, E = 20 V/m

Magnetic field strength, B = 0.5 T

Here, the electron is moving with constant velocity, therefore the resultant force on electron is zero. So,

$qE=qvB\\\\v=\dfrac{E}{B}\\\\v=\dfrac{20}{0.5}\\\\v=40\ m/s$

So, the velocity of the electrons is 40 m/s.

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Electric and magnetic field