Question 22: NCERT Solutions for 12th Class Physics: Chapter 5-Magnetism and Matter
A monoenergetic (18 keV) electron beam initially in the horizontal direction is subjected to a horizontal magnetic field of 0.4 G normal to the initial direction. Estimate the up or dowri deflection of the beam over a distance of 30 cm (me = 9.11 × 10-31 kg). [Note: Data in this exercise are so chosen that the answer will give you an idea of the effect of earth’s magnetic field on the motion of the electron beam from the electron gun to the screen in a TV set.]
Solution:
Kinetic energy of electron
Velocity in x direction remains constant, hence time to cross 30 cm
A magnetic force F = euB is acting in vertical direction, which provides acceleration in vertical direction
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NCERT Solutions for 12th Class Physics: Chapter 5-Magnetism and Matter