Question

A monoenergetic (18 keV) electron beam initially in the horizontal direction is subjected to a horizontal magnetic field of 0.04 G normal to the initial direction. Estimate the up or down deflection of the beam over a distance of 30 cm (m_e = 9.11 x 10^-31 kg).

Answer 1

M = 9.11 x 10^-31 kg

C = 1.6 x 10^-19 C

B = 0.40 G = 0.4 x 10^-4 T

\(\frac{1}{2}\)mV² = 18KeV = 18 x 1.6 x 10^-16 J

suppose that the electron moves along a circular path of radius r under the effect of magnetic field. Then

Figure shows an electron covering a circular path PQ, C = 30 cm = 0.3 m and of radius OP = OQ = 11.32m

It follows the electron will undergo a deflection PA in downward direction, while it covers a distance PQ. IF θ is angle subtended by PQ