Question

Calculate the speed of an electron if it travels in a circular path of radius 50 cm in a magnetic field of 5 × 10^-3 T.

(a) 440 × 10^7 m/s

(b) 4 × 10^7 m/s

(c) 44 × 10^7 m/s

(d) 0.4 × 10^7 m/s

I got this question in homework.

This interesting question is from Motion in Combined Electric and Magnetic Field in section Moving Charges and Magnetism of Physics – Class 12

Answer 1

Right option is (c) 44 × 10^7 m/s

The best I can explain: Magnetic force on the electron = Centripetal force on the electron.

evB = \(\frac {mv^2}{r}\),

v = \(\frac {eBr}{m}\)

v = \(\frac {(1.6 \, \times \, 10^{-19} \, \times \, 5 \, \times \, 10^{-3} \, \times \, 50 \, \times \, 10^{-2})}{(9.1 \, \times \, 10^{-31})}\)

v = 43.95 × 10^7 m/s ≈ 44 x 10^7 m/s.