Moving Charges and Magnetism - Result Question 27
27. A uniform magnetic field acts at right angles to the direction of motion of electron. As a result, the electron moves in a circular path of radius $2 cm$. If the speed of electron is doubled, then the radius of the circular path will be
[1991]
(a) $2.0 cm$
(b) $0.5 cm$
(c) $4.0 cm$
(d) $1.0 cm$
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Answer:
Correct Answer: 27. (c)
Solution:
(c) $r=\frac{m v}{q B}$ or $r \propto v$
As $v$ is doubled, the radius also becomes double.
Hence, radius $=2 \times 2=4 cm$
