Rankers Physics

Force Acting on Moving Charges: Practice Problem & Solution

A uniform magnetic field acts right angles to the direction of motion of electrons. As a result, the electron moves in a circular path of radius $2\text{ cm}$. If the speed of electrons is doubled, then, the radius of the circular path will be (1991)
$2.0 \text{ cm}$
$0.5 \text{ cm}$
$4.0 \text{ cm}$
$1.0 \text{ cm}$

Solution Explained:

To solve this problem, we apply the core principles of Force Acting on Moving Charges. Understanding the underlying formula is key to arriving at the correct answer below:

The radius of the circular path is given by $$r = \frac{mv}{qB}$$. Since $r \propto v$, doubling the speed doubles the radius to $4.0\text{ cm}$.

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