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# There exists uniform electric and magnetic fields in space. A particle is moving with a velocity $\overrightarrow v$ and suddenly a hollow metallic cube is enclosed around it. The change in force exerted on the particle is

$\begin {array} {1 1} (a)\;q\overrightarrow v \times \overrightarrow B & \quad (b)\;q \overrightarrow E \\ (c)\;q ( \overrightarrow E+ \overrightarrow v \times \overrightarrow B) & \quad (d)\;Zero \end {array}$

Electric force on the particle vanishes due to electrostatic shielding.
There is no corresponding analogue of magnetic shielding and hence the magnetic field continues to act as it is.
Ans : (b)