Question

Electrons in a TV tube move horizontally South to North. Vertical component of earth's magnetic field points down. The electron is deflected towards which direction? [$F=q(\overrightarrow{v}\times \overrightarrow{B}$)]

• A. West
• B. No deflection
• C. East
• D. North to South

Answer 1

The correct option is C East

We know that a charge placed in a magnetic field experiences a force given by: $F=q(\overrightarrow{v}\times \overrightarrow{B})$
But here the electrons move horizontally South to North and the vertical component of earth's magnetic field points down. Hence,
$F=q(\overrightarrow{v}\times \overrightarrow{B})=-e(\hat{j}\times \widehat{-k})=\hat{i}e$.
Thus, the electron is deflected towards east.