Question

The diagram below shows a wire carrying current toward the top of the page. A positively charged particles is shown moving directly toward the left side of the page at a particular instant.
What is the direction of the force on the positively charged particle at the instant shown, due to the magnetic field produced by the current in the wire?

• A. Toward the top of the page
• B. Toward the bottom of the page
• C. Into the page
• D. Out of the page
• E. Toward the right side of the page

Answer 1

The correct option is B Toward the bottom of the page

Magnetic field at point P due to straight wire $\overrightarrow{B}=-B$ $\hat{z}$

From figure, $\overrightarrow{v}=-v$ $\hat{x}$

Magnetic force on the charge $\overrightarrow{F}=q(\overrightarrow{v}\times \overrightarrow{B})=q\left[\right(-v)\hat{x}\times (-B\left)\hat{z}\right]=-qvB$ $\hat{y}$

Thus magnetic force on the charge particle acts towards the bottom of the page.