Question

The acceleration of an electron at a certain moment in a magnetic field $\overset{ \rightarrow }{B}=\left(2 \hat{i} + 3 \hat{j} + 4 \hat{k}\right)T$ is $\overset{ \rightarrow }{a}=\left(x \hat{i} + \hat{j} - \hat{k}\right)ms^{- 2}$ . The value of $x$ is :

• A. $0.5$
• B. $1$
• C. $2.5$
• D. $1.5$

Answer 1

Answer: (A)

$\overset{ \rightarrow }{B}\cdot \overset{ \rightarrow }{F}=0$
As $\overset{ \rightarrow }{B}\bot\overset{ \rightarrow }{F}$
$\therefore \overset{ \rightarrow }{B}\cdot \overset{ \rightarrow }{a}=0$
or $2x+3-4=0$
$\therefore x=0.5$