Question

A conducting rod $PQ$ of length $L=1.0\text{m}$ is moving with a uniform speed $V=2.0\text{m/s}$ in a uniform magnetic field $B=4.0T$ directed into the paper. A capacitor of capacity $C=10\mu F$ is connected as shown in figure. Then

• A. $q_A=+80\mu C$ and $q_B=-80\mu C$
• B. $q_A=-80\mu C$ and $q_B=+80\mu C$
• C. $q_A=0=q_B$
• D. Charge stored in the capacitor increases exponentially with time

Answer 1

The correct option is A $q_A=+80\mu C$ and $q_B=-80\mu C$

$q=C\epsilon =C\left(BVl\right)$
$=(10\times {10}^{-6})\left(4\right)\left(2\right)\left(1\right)$
$=80\mu C=\text{constant}$
Magnetic force on electron on the coducting rod $PQ$ is towards $Q$. Therefore $A$ is positively charged and $B$ is negatively charged.