Question

If a coil of $50$ turns area $5.0c{m}^2$ is suddenly removed from magnetic field. It is observed that charge of $5\times {10}^{-4}C$ flows into the coil. If the resistance of the coil is $100\Omega$, the magnetic flux density in $Wb/m^2$ is

• A. $2$
• B. $3$
• C. Zero
• D. $5$

Answer 1

The correct option is A $2$

Amount of charge flowing is

$\Delta Q=\frac{\Delta \varphi }{R}$
$\Rightarrow \Delta \varphi =\Delta Q\times R$
$\Rightarrow \Delta \varphi =5\times {10}^{-4}\times 100$

By definition $\Delta \varphi ={\varphi }_f-{\varphi }_i$
$NBA-0=5\times {10}^{-2}$
$50\times B\times 5\times {10}^{-4}=5\times {10}^{-2}$
$B=2T$