Q120 / 160 · JIPMER 2010 · Physics
The magnetic flux linked with a coil at any instant $t$ is given by the equation $\phi=5 t^3-100 t+300$. The magnitude of emf induced in the coil after 3 s is
- A10V
- B20V
- Correct answerC35V
- D70V
Solution
Given,
$\begin{aligned}
\phi & =5 t^3-100 t+300 \\
e & =-\frac{d \phi}{d t}=\frac{-d}{d t}\left(5 t^3-100 t+300\right)
\end{aligned}$
$\begin{gathered}
=-\left(15 t^2-100+0\right) \\
=-15 t^2+100 \\
\therefore \quad \frac{e}{t}=-15(3)^2+100=-15 \times 9+100 \\
=-135+100=-35 \mathrm{~V}
\end{gathered}$
Minus sign signifies the Lenz's law
Hence, the correct answer is option: 'C'.