Q134 / 180 · COMEDK 2015 · Physics
A bicycle generator crcates $1.5 \mathrm{~V}$ at $15 \mathrm{~km} / \mathrm{h}$. The cmf generated at $10 \mathrm{~km} / \mathrm{h}$ is
- A$1.5 \mathrm{~V}$
- B$2 \mathrm{~V}$
- C$0.5 \mathrm{~V}$
- Correct answerD$1 \mathrm{~V}$
Solution
Initial speed of bicycle, $v_{1}=15 \mathrm{~km} / \mathrm{h}$
Emf produced, $e_{1}=15 \mathrm{~V}$
Final speed of bicycle, $v_{2}=10 \mathrm{~km} / \mathrm{h}$
If emf generated at speed $v_{2}$ be $e_{2}$, then
$$
\begin{array}{ll}
& e=B v l \\
\Rightarrow & e \propto v \\
\Rightarrow & \frac{e_{2}}{e_{1}}=\frac{v_{2}}{v_{1}}=\frac{10}{15} \\
\Rightarrow & \frac{e_{2}}{e_{1}}=\frac{2}{3} \Rightarrow e_{2}=\frac{2}{3} e_{1}=\frac{2}{3} \times 15=1 \mathrm{~V}
\end{array}
$$
Hence, the correct answer is option: 'D'.