Two straight conducting rails form a right angle as shown below. A conducting bar in contact with the rails starts at the vertex at time $t=0$ and moves with constant velocity of $v=5 \mathrm{m} {\mathrm{s}}^{-1}$ along them. A magnetic field with $B=0.1 T$ is directed out of the page. The absolute value of the $\mathrm{emf}$ around the triangle at the time $t=4 \mathrm{s}$ will be?

• A

  $10 \mathrm{V}$
• B

  $15 \mathrm{V}$
• Correct answer
  C

  $20 \mathrm{V}$
• D

  $30 \mathrm{V}$

Hence, the correct answer is option: 'C'.