In the figure shown, the conductor $PQ$ of length $l$ is moved from $x = 0$ to $x = b$ and then up to $x = 2b$ with a constant velocity $\vec{v}$. $A$ uniform magnetic field $\vec{B}$ is perpendicular to the plane of the paper and extends from $x = 0$ to $x = b$, and it is zero for $x > b$. The magnitude of the emf induced in the conductor is:

• A
  $Blv$ for $0 \le x < b$ and $0$ for $b \le x < 2b$
• B
  $0$ for $0 \le x < b$ and $Blv$ for $b \le x < 2b$
• C
  $Blv$ for all $x$ from $0$ to $2b$
• D
  $0$ for all $x$ from $0$ to $2b$