Torque

To solve the problem, we need to analyze the variation of the induced emf in a conducting triangular loop moving through a region of uniform magnetic field.

1. Understanding the Setup:
- The loop PQR is an equilateral triangle of height moving along the -direction.
- The magnetic field is uniform and points in the -direction.
- At , vertex P enters the magnetic field region.
- The induced emf is related to the rate of change of magnetic flux through the loop.

2. Variation of Flux and emf:
- Initially, no part of the loop is inside the magnetic field, so .
- As the loop enters the field (from to ), the area inside the field increases linearly, so flux increases linearly.
- The emf is proportional to the rate of change of flux.
- When half the loop enters ( ), the rate of change of area changes slope.
- Between and , the loop is leaving the field and the flux decreases.
- Beyond , the loop is completely outside, so .

3. Shape of emf vs. distance graph:
- The emf starts at zero at , decreases (negative slope) until , then increases until .
- After , emf is zero until , then increases positively until , and finally returns to zero.
- This corresponds to graph (A) with negative and positive triangular peaks.

Final Answer:
Option (A)