(a) zero
(b) increasing
(c) decreasing
(d) constant
Answer: (d) Constant
Explanation:
CONCEPT
- When
a conductor or coil moves in a magnetic field, an EMF
is induced due to Faraday’s law.
- If
the coil is short-circuited, the induced EMF produces a current.
- According
to Lenz’s law, the induced current opposes the cause producing
it.
- Hence,
a magnetic (Lorentz) force acts on the coil, opposing its
motion.
Physics of the Falling Coil
- As
the coil falls vertically, it cuts horizontal magnetic flux lines.
- This
induces a current in the short-circuited coil.
- The
induced current produces a magnetic field that:
- Opposes
the downward motion of the coil
- Creates
an upward magnetic force
Constant Rate of Flux Cutting
- The
magnetic field is uniform.
- The
coil cuts magnetic flux at a constant rate while it
remains fully inside the field.
- Therefore:
- Induced
EMF is constant
- Induced
current is constant
- Upward
magnetic force is constant
Net Force on the Coil
- Two
forces act on the coil:
- Downward
force = Weight (mg)
- Upward
force = Magnetic force (constant)
- Net
force:
- Since
both forces are constant, the net force is constant.
Acceleration of the Coil
- From
Newton’s second law:
- Since
is constant:
- Acceleration
is constant
- Because
the magnetic force opposes gravity:
- Acceleration
is less than
FINAL CONCLUSION
- A
short-circuited coil falling through a uniform magnetic field experiences:
- A
constant upward magnetic force
- A
constant net downward force
- Hence,
a constant acceleration less than
Correct Answer
✅ Option (d)
Constant acceleration (less than )
✔️ Key One-Line Exam Statement
A short-circuited coil falling in a uniform magnetic
field moves with constant acceleration less than gravity due to a constant
opposing magnetic force.