Question

Eddy currents are produced when

• A. a thick metal plate is kept in a steady magnetic field
• B. a circular coil is placed in a steady magnetic field
• C. a steady current is passed through a coil
• D. a thick metal plate is kept in a varying magnetic field

Hint:

The word "currents" implies induction, and induction always requires a change over time. Look for dynamic keywords like "varying" or "moving" and eliminate static keywords like "steady" or "constant."

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
We need to identify the exact physical conditions required to generate eddy currents inside a conductive material.

Step 2: Key Formula or Approach:
Eddy currents are driven by Faraday's Law of Electromagnetic Induction. The induced electromotive force (e.m.f.) depends on a time-varying magnetic flux linkage ($\phi$):
$$e = -\frac{d\phi}{dt}$$ For closed circulating current paths to form inside a bulk conductor, the magnetic field passing through its volume must be actively changing over time ($\frac{d\phi}{dt} \neq 0$).

Step 3: Detailed Explanation:
Let's evaluate the behavior of each scenario:
Options (A) and (B) involve a steadymagnetic field. Because the field is static over time, the net magnetic flux is constant ($\frac{d\phi}{dt} = 0$), meaning zero induction takes place. Option (C) passes a steady current through a loop, which produces a stable, non-changing magnetic field, leading to no induction in nearby materials.
Option (D) features a bulk metal plate exposed to a varyingmagnetic field. This time-dependent variation creates a changing flux across the solid material, inducing localized swirling loops of electrical current throughout its volume. These are precisely defined as eddy currents.

Step 4: Final Answer:
Eddy currents are produced when a thick metal plate is kept in a varying magnetic field, which matches option (D).