Question

A coil is placed in a magnetic field \(\vec{B}\) as shown below :
 
A current is induced in the coil because \(\vec{B}\) is : 
 

• A. outward and increasing with time
• B. outward and decreasing with time
• C. parallel to the plane of coil and increasing with time
• D. parallel to the plane of coil and decreasing with time

Hint:

If the induced field supports the original field, the flux is decreasing. If it opposes the original field, the flux is increasing.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
According to Lenz's Law, the direction of induced current is such that it opposes the change in magnetic flux that produced it.
Step 2: Detailed Explanation:
1. The diagram shows the external magnetic field \(\vec{B}\) as dots (\(\odot\)), which means it is directed outward (towards the viewer).
2. The induced current is shown as anti-clockwise.
3. Using the right-hand thumb rule, an anti-clockwise current produces an induced magnetic field that is also directed outward.
4. Since the induced field is in the same direction as the external field, it must be trying to compensate for a decrease in the external outward flux.
5. Therefore, the external field \(\vec{B}\) must be outward and decreasing with time.
Step 3: Final Answer:
The field is outward and decreasing with time.