Question

When two coaxial coils having the same current in the same direction are brought close to each other, then the value of current in both the coils:

• A. Increases
• B. Decreases
• C. Remains Same
• D. Increase in one coil and decrease in the other

Hint:

When two coils are brought close together, mutual induction occurs, leading to an induced EMF that opposes the current flow. This results in a decrease in the current in both coils, as explained by Lenz's Law.

Answer 1

The Correct Option is B

Step 1: Understanding Mutual Induction in Coaxial Coils When two coaxial coils carrying current in the same direction are brought close to each other, mutual inductance plays a crucial role. The changing magnetic flux due to one coil induces an opposing electromotive force (EMF) in the other coil, according to Lenz's Law. 
Step 2: Effect of Mutual Induction The induced EMF opposes the original current, causing a decrease in the current in both coils. This effect is similar to how self-inductance resists changes in current within a single coil, except here it occurs between two coupled coils. 
Step 3: Evaluating the Given Options - Increases (Incorrect): Due to Lenz’s Law, the induced EMF always opposes the change in flux, meaning it reduces the current rather than increasing it. 
- Decreases (Correct): The induced EMF works against the applied voltage, leading to a decrease in the net current in both coils. 
- Remains same (Incorrect): If there were no mutual induction, the current would remain unchanged, but since mutual induction is present, the current decreases. 
- Increases in one coil and decreases in the other (Incorrect): This does not occur in this case because the mutual inductance symmetrically affects both coils. 
Step 4: Conclusion Thus, when the two coaxial coils are brought closer together, the current in both coils decreases due to the opposing induced EMF.