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

When two coaxial coils carrying the same current in the same direction are brought near each other, their magnetic fields interact. According to Lenz's Law, the system will adjust to oppose this change. The mutual inductance between the coils increases due to their proximity, which affects the total magnetic field.

The specific interaction causes an induced electromotive force (EMF) in each coil. Due to Lenz's Law, this EMF opposes the original current. Thus, the overall effect is a reduction in the net current flowing in both coils.

Hence, when two coaxial coils with identical currents are brought close together, the current in both coils reduces. Therefore, the correct answer is: Decreases.

Answer 2

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.