Question

Two identical coaxial coils P and Q carrying equal current in the same direction are brought nearer. The current in:

• A. P increases while in Q decreases
• B. Q increases while in P decreases
• C. Both P and Q increase
• D. Both P and Q decrease

Answer 1

The Correct Option is D

When two identical coaxial coils carrying equal current in the same direction are brought closer:

Key Physics Principles:

1. Mutual Induction: As the coils move closer, their mutual inductance increases.
2. Lenz's Law: The induced current opposes the change that produced it.
3. Energy Conservation: The system resists the change in configuration.

What Happens to the Current:

• As coil P approaches coil Q, the changing magnetic flux through Q induces an opposing current in Q
• Simultaneously, the changing flux through P induces an opposing current in P
• This mutual induction effect reduces current in both coils
• The closer the coils, the stronger this effect becomes

Therefore, the current in both P and Q decreases when they are brought nearer.

Visualization:

Coil P Current (→) → Induced field in Q opposes (←) → Q's current decreases
Coil Q Current (→) → Induced field in P opposes (←) → P's current decreases