Two identical coaxial coils P and Q carrying equal current in the same direction are brought nearer. The current in :
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Both P and Q decreases
By Lenz's law, an induced current always opposes the change in magnetic flux that produces it.
Each coil sends magnetic flux through the other, in the same direction as the coil's own flux, because the currents are in the same direction. As the coils are brought nearer, the flux through each coil increases.
To oppose this increase, the induced current in each coil flows opposite to the current already in it. So the net current falls in both coils.
The situation is the same for P and Q, so both currents change in the same way; one cannot increase while the other decreases.
NCERT (2026-27):
Lenz’s Law and Conservation of Energy – “In 1834, German physicist Heinrich Friedrich Lenz (1804-1865) deduced a rule, known as Lenz’s law which gives the polarity of the induced emf in a clear and concise fashion. The statement of the law is: The polarity of induced emf is such that it tends to produce a current which opposes the change in magnetic flux that produced it.”