Physics
The presence of a magnetic field at a point can be detected by means of a:
- a strong magnet
- a solenoid
- a compass needle
- a current carrying wire.
Electro-Magnetism
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Answer
a compass needle
Reason — The presence of magnetic field at a point can be detected by means of a compass needle.
A strong magnet can produce a magnetic field, it doesn't directly detect the presence of a magnetic field. Instead, it creates its own magnetic field.
A solenoid is essentially a coil of wire, which, when current flows through it, generates a magnetic field. It also doesn't directly detect the presence of an external magnetic field. It creates its own magnetic field.
In the presence of a magnetic field, the needle of compass rests only along the direction of magnetic field. Hence, it can be used to detect the presence of a magnetic field.
A current-carrying wire does generate a magnetic field, it doesn't directly detect the presence of an external magnetic field. It's used to create magnetic fields, not to detect them.
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