Explanation:
When we replace a circular current-carrying loop with a magnetic dipole to resemble field lines of the circular loop, the pole strength m and the distance between the poles are not fixed.
But the magnetic dipole moment of both systems is always fixed. It is the product of the magnetic moment and the distance between the poles. In other words, md is fixed.
A current loop of area A and current I can be replaced with a magnetic dipole of dipole moment md.
i.e. md = IA
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Between the plates of a parallel plate condenser, a plate of thickness 
and dielectric constant 
is placed. In the rest of the space, there is another plate of thickness 
and dielectric constant 
. The potential difference across the condenser will be
|
(a) |
(b) |
(c) |
(d) |
A rectangular coil of 300 turns has an average area of average area of 25 cm × 10 cm. The coil rotates with a speed of 50 cps in a uniform magnetic field of strength 4 
about an axis perpendicular of the field. The peak value of the induced e.m.f. is (in volt)
|
(a) 3000 π |
(b) 300 π |
(c) 30 π |
(d) 3 π |
Assertion : If two long wires, hanging freely are connected to a battery in series, they come closer to each other.
Reason : Force of attraction acts between the two wires carrying current.
|
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. |
|
(b) If both assertion and reason are true but reason is not the correct explanation of the assertion. |
|
(c) If assertion is true but reason is false. |
|
(d) If the assertion and reason both are false. |
A current of 5 ampere is flowing in a wire of length 1.5 metres. A force of 7.5 N acts on it when it is placed in a uniform magnetic field of 2 Tesla. The angle between the magnetic field and the direction of the current is
|
(a) 30° |
(b) 45° |
(c) 60° |
(d) 90° |
The rate of disintegration of fixed quantity of a radioactive element can be increased by
|
(a) Increasing the temperature |
(b) Increasing the pressure |
|
(c) Chemical reaction |
(d) It is not possible |
When radiation is incident on a photoelectron emitter, the stopping potential is found to be 9 volts. If e/m for the electron is 1.8 
the maximum velocity of the ejected electrons is
|
(a) 6 |
(b) 8 |
(c) 1.8 |
(d) 1.8 |
