Board exam

A diamagnetic substance is brought near the north or south pole of a bar magnet. It will be :

1. Arepelled by both the poles.
2. Battracted by both the poles.
3. Crepelled by the north pole and attracted by the south pole.
4. Dattracted by the north pole and repelled by the south pole.

A circular coil of radius 8·0 cm and 40 turns is rotated about its vertical diameter with an angular speed of 25/π rad s⁻¹ in a uniform horizontal magnetic field of magnitude 3·0 × 10⁻² T. The maximum emf induced in the coil is :

1. A0·12 V
2. B0·15 V
3. C0·19 V
4. D0·22 V

Hydrogen atom initially in the ground state, absorbs a photon which excites it to n = 5 level. The wavelength of the photon is :

1. A975 nm
2. B740 nm
3. C523 nm
4. D95 nm

When an intrinsic semiconductor is doped with a small amount of trivalent impurity, then :

1. Aits resistance increases.
2. Bit becomes a p-type semiconductor.
3. Cthere will be more free electrons than holes in the semiconductor.
4. Ddopant atoms become donor atoms.

In the energy-band diagram of n-type Si, the gap between the bottom of the conduction band EC and the donor energy level ED is of the order of :

1. A10 eV
2. B1 eV
3. C0·1 eV
4. D0·01 eV

Assertion (A) : When a bar of copper is placed in an external magnetic field, the field lines get concentrated inside the bar. Reason (R) : Copper is a paramagnetic substance.

1. ABoth Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
2. BBoth Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
3. CAssertion (A) is true, but Reason (R) is false.
4. DAssertion (A) is false and Reason (R) is also false.

Assertion (A) : The phase difference between any two points on a wavefront is zero. Reason (R) : All points on a wavefront are at the same distance from the source and thus oscillate in the same phase.

1. ABoth Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
2. BBoth Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
3. CAssertion (A) is true, but Reason (R) is false.
4. DAssertion (A) is false and Reason (R) is also false.