Atoms — Physics STD 12 Science — Question

An electron is ejected from the surface of a long, thick straight conductor carrying a current, initially in a direction perpendicular to the conductor. The electron will:

A small bar magnet of moment M is placed in a uniform field H. If magnet makes an angle of 30° with field, the torque acting on the magnet is

(a) MH

(b)

(c)

(d)

Which group among the following is insulator?

A particle moves in a circular path with a continuously increasing speed. Its motion is:

1. Periodic.
2. Oscillatory.
3. Simple harmonic.
4. None of them.

Two lenses are placed in contact with each other and the focal length of combination is 80 cm. If the focal length of one is 20 cm, then the power of the other will be

(a) 1.66 D

(b) 4.00 D

(c) –1.00 D

(d) – 3.75 D

Two lithium nuclei in a lithium vapour at room temperature do not combine to form a carbon nucleus because:

1. A lithium nucleus is more tightly bound than a carbon nucleus.
2. Carbon nucleus is an unstable particle.
3. It is not energetically favourable.
4. Coulomb repulsion does not allow the nuclei to come very close.

Binding energy of a nucleus is of the order of.

A small lamp is hung at a height of 8 feet above the centre of a round table of diameter 16 feet. The ratio of intensities of illumination at the centre and at points on the circumference of the table will be

(a) 1 : 1

(b) 2 : 1

(c) 2

(d) 3 : 2

A coil and a bulb are connected in series with a dc source, a soft iron core is then inserted in the coil. Then

(a) Intensity of the bulb remains the same	(b) Intensity of the bulb decreases
(c) Intensity of the bulb increases	(d) The bulb ceases to glow