Atoms — Physics STD 12 Science — Question

A silver ball of radius 4.8 cm is suspended by a thread in the vacuum chamber. UV light of wavelength 200 nm is incident on the ball for some times during which a total energy of 1 × 10^–7 J falls on the surface. Assuming on an average one out of 10³ photons incident is able to eject electron. The potential on sphere will be

(a) 1 V

(b) 2 V

(c) 3 V

(d) Zero

Assertion : The comet do not obey Kepler's laws of planetary motion

Reason     :  The comet do not have elliptical orbit

(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.

In the circuit, the potential difference across PQ will be nearest to

(a) 9.6 V

(b) 6.6 V

(c) 4.8 V

(d) 3.2 V

The two rails of a railways track, insulated from each other and the ground, are connected to a milli voltmeter. What is the reading of the milli voltmeter when a train travels at a speed of 20 ms^-1 along the track, given that the vertical component of the earth's magnetic field is 0.2 × 10^-4 Wbm^-2 and the rails are separated by 1m?

In case of Coulomb’s law, the value of k is given by:

An object is placed at a distance u from a simple microscope of focal length f. The angular magnification obtained depends:

1. On f but not on u.
2. On u but not on f.
3. On f as well as u.
4. Neither on f nor on u.

The collector plate in an experiment on photoelectric effect is kept vertically above the emitter plate. Light source is put on and a saturation photocurrent is recorded. An electric field is switched on which has a vertically downward direction.

When objects at different distances are seen by the eye, which of the following remain constant?

1. The focal length of the eye-lens.
2. The object-distance from the eye-lens.
3. The radii of curvature of the eye-lens.
4. The image-distance from the eye-lens.

Which of the following are in the ascending order of wavelength?