Atoms — Physics STD 12 Science — Question

The rate of change of magnetic flux density through a circular coil of area 10m and number of turns 100 is 10³ Wb/ m²/ s. The value of induced emf will be.

The anode of a thermionic diode is connected to the negative terminal of a battery and the cathode to its positive terminal:

In a laboratory experiment on emission from atomic hydrogen in a discharge tube, only a small number of lines are observed whereas a large number of lines are present in the hydrogen spectrum of a star. This is because in a laboratory:

The SI unit of dipole moment is:

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

Half-life of a radioactive substance is 20 minutes. Difference between points of time when it is 33% disintegrated and 67% disintegrated is approximately

(a) 10 min

(b) 20 min

(c) 30 min

(d) 40 min

For television broadcasting, the frequency employed is normally

(a) 30-300 MHz

(b) 30-300 GHz

(c) 30-300 KHz

(d) 30-300 Hz

When  electrons are removed from a neutral metal plate,  the electric charge on it is

(a) – 1.6 C

(b) + 1.6 C

(c) 10 +19 C

(d) 10–19 C

From Maxwell’s hypothesis, a charging electric field gives rise to:

As the frequency of an ac circuit increases, the current first increases and then decreases. What combination of circuit elements is most likely to comprise the circuit?