Electromagnetic Waves — Physics STD 12 Science — Question

A radioactive substance has a half-life of 1 year. The fraction of this material, that would remain after 5 years will be

(a)

(b)

(c)

(d)

The radius of a circular loop is r and a current i  is flowing in it. The equivalent magnetic moment will be

(a) ir

(b) 2πir

(c) iπ

(d)

Assertion : Only microwaves are used in radar.

Reason    : Because microwaves have very small wavelength.

(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 nuclear reaction   A denotes

(a) Electron

(b) Positron

(c) Proton

(d) Neutron

Resistances  and  are joined in parallel and a current is passed so that the amount of heat liberated is  and   respectively. The ratio   has the value

(a)

(b)

(c)

(d)

Which of the following phenomena suggests the presence of electron energy levels in atoms

(a) Radio active decay	(b) Isotopes
(c) Spectral lines	(d) a -particles scattering

The potential difference between the cathode and the target in a Collidge tube is 100 kV. The minimum wavelength of the X-rays emitted by the tube is

(a) 0.66 Å

(b) 9.38 Å

(c) 0.246 Å

(d) 0.123 Å

In nuclear fission the percentage of mass converted into energy is about

(a) 10%

(b) 0.01%

(c) 0.1%

(d) 1%

How much kinetic energy will be gained by an α - particle in going from a point at 70 V  to another point at 50 V

(a) 40 eV

(b) 40 keV

(c) 40 MeV

(d) 0 eV

When stopping potential is applied in an experiment on photoelectric effect, no photocurrent is observed. This means that:

1. The emission of photoelectrons is stopped.
2. The photoelectrons are emitted but are reabsorbed by the emitter metal.
3. The photoelectrons are accumulated near the collector plate.
4. The photoelectrons are dispersed from the sides of the apparatus.