Atoms — Physics STD 12 Science — Question

The efficiency of transformer is very high because

(a) There is no moving part in a transformer	(b) It produces very high voltage
(c) It produces very low voltage	(d) None of the above

A strip of copper and another of germanium are cooled from room temperature to 80 K. The resistance of

(a) Each of these increases

(b) Each of these decreases

(c) Copper strip increases and that of germanium decreases

(d) Copper strip decreases and that of germanium increases

Assertion  : The positively charged nucleus of an atom has a radius of almost .

Reason      : In a-particle scattering experiment, the distance of closest approach for a-particles is

(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.

What is the net magnetic flux through a closed surface?

In a sample of radioactive material, what percentage of the initial number of active nuclei will decay during one mean life

(a) 69.3%

(b) 63%

(c) 50%

(d) 37%

A metal wire of specific resistance 64   and length 198 cm has a resistance of  7 ohm, the radius of the wire will be

(a) 2.4 cm

(b) 0.24 cm

(c) 0.024 cm

(d) 24 cm

If f_a and f_f represent the carrier wave frequencies for amplitude and frequency modulations respectively, then

(a)

(b)

(c)

(d)

A galvanometer of resistance 20 W is to be converted into an ammeter of range 1 A.  If a current of 1 mA produces full scale deflection, the shunt required for the purpose is

(a) 0.01 W

(b) 0.05 W

(c) 0.02 W

(d) 0.04 W

 The rate of flow of electric charge through any cross-section of a conductor is known as __________.

The lines of forces due to earth's horizontal component of magnetic field are

(a) Parallel straight lines	(b) Concentric circles
(c) Elliptical	(d) Parabolic