Nuclei — Physics STD 12 Science — Question

The idea of secondary wavelets for the propagation of a wave was first given by

(a) Newton

(b) Huygen

(c) Maxwell

(d) Fresnel

A charge q is placed at the centre of the open end of a cylindrical vessel (figure). The flux of the electric field through the surface of the vessel is:

The power rating of an electric motor which draws a current  of 3.75 amperes when operated at 200 V is about

(a) 1 H.P.

(b) 500 W

(c) 54 W

(d) 750 H.P.

The cause of the potential barrier in a P-N diode is

(a) Depletion of positive charges near the junction

(b) Concentration of positive charges near the junction

(c) Depletion of negative charges near the junction

(d) Concentration of positive and negative charges near the junction

The de-Broglie wavelength of a neutron at 27^oC is l. What will be its wavelength at 927^oC

(a) l / 2

(b) l / 3

(c) l / 4

(d) l / 9

A radio transmitter radiates 1 kW power at a wavelength 198.6 metres. How many photons does it emit per second

(a)

(b)

(c)

(d)

Assertion   :   In practical application, power rating of resistance is not important.

Reason      : Property of resistance remain same even at high temperature.

(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.

The V-i graph for a conductor at temperature   and   are as shown in the figure. ( is proportional to

(a) cos2θ

(b) sin θ

(c) cot 2θ

(d) tan θ

A coil develops heat of 800 cal/sec. When 20 volts is applied across its ends. The resistance of the coil is (1 cal = 4.2 joule)

(a) 1.2 Ω

(b) 1.4 Ω

(c) 0.12 Ω

(d) 0.14 Ω

 Which among the following has a frequency range of 500 kHz to 1000 MHz?