Semiconductor Electronic: Material, Devices And Simple Circuits — Physics STD 12 Science — Question

The wavelength of X-rays is of the order of

(a) Centimetre

(b) Micron (10-6 m)

(c) Angstrom (10-10 m)

(d) Metre

When photon of energy 4.25 eV strike the surface of a metal A, the ejected photoelectrons have maximum kinetic energy T_A eV and de-Brolie wavelength . The maximum kinetic energy of photoelectrons liberated from another metal B by photon of energy 4.70 eV is   If the de-Broglie wavelength of these photoelectrons is  , then

(a) The work function of A is 2.25 eV	(b) The work function of B is 4.20 eV
(c)	(d)

Ozone layer protects us from which harmful radiations coming from the sun?

The drift current in a p-ri junction is:

A very long bar magnet is placed with its north pole coinciding with the centre of a circular loop carrying as electric current i. The magnetic field due to the magnet at a point on the periphery of the wire is B. The radius of the loop is a. The force on the wire is:

The radius of a soap bubble whose potential is 16V is doubled. The new potential of the bubble will be

(a) 2V

(b) 4V

(c) 8V

(d) 16V

Assertion  :  Thin films such as soap bubble or a thin layer of  oil on water show beautiful colours when illuminated by white light.

 Reason     : It happens due to the interference of light reflected from the upper surface of the thin film.

(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.

A point charge of 40 stat coulomb is placed 2 cm in front of an earthed metallic plane plate of large size. Then the force of attraction on the point charge is

(a) 100 dynes

(b) 160 dynes

(c) 1600 dynes

(d) 400 dynes

Electric potential is equal to :

In the circuit shown in Fig. initially key K₁ is closed and key K₂ is open. Then K₁ is opened and K₂ is closed (order is important). [Take Q₁' and Q₂' as charges on C₁ and C₂ and V₁ and V₂ as voltage respectively.]

 

Then