Wave Optics — Physics STD 12 Science — Question

The potential at a distance R/2 from the centre of a conducting sphere of radius R will be

(a) 0

(b)

(c)

(d)

A conductor has 14.4 ×  coulombs positive charge. The conductor has (Charge on electron = 1.6  

(a) 9 electrons in excess	(b) 27 electrons in short
(c) 27 electrons in excess	(d) 9 electrons in short

A convex lens of focal length 12 cm is made of glass of μ = . What will be its focal length when immersed in liquid of μ =  

(a) 6 cm

(b) 12 cm

(c) 24 cm

(d) 30 cm

The radioactivity of a certain radioactive element drops to 1/64 of its initial value in 30 seconds. Its half life is

(a) 2 seconds

(b) 4 seconds

(c) 5 seconds

(d) 6 seconds

Metals getting magnetised by orientation of atomic magnetic moments in external magnetic field are called:

In human eye the focussing is done by

(a) To and fro movement of eye lens

(b) To and fro movement of the retina

(c) Change in the convexity of the lens surface

(d) Change in the refractive index of the eye fluids

A 6kHz sinusoidal voltage is applied to a series RC circuit. The frequency of the voltage across the resistor is.

Which of the following statement best describe Nuclear fusion reaction ?

A concave lens of focal length 20 cm placed in contact with a plane mirror acts as a

(a) Convex mirror of focal length 10 cm

(b) Concave mirror of focal length 40 cm

(c) Concave mirror of focal length 60 cm

(d) Concave mirror of focal length 10 cm