Electric Charges and Fields — Physics STD 12 Science — Question

To reduce the ripples in a rectifier circuit with capacitor filter:

A dielectric slab is inserted between the plates of a capacitor. The charge on the capacitor is Q and the magnitude of the induced charge on each surface of the dielectric is Q':

1. Q' may be larger than Q.
2. Q' must be larger than Q.
3. Q' must be equal to Q.
4. Q' must be smaller than Q.

The radius of the convex surface of plano-convex lens is 20 cm and the refractive index of the material of the lens is 1.5. The focal length of the lens is

(a) 30 cm

(b) 50 cm

(c) 20 cm

(d) 40 cm

Assertion  :  When a tiny circular obstacle is placed in the path of light from some distance, a bright spot is seen at the centre of shadow of the obstacle.

Reason      : Destructive interference occurs at the centre of the shadow.

(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 radius of circular path of an electron when subjected to a perpendicular magnetic field is

(a)

(b)

(c)

(d)

An optically active compound

(a) Rotates the plane polarised light

(b) Changing the direction of polarised light

(c) Do not allow plane polarised light to pass through

(d) None of the above

If the external force acting on a system have zero resultant, the centre of mass:

1. Must not move.
2. Must not accelerate.
3. May move.
4. May accelerate.

The age of universe is believed to be

(a) 1 billion years

(b) 10 billion years

(c) 10-20 billion years

(d) 1000 billion years