Ray Optics and Optical Instruments — Physics STD 12 Science — Question

At a certain place a magnet makes 30 oscillations per minute. At another place where the magnetic field is double, its time period will be

(a) 4 sec

(b) 2 sec

(c)

(d)

Inversion temperature of a thermocouple is the temperature of the hot junction at which the emf is:

In a movie hall, the distance between the projector and the screen is increased by 1% illumination on the screen is

(a) Increased by 1%

(b) Decreased by 1%

(c) Increased by 2%

(d) Decreased by 2%

The electric intensity due to an infinite cylinder of radius R and  having charge q per unit length at a distance r(r > R) from its axis is

(a) Directly proportional to	(b) Directly proportional to
(c) Inversely proportional to r	(d) Inversely proportional to

In the thunderstorm, the charges accumulate near the upper edges of clouds are:

The ratio of electric force and gravitational force acting between two charges is in the order of :

An electron and a proton are at a distance of 1. The moment of this dipole will be (C  X m)

(a) 1.6

(b) 1.6

(c) 3.2

(d) 3.2

When the key K is pressed at time  t = 0, which of the following statements about the current I in the resistor AB of the given circuit is true

(a) I = 2 mA  at all t

(b) I oscillates between 1 mA and 2mA

(c) I = 1 mA at all t

(d) At t = 0 , I = 2 mA and with time it goes to 1 mA

A charged particle of mass 0.003 gm is held stationary in space by placing it in a downward direction of electric field of  6 . Then the magnitude of the charge is

(a) 5

(b) 5

(c) -18

(d) -5

Assertion :   Charge is quantized

Reason    : Charge, which is less than 1 C is not possible

(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.