Atoms — Physics STD 12 Science — Question

In a nuclear reaction, which of the following is conserved

(a) Atomic number

(b) Mass number

(c) Atomic number, mass number and energy

(d) None of these

The plane surface of a plano-convex lens of focal length f is silvered. It will behave as

(a) Plane mirror	(b) Convex mirror of focal length 2
(c) Concave mirror of focal length f/2	(d) None of the above

Two solenoids have identical geometrical construction but one is made of thick wire and the other of thin wire. Which of the following quantities are different for the two solenoids?

On increasing the temperature of a conductor, its resistance increases because

(a) Relaxation time decreases	(b) Mass of the electrons increases
(c) Electron density decreases	(d) None of the above

A 4 μF  condenser is connected in parallel to another condenser of 8 μF. Both the condensers are then connected in series with a 12 μF  condenser and charged to 20 volts. The charge on the plate of 4 μF condenser is

(a) 3.3 μC

(b) 40 μC

(c) 80 μC

(d) 240 μC

A wire of length L metre carrying a current of I ampere is bent in the form of a circle. Its magnitude of magnetic moment will be

(a)

(b)

(c)

(d)

The mobility of free electron is greater than that of free holes because

(a) The carry negative charge

(b) They are light

(c) They mutually collide less

(d) They require low energy to continue their motion

If the electric flux entering and leaving an enclosed surface respectively is   and   the electric charge inside the surface will be

(a) (  + )

(b) (- )

(c) (   + )/

(d) ( -   )/

Four capacitors are connected as shown in the equivalent capacitance between the points P and Q is

(a) 4 μF

(b)

(c)

(d)

Two metal spheres of capacitance   and  carry some charges. They are put in contact and then separated. The final charges  and   on them will satisfy

(a)

(b)

(c)

(d)