Electromagnetic Waves — Physics STD 12 Science — Question

The number of turns in primary and secondary coils of a transformer are 100 and 300 respectively. If in- put power is 60 W, then output power will be:

The self inductance of a motor of an electric fan is 10H. In order to impart maximum power at 50Hz, it should be connected to a capacitance of:

A small coil C with N = 200 turns is mounted on one end of a balance beam and introduced between the poles of an electromagnet as shown in figure. The cross sectional area of coil is A= 1.0 cm², length of arm OA of the balance beam is l = 30 cm. When there is no current in the coil the balance is in equilibrium. On passing a current I = 22 mA through the coil the equilibrium is restored by putting the additional counter weight of mass ∆m = 60 mg on the balance pan. Find the magnetic induction at the spot where coil is located.

(a) 0.4 T

(b) 0.3 T

(c) 0.2 T

(d) 0.1 T

Two plates are 2 cm  apart, a potential difference of 10 volt  is applied between them, the electric field between the plates is

(a) 20 N/C

(b) 500 N/C

(c) 5 N/C

(d) 250 N/C

Three capacitors of capacitance 3 μF , 10 μF and 15 μF  are connected in series to a voltage source of 100V. The charge on 15 μF is

(a) 50 μC

(b) 100 μC

(c) 200 μC

(d) 280 μC

In the given circuit, it is observed that the current I is independent of the value of the resistance R₆. Then the resistance values must satisfy

(a)	(b)
(c)	(d)

Assertion   :   If three identical bulbs are connected in series as shown in figure then on closing the switches. Bulb C short circuited and hence illumination of bulbs A and B decreases.

Reason      : Voltage on A and B decreases

(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.

When the light source is kept 20 cm away from a photo cell, stopping potential 0.6 V is obtained. When source is kept 40 cm away, the stopping potential will be

(a) 0.3 V

(b) 0.6 V

(c) 1.2 V

(d) 2.4 V

An electron enters in high potential region  from lower potential region  then its velocity

(a) Will increase

(b) Will change in direction but not in magnitude

(c) No change in direction of field

(d) No change in direction perpendicular to field

In a transformer, the number of turns in primary and secondary are 500 and 2000 respectively. If current in primary is 48 A, the current in the secondary is

(a) 12 A

(b) 24 A

(c) 48 A

(d) 144 A