Current Electricity — Physics STD 12 Science — Question

The magnetic field B with in the solenoid having n turns per metre length and carrying a current of i ampere is given by

(a)

(b)

(c) 4π

(d) ni

Some magnetic flux is changed from a coil of resistance 10 ohm. As a result an induced current is developed in it, which varies with time as shown in figure. The magnitude of change in flux through the coil in webers is

(a) 2

(b) 4

(c) 6

(d) None of these

The resistances of a wire at temperatures t℃ and 0℃  are related by

(a)

(b)

(c)

(d)

The number of turns in the primary coil of a transformer is 200 and the number of turns in the secondary coil is 10. If 240 volt AC is applied to the primary, the output from the secondary will be

(a) 48 V

(b) 24 V

(c) 12 V

(d) 6 V

According to Joule's law, if potential difference across a conductor of material of resistivity remains constant, then heat produced in the conductor is directly proportional to

Current of 1 A is flowing through two parallel wires in the same direction and distance between the wires is 1 m . The mutual attractive force at unit length will be :

Charges 4Q, q and Q and placed along x-axis at positions x = 0, x = l/2  and  x = l, respectively. Find the value of q so that force on charge Q is zero             

(a) Q

(b) Q / 2

(c) – Q / 2

(d) – Q

If a piece of metal was thought to be magnet, which one of the following observations would offer conclusive evidence

(a) It attracts a known magnet	(b) It repels a known magnet
(c) Neither (a) nor (b)	(d) It attracts a steel screw driver

Which of the following mirrors is used in searchlight?