The BH curve for a ferromagnetic material is shown in the figure. The material is placed inside a long solenoid which contains 1000 turns/cm. The current that should be passed in the solenoid to demagnetize the ferromagnet completely is _____.

(a)

1.00 m A

(b)

1.25 mA

(c)

1.50 mA

(d)

1.75 mA

Two short bar magnets have magnetic moments 1.20 Am² and 1.00 Am² respectively. They are kept on a horizontal table parallel to each other with their north poles pointing towards south. They have a common magnetic equator and are separated by a distance of 20.0 cm. The value of the resultant horizontal magnetic induction at the mid-point O of the line joining their centres is (Horizontal components of Earth’s magnetic induction is 3.6 × 10^–5 Wb m^–2 )

(a)

3.60 × 10^-5 Wb m^-2

(b)

3.5 × 10^-5 Wb m^-2

(c)

2.56 × 10^-4 Wb m^-2

(d)

2.2 × 10^-4 Wb m^-2

The vertical component of Earth’s magnetic field at a place is equal to the horizontal component. What is the value of angle of dip at this place?

(a)

30° 

(b)

45° 

(c)

60° 

(d)

90° 

A flat dielectric disc of radius R carries an excess charge on its surface. The surface charge density is σ. The disc rotates about an axis perpendicular to its plane passing through the center with angular velocity ω. Find the magnitude of the torque on the disc if it is placed in a uniform magnetic field whose strength is B which is directed perpendicular to the axis of rotation.

(a)

\(\frac { 1 }{ 4 } \sigma \omega \pi BR\)

(b)

\(\frac { 1 }{ 2 } \sigma \omega \pi B{ R }^{ 2 }\)

(c)

\(\frac { 1 }{ 4 } \sigma \omega \pi B{ R }^{ 3 }\)

(d)

\(\frac { 1 }{ 4 } \sigma \omega \pi B{ R }^{ 4 }\)

A simple pendulum with charged bob is oscillating with time period T and lets θ be the angular displacement. If the uniform magnetic field switched ON in a direction perpendicular to the plane of oscillation then ___________.

(a)

time period will decrease but θ will remain constant

(b)

time period remain constant but θ will decrease

(c)

both T and θ will remain the same

(d)

both T and θ will decrease

A moving coil galvanometer shows a deflection of 10° for a current of 0.7 mA. For another current, if the deflection is 15°, then the value of current is ______

(a)

10.5 mA

(b)

1.05 mA

(c)

0.35 mA

(d)

3.5 mA

If the galvanometer constant is 0.15 A rad^-1, then the deflection for a current of 10 mA is about ______.

(a)

6°

(b)

0.1°

(c)

1°

(d)

3°

A galvanometer can be converted into a voltmeter by connecting _________________.

(a)

a low resistance in parallel to it

(b)

a high resistance in parallel to it

(c)

a low resistance in series with it

(d)

a high resistance in series with it

The unit of Galvanometer constant is ________

(a)

Am^-1

(b)

A rad^-1

(c)

AC^-1

(d)

As^-1

The voltage sensitivity of a galvanometer can be increased by _______

(a)

increasing the current

(b)

increasing the couple per unit twist of the suspension wire

(c)

increasing the number of turns of the coil

(d)

increasing the magnetic induction

Permanent magnets

(1)

To find the polarity of the solenoid

Right hand thumb rule

(2)

Steel, Alnico

Maxwell's right hand cork screw rule

(3)

Applied for circular coil carrying current

Right hand palm rule

(4)

To find the direction of magnetic field

End rule

(5)

Applied for solenoids