Curie temperature is the temperature above which

• ferromagnetic material becomes paramagnetic material

• paramagnetic material becomes diamagnetic material

• paramagnetic material becomes ferromagnetic material

• paramagnetic material becomes ferromagnetic material

Above Curie temperature

• a ferromagnetic substance becomes paramagnetic

• a paramagnetic substance becomes diamagnetic

• a diamagnetic substance becomes paramagnetic

• a diamagnetic substance becomes paramagnetic

A 250-Turn rectangular coil of length 2.1 cm and width 1.25 cm carries a current of 85 μA and subjected to a magnetic field of strength 0.85 T. Work done for rotating the coil by 180° against the torque is

• 9.1 μJ

• 4.55 μJ

• 2.3 μJ

• 2.3 μJ

Figure shows a circuit contains three identical resistors with resistance R = 9.0 Ω each, two identical inductors with inductance L = 2.0 mH each, and an ideal battery with emf  ε= 18 V. The current'i' through the battery just after the switch closed is

• 2 mA

• 0 mA

• 2 A

• 2 A

55.

A thin diamagnetic rod is placed vertically between the poles of an electromagnet. When the current in the electromagnet is switched on, then the diamagnetic rod is pushed up, out of the horizontal magnetic field. Hence the rod gains gravitational potential energy. The work required to do this comes from

• The current source

• The magnetic field

• The induced electric field due to the changing magnetic field

• The lattice structure of the material of the rod

In the given figure, what is the magnetic field induction at point O.

• $\frac{{\mathrm{\mu }}_{\mathrm{o}}\mathrm{I}}{4\mathrm{\pi r}}$

• $\frac{{\mathrm{\mu }}_{\mathrm{o}}\mathrm{I}}{4\mathrm{r}} + \frac{{\mathrm{\mu }}_{\mathrm{o}} \mathrm{I}}{2\mathrm{\pi r}}$

• $\frac{{\mathrm{\mu }}_0 \mathrm{I}}{4\mathrm{r}} + \frac{{\mathrm{\mu }}_0 \mathrm{I}}{4\mathrm{\pi r}}$

• $\frac{{\mathrm{\mu }}_0 \mathrm{I} }{4\mathrm{r}} - \frac{{\mathrm{\mu }}_0 \mathrm{I}}{4\mathrm{\pi } \mathrm{r}}$

A uniform electric field and a uniform magnetic field acting along the same direction in a certain region. If an electron is projected along the direction of the fields with a certain velocity, then

• It will turn towards the left of the direction of motion.

• It will turn towards the right of the direction of motion

• Its velocity will increase

• Its velocity will decrease

 Magnetic field of a short magnet at a distance lm on axial line is 1 oersted at a distance 2 m on the same line the intensity in oersted is

• 0.75

• 0.125

• 0.25

• 0.5

The ratio of magnetic moments of two short magnets which give null deflection in tan B position at 12 cm and 18 cm from the centre of a deflection magnetometer is

• 4:9

• 27:8

• 2:3

• 8:27

The distance between the poles of horse shoe magnet is 10 cm and its pole strength is 10⁴ A. The magnetic field induction at point P mid-way between the poles is

• $8\times {10}^{-9} \mathrm{tesla}$

• 4×10^-19 tesla

• 2×10^-9 tesla

• zero