A place where the vertical component of the earth's magnetic field is zero has angle of dip is

• 45°

• 90°

• 0°

• 60°

The magnetic moment of a short bar magnet is 4 Am² . The magnetic induction at a point 10 cm away from its  mid point on axial line is B₁ , and on the equatorial line is B₂ , then

• B₁ = 8 × 10^-4 T , B₂ = 4 × 10^-4 T

• B₁ = 2 × 10^-4 T , B₂ = 1 × 10^-4 T

• B₁ = 10 × 10^-4 T , B₂ = 5 × 10^-4 T

• B₁ = 6 × 10^-4 T , B₂ = 3 × 10^-4 T

The value of angle of dip is zero at the magnetic equator because on it

• V and H are equal

• the value of V is zero

• the value of H is zero

• the value of V is infinity

A bar magnet has a coercivity of 4 x 10³ Am^-1. It is placed inside a solenoid of length 12 cm having 60 turns in order to demagnetise it. The amount of current that should be passed through the solenoid is

• 16 A

• 8 A

• 4 A

• 2 A

A bar magnet of length l and magnetic dipole moment M is bent in the form of an arc as shown in figure. The new magnetic dipole moment will be

• $\frac{\mathrm{M}}{2}$

• M

• $\frac{3\mathrm{M}}{\mathrm{\pi }}$

• $\frac{2\mathrm{M}}{\mathrm{\pi }}$

The figure illustrates how the flux density B inside a sample of demagnetised ferromagnetic material varies with the magnetic flux density B₀ , in which the sample is kept. For the sample to be suitable for making a permanent magnet, then which statement is true for this?

• OQ should be large, OR should be small

• both OQ and OR should be large

• OQ should be small and OR should be large

• both OQ and OR should be small

A frog can be levitated in magnetic field produced by a current in a vertical solenoid placed below the frog. This is possible because the body of the frog behaves as

• paramagnetic

• diamagnetic

• ferromagnetic

• anti-ferromagnetic

The magnetic susceptibility of a material of a rod is 499. The absolute permeability of vacuum is 4$\mathrm{\pi }$ x 10^-7 Hm^-1 .  The absolute permeability of the material of rod is

• $\mathrm{\pi } \times {10}^{-4} {\mathrm{Hm}}^{-1}$

• $2\mathrm{\pi } \times {10}^{-4} {\mathrm{Hm}}^{-1}$

• $3\mathrm{\pi } \times {10}^{-4} {\mathrm{Hm}}^{-1}$

• $4\mathrm{\pi } \times {10}^{-4} {\mathrm{Hm}}^{-1}$

109.

At a certain place, the horizontal component of earth's magnetic field is $\sqrt{3}$ times the vertical component. The angle of dip at that place is

• 30°

• 60°

• 45°

• 90°

Magnetic field intensity H at the centre of a circular loop of radius r carrying current I emu is 

• $\frac{\mathrm{r}}{\mathrm{I}} \mathrm{oersted}$

• $\frac{2\mathrm{\pi I}}{\mathrm{r}} \mathrm{oersted}$

• $\frac{\mathrm{I}}{2\mathrm{\pi r}} \mathrm{oersted}$

• $\frac{2\mathrm{\pi r}}{\mathrm{I}} \mathrm{oersted}$