31.

Two charged spheres separated by a distance 'd' exert some force on each other. If they are immersed in a liquid of dielectric constant 2, then what is the force exerted, if all other conditions are same?

• F/2

• F

• 2F

• 4F

A steady current flows in a metallic conductor of non-uniform cross-section. Which of these quantities is constant along the conductor?

• Electric field

• Drift velocity

• Current

• Current density

The angle of dip at a certain place where the horizontal and vertical components of the earth's magnetic field are equal is

• 30^o

• 75^o

• 60^o

• 45^o

A series resonant LCR circuit has a quality factor ( Q-factor) 0.4. If  R = 2 kΩ,  C = 0.1 μF, then the value of inductance is

• 0.1 H

• 0.064 H

• 2 H

• 5 H

On increasing the temperature of a conductor, its resistance increases because the

• relaxation time increases

• electron density decreases

• relaxation time decreases

• relaxation time remains constant

The magnetic field at the centre O of the arc shown in the figure is

• 2$\mathrm{I} \left( \sqrt{2} + \mathrm{\pi } \right) \times \frac{{10}^{-7}}{\mathrm{r}}$

• 2$\mathrm{I} \left(\sqrt{2} + \frac{\mathrm{\pi }}{4}\right) \times \frac{{10}^{-7}}{\mathrm{r}}$

• $\mathrm{I} \left(\sqrt{2} + \mathrm{\pi }\right)\times \frac{{10}^{-7}}{\mathrm{r}}$

• $\mathrm{I} \left(\sqrt{2} + \frac{\mathrm{\pi }}{4}\right) \times \frac{{10}^{-7}}{\mathrm{r}}$

Assertion:  In water, value of magnetic field decreases. 

Reason:  Water is a diamagnetic substance

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion:  The electromagnetic waves are transverse in nature.

Reason:  Waves of wavelength 10 µm are radiowave and microwave.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion:  Lines of force are perpendicular to conductor surface.

Reason:  Generally electric field is perpendicular to equipotential surface.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

Assertion:  Magnetic field is useful in producing parallel beam of charged particle. 

Reason:  Magnetic field inhibits the motion of
charged particle moving across it.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.