31.

The angle of dip at the poles and the equator respectively are

• 30^o, 60^o

• 0^o, 90^o

• 45^o, 90^o

• 90^o, 0^o

A hexagon of side 8 cm has a charge 4 µC at each of its vertices. The potential at the centre of the hexagon is

• 2.7 × 10⁶ V

• 7.2 × 10¹¹ V

• 2.5 × 10¹² V

• 3.4 × 10⁴ V

The self-inductance of a coil having 400 turns is 10 mH. The magnetic flux through the cross-section of the coil corresponding to current 2 mA is

• 2 × 10^-5 Wb

• 2 × 10^-3 Wb

• 3 × 10^-5 Wb

• 8 × 10^-3 Wb

A 5 µF capacitor is charged by being connected to a 3 V battery. The battery is then disconnected. If the resistance of the dielectric material between the capacitor plates is 10⁹ Ω, what is the charge remaining on the capacitor 1 h after it has been disconnected ?

• 1.5 × 10^-5 C

• 7.4 × 10^-6 C

• 5.4 × 10^-6 C

• 8.4 × 10^-5 C

A coil of inductance 8 μH is connected to a capacitor of capacitance 0.02 μF To what wavelength is this circuit tuned?

• 7.54 × 10³ m

• 4.12 × 10² m

• 15.90 × 10³ m

• 7.54 × 10² m

A metallic solid sphere is placed in a uniform electric field. Which path, the lines of force follow as shown in figure?

• 1

• 2

• 3

• 4

Assertion:  An emf E is induced in a closed loop when magnetic flux is varied. The induced electric field E is not a conservative field.

Reason:  The line integral $\oint \overline{\mathrm{E}} · \overline{\mathrm{dl}}$  around the closed loop is non-zero.

• 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:  UV radiation causes photodissociation of ozone into O₂ and O, thus causing damage to the stratospheric ozone layer. 

Reason:  Ozone hole is resulting in global warming and climate change.

• 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:  Electromagnetic waves with frequencies smaller than the critical frequencies of ionosphere cannot be used for communication using sky wave propagation. 

Reason: The refractive index of the ionosphere becomes very high for frequencies higher than the critical frequency.

• 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:  When a magnetic dipole is placed in a non uniform magnetic field, only a torque acts on the dipole. 

Reason:  Force would act on dipole if magnetic field is uniform.

• 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.