31.

Assertion: The flash of  lightening is seen before the sound of thunder is heard. 

Reason:  Speed of sound is greater than speed of light.

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

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

• If the assertion is true but the reason is false.

• If both assertion and reason are false.

Assertion: Blue star is at high temperature than red star.

Reason: Wein's displacement law states that T  ∝  ( 1/λ_m ).

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

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

• If the assertion is true but the reason is false.

• If both assertion and reason are false.

Assertion:  The time-period of pendulum, on a satellite orbiting the earth is infinity. 

Reason:  Time-period of a pendulum is inversely  proportional to  $\sqrt{\mathrm{g}}$

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

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

• If the assertion is true but the reason is false.

• If both assertion and reason are false.

Assertion: Stress is the internal force per unit area of a body.

Result: Rubber is more elastic than steel.

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

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

• If the assertion is true but the reason is false.

• If both assertion and reason are false.

Assertion:  The earth without its atmosphere would be inhospitably cold.

Reason: All heat would escape in the absence of atmosphere.

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

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

• If the assertion is true but the reason is false.

• If both assertion and reason are false.

Assertion: In simple harmonic motion, the motion is  to and fro and periodic.

Reason: Velocity of the particle  ( v)  = ω$\sqrt{{\mathrm{k}}^2 - {\mathrm{x}}^2}$ ( where x is the displacement ).

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

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

• If the assertion is true but the reason is false.

• If both assertion and reason are false.

Assertion: Woolen clothes keep the body warm in winter.

Reason:  Air is a bad conductor of heat.

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

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

• If the assertion is true but the reason is false.

• If both assertion and reason are false.

Length cannot be measure by

• fermi

• micron

• debye

• light year

An electron having charge 'e' and mass m is moving in a uniform electric field E. Its acceleration will be

• $\frac{{\mathrm{e}}^2}{\mathrm{m}}$

• $\frac{\mathrm{eE}}{\mathrm{m}}$

• $\frac{{\mathrm{eE}}^2}{\mathrm{m}}$

• $\frac{\mathrm{mE}}{\mathrm{e}}$

In the given figure, the capacitance C₁,  C₃,  C₄ and  C₅ have  a capacitance 4 μF each. If the capacitor  C₂ has a capacitance 10 μF, then effective capacitance between A and B will be

• 2 μF

• 6 μF

• 4 μF

• 8 μF