A coil of self-inductance $L$ is connected in series with a bulb and an a. c. source. Brightness of the bulb decreases when

The period of S. H.M. of a particle is 16 second. The phase difference between the positions at $\mathrm{t}=2 \mathrm{~s}$ and $\mathrm{t}=4 \mathrm{~s}$ will be

A body cools from $60^{\circ} \mathrm{C}$ to $40^{\circ} \mathrm{C}$ in 6 minutes. After next 6 minutes its temperature will be (Temperature of the surroundings is $10^{\circ} \mathrm{C}$ )

A parallel beam of light is incident normally on a plane surface absorbing $50 \%$ of the light and reflecting the rest. If the incident beam carries 90 W of power, the force exerted by it on the surface is ( $\mathrm{C}=$ velocity of light in air $=3 \times 10^8 \mathrm{~m} / \mathrm{s}$ )