Explain why, a ringing bell suspended in a vacuum chamber cannot be heard outside.

Explain why a door cannot be opened when force is applied at the hinges.

(a) Define magnetic field lines. Describe an activity to draw a magnetic field line outside a bar magnet from one pole to another pole. (b) Explain why, a freely suspended magnet always points in the north-south direction.

We have learnt that vibration is necessary for producing sound. Explain why the sound produced by every vibrating body cannot be heard by us?

A silver balll is suspended by a string in a vacuum chamber and ultraviolet light of wavelength 2000 Å is directed at it. What electrical potential will the ball acquire as a result? Work function of silver is 4.3 eV.

A spherical ball of radius 1cm coated with a metal having emissivity 0.3 is maintained at 1000 K temperature and suspended in a vacuum chamber whose walls are maintained at 300 K temperature. Find rate at which electrical energy is to be supplied to the ball to keep its temperature constant.

Assertion (A): A bell ringing in an evacuated jar cannot be heard. Reason (R) : Sound waves in a gas are longitudinal