Sound Waves — Physics STD 12 Science — Question

A point source is placed at a depth h below the surface of water (refractive index = μ).

1. Show that light escapes through a circular area on the water surface with its centre directly above the point source.
2. Find the angle subtended by a radius of the area on the source.

If we put a cardboard (say 20cm × 20cm) between a light source and our eyes, we can't see the light. But when we put the same cardboard between a sound source and our ear, we hear the sound almost clearly. Explain.

Explain the process of leakage of electric charge.

Electrons are emitted from the surface when green light is incident on it, but no electrons are ejected when yellow light is incident on it. Do you expect electrons to be ejected when surface is exposed to (i) Red light and (ii) Blue light?

Ultrasonic waves of frequency 4.5MHz are used to detect tumour in soft tissues. The speed of sound in tissue is 1.5km/s and that in air is 340m/s. Find the wavelength of this ultrasonic wave in air and in tissue.

Suppose the platform of the previous problem is brought to rest with the ball in the hand of the kid standing on the rim. The kid throws the ball horizontally to his friend in a direction tangential to the rim with a speed v as seen by his friend. Find the angular velocity with which the platform will start rotating.

Explain with example why matter particle acquires electric charge.

Derive the condition of Constructive and destructive interference in terms of the phase difference.

Find the area bounded by the curve y = e^-x, the X-axis and the Y-axis.