31.

Name two factors on which the heat energy liberated a body depend.

A lens forms an upright and diminished image of an object when the object is placed at the focal point of the given lens.
(i) Name the lens.
(ii) Draw a ray diagram to show the image formation.

A ray of light travels from water to air as shown in the diagram given below:

(i) Copy the diagram and complete the path of the way. Given the critical angle for water is 48^o.
(ii) State the condition so that internal reflection occurs in the above diagram.

The diagram below shows a point source P inside a water container. Four rays A, B, C, D starting from the source P are shown upto the water surface.

(i) Show in the diagram the path of these rays after striking the water surface.
The Critical Angle for water air surface is 48o
(ii) Name the phenomenon which the rays B and D exhibit.

Name the factor that determines:
Loudness of the sound heard.

Name the factor that determines:
A quality of the note.

Name the factor that determines:
Pitch of the note.

 What are damped vibrations?

Give one example of damped vibrations.

Name the phenomenon that causes a loud sound when the stem of a vibrating tuning fork is kept pressed on the surface of a table.