Available Answers

1. 1.

   Tick the most appropriate answer.

   1. The area of the mirror from which reflection takes place is called its

   1. centre of curvature.
   2. principal axis.
   3. focal length.
   4. aperture.

   2. Which phenomenon is responsible for the twinkling of stars?

   1. reflection of light
   2. refraction of light
   3. dispersion of white light
   4. none of these

   3. Which type of thermal expansion is responsible for expansion in liquids?

   1. linear expansion
   2. superficial expansion
   3. cubical expansion
   4. cubical expansion

   4. Which of the following processes takes place only at the surface of a liquid?

   1. evaporation
   2. boiling
   3. linear expansion 
   4. cubical expansion

   5. Which of the following is a wing instrument?

   1. Guitar
   2. Flute
   3. Sitar
   4. Xylophone

   6. Which of the following is a unit of loudness?

   1. joule
   2. hertz
   3. second
   4. decibel

   7.Which of the following electrical components is used to open or close a circuit?

   1. plug
   2. switch
   3. socket
   4. electric meter
2. 2.

   Write true or false. Correct the false statements.

   1. A virtual image can be obtained on a screen.
   2. Air is optically denser medium than glass.
   3. One of the ends of an iron bridge rests on rollers to allow its thermal expansion in summer.
   4. The rate of evaporation decreases with increase in temperature.
   5. Increase in the frequency of a sound increases its loudness.
   6. A monotone sound never changes in pitch,loudness, timbre or speed.
   7. When two bodies are rubbed with each other, they get charged by induction.
   8. When a live comes in contact with a neutral wire, it results in overloading.
3. 3.

   Explain how the anomalous behaviour of water on heating and cooling protects the aquatic life.

4. 4.

   How can you classify musical instruments? Explain with the help of examples.

5. 5.

   How is pitch of a sound different from its frequency?

6. 6.

   State the law of conservation of electric charges.