Reproduction in animals — Science STD 8 — Question

Explain with the help of diagrams, how the use of oil reduces friction between two surfaces in contact with each other.

What type of combustion is represented by:

1. Burning of white phosphorus in air at room temperature?
2. Burning of LPG in a gas stove?
3. Ignition of a cracker?
4. Burning of coal dust in a coal mine?

Name the part of the eye:

1. Which controls the amount of light entering the eye.
2. Which converges light rays to form the image.
3. On which image is formed.
4. Which carries the image to brain.
5. Which changes the curvature (or thickness) of eye-lens to focus objects lying at various distances.

What is meant by the term ‘Wildlife’? Why should forests and wildlife be conserved?

How does a lightning conductor protect a tall building? Name the scientist who invented the lightning conductor.

Explain why, it is easier to drag a mat on floor when nobody is sitting on it but much more difficult to drag the same mat when a person is sitting on it.

How does a Hydra reproduce? Explain with the help of labeled diagrams.

Which of the following will cause regular reflection of light and which diffuse reflection of light?

1. Polished wooden table.
2. Chalk powder.
3. Cardboard.
4. Mirror.
5. Paper.
6. Marble floor with water spread over it.

A strip of impure copper metal is given to you. Describe briefly how you will purify it by using the chemical effect of electric current. Draw a labelled diagram of the experimental set up used for this purpose.

What is a seismograph? Draw a labelled diagram of a seismograph.