Your parents are going to buy a house. T | Class 8 Science Chapter Sound, Sound NCERT Solutions

List sources of noise pollution in your surroundings.

Explain in what way noise pollution is harmful to humans.

The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per second. What is the time period of the vibration?

Fill in the blanks with suitable words.
(a) Time taken by an object to complete one oscillation is called ................... .
(b) Loudness is determined by the .........................of vibration.
(c) The unit of frequency is..........................
(d) Unwanted sound is called ......................... .
(e) Shrillness of a sound is determined by the ................. of vibration.

Choose the correct answer :
Sound can travel through
(a) gases only (b) solids only
(c) liquids only (d) solids, liquids and gases.

Sketch larynx and explain its function in your own words.

What is the difference between noise and music? Can music become noise sometimes?

Which of the following voices is likely to have minimum frequency?
(a) Baby girl (b) Baby boy
(c) A man (d) A woman

A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.

Identify the part which vibrates to produce sound in the following instruments:
(a) Dholak (b) Sitar (c) Flute

Describe with the help of a diagram an instrument which can be used to detect a charged body.

Arrange the following boxes in proper order to make a flow chart of sugarcane crop production.

Make a labelled diagram of a candle flame.

What is metamorphosis? Give examples.

The following Table shows the total power shortage in India from 1991– 1997. Show the data in the form of a graph. Plot shortage percentage for the years on the Y-axis and the year on the X-axis.

Describe the construction of a kaleidoscope.

Make sketches of animal and plant cells. State three differences between them.

What is a constellation? Name any two constellations.

Complete the crossword with the help of clues given below:
Across
1. This is necessary for photosynthesis.
3. Term for component present in the cytoplasm.
6. The living substance in the cell.
8. Units of inheritance present on the chromosomes.

Down
1. Green plastids.
2. Formed by collection of tissues.
4. It separates the contents of the cell from the surrounding medium.
5. Empty structure in the cytoplasm.
7. A group of cells.

Make a sketch of the human nerve cell. What function do nerve cells perform?

How are babies produced through IVF technique? What are such babies called?

What is menstruation? Explain.

Do all the stars in the sky move? Explain.

Should the handle and bristles of a tooth brush be made of the same material? Explain your answer.

Suggest three measures to protect ourselves from lightning.

Explain how the use of CNG in automobiles has reduced pollution in our cities.

Fill in the blanks:

(a) Microorganisms can be seen with the help of a ____________.
(b) Blue green algae fix __________ directly from air to enhance fertility of soil.
(c) Alcohol is produced with the help of __________.
(d) Cholera is caused by __________.

Explain why a charged balloon is repelled by another charged balloon whereas an uncharged balloon is attracted by another charged balloon?

‘Avoid plastics as far as possible’. Comment on this advice.

Select the correct word from the following list and fill in the blanks.
                 float, water, crop, nutrients, preparation

(a) The same kind of plants grown and cultivated on a large scale at a place is called _____________.
(b) The first step before growing crops is _____________ of the soil.
(c) Damaged seeds would _____________ on top of water.
(d) For growing a crop, sufficient sunlight and _____________ and _____________ from the soil are essential.