General Science 7th Class Chapter 9 Waves and Energy Solved Exercise

 General Science

7th Class

Chapter 9

Waves and Energy

Questions

9.1 Encircle the correct option.

1. Sound waves are not:

a. compressional waves        b. transverse waves

c. mechanical waves        d. low frequency waves

2. Sound cannot pass through:

a. solid        b. liquid        c. gasses        d. vacuum

3. The speed of sound in air is:

a. 100 m/s        b. 340 m/s        c. 1000 m/s        d. 330 km/s

correct 300 on guide

4. Which of the following animals can respond to lowest frequency?

a. cat        b. cow        c. dog        d. elephant

5. Which of the following animals can respond to highest frequency?

a. bat        b. cat        c. frog        d. dolphin

6. Which have audible range for 2k Hz and 120k Hz?

a. human        b. owl        c. bat        d. dolphin

7. Which of the following features is the height of the wave from the rest position or midline?

a. frequency        b. amplitude        c. pitch        d. wavelength

8. Which of the following features of a wave is the number of waves that pass by each second?

a. loudness        b. amplitude        c. frequency        d. wave speed

9. What is transferred by the movement of waves?

a. matter        b. energy        c. nothing        d. both the matter and energy

10. What type of wave does not need matter to travel through?

a. mechanical        b. electromagnetic        c. sound        d. transverse

11. Which sequence of visible colour is correct from longest wavelength to short wavelength?

a. violet, indigo, blue, green, orange, yellow, red

b. red, orange, yellow, green, blue, indigo, violet

c. red, yellow, green, orange, violet, blue, indigo

d. red, yellow, green, orange, violet, indigo, blue

9.2 Define the following:

1. Wave

2. Electromagnetic wave

3. Wavelength

4. Frequency

5. Amplitude

6. Time period

1. Wave

Ans:

A wave is a disturbance or variation that transfers energy progressively from point to point in a medium.

2. Electromagnetic wave

Ans:

Waves which do not require any medium to travel through is called electromagnetic waves. Light waves are the examples of electromagnetic waves.

3. Wavelength

Ans:

Wavelength is the distance between the centres of the compressions or rarefactions of two consecutive waves.

4. Frequency

Ans:

Frequency is the number of waves produced in one second. It is equal to the number of times a body vibrates in one second. Frequency of wave is represented by "f".

5. Amplitude

Ans:

The maximum displacement of the vibrating objects from its mean position is called its amplitude. It is measured in the unit 'metre (m)'.

6. Time period

Ans:

The time during which a body completes one wave cycle is called the time period. It is represented by T.