The speed of sound in a medium is 1200m/s. If the wavelength of the sound is 15.5m, calculate the frequency of the sound
Answers
Answer:
Explanation:
Green Science 9 Final PDF (2076)
12. Critical angle for a certain medium can be defined as the angle of incidence in a
denser medium when the corresponding angle of refraction in rarer medium
becomes 90°.
13. When the angle of incidence in a denser medium is more than the critical angle,
the ray of light reflects in the same medium. This process is called total internal
reflection of light.
14. Mirage is an optical illusion which can be observed as if there is a pond on hot
desert or coal-tarred road.
15. A mirage is formed when an inverted image of the distant object is formed on the
desert or coal-tarred road.
16. When the sunlight passes through a prism, it splits into seven colours. This process
is called dispersion of light.
17. The major cause of dispersion of light is the difference in speed of light of different
colours in the same medium. The speed of different colours in glass medium is
different.
18. The wave which is not affected by electric field and magnetic field is called
electromagnetic wave.
19. Electromagnetic waves can propagate through vacuum or without medium.
Sunlight is an example of electromagnetic wave.
20. X-rays are harmful rays for human beings having wavelength from 0.01nm to 10
nm. They cannot penetrate through bones but can easily penetrate through skin
and muscle.
21. X-rays are used to know about fracture and cracks in bones. They are used in
radiotherapy.
22. Ultraviolet rays are commonly known as UV-rays. They are harmful rays having
wave length between 10nm to 400 nm.
Sequential General Exercise 1
1. Choose the best answer from the given alternatives.
a. The critical angle for glass medium is ..................
49° 24° 42° 50°
b. When sunlight passes through a glass prism, it splits into .............. colours.
five seven three two
c. Which of the rays has the maximum wave length?
gamma rays X-rays microwave radio wave
d. The waves which are used for transmission of television are ..............
radio waves microwaves infrared rays X-rays
GREEN Science (Physics) Book-9 101
2. Answer the following questions.
a. What is light?
b. What are the sources of light? Give any three examples.
c. Define refraction of light. Draw a figure showing this process.
d. Define the following:
i. Incident ray
ii. Refracted ray
iii. Denser medium
iv. Rarer medium
e. State the laws of refraction of light.
f. Write down the cause of refraction of light.
g. What is angle of incidence?
h. What is angle of refraction?
i. What is refractive index?
j. Write down the formula to calculate refractive index.
k. What is critical angle?
l. Write down the value of critical angle for glass, water and ice.
m. What is total internal reflection of light?
n. What is mirage? How is it formed?
o. What is dispersion of light? Draw a neat figure showing this process.
p. Write down the cause of dispersion of light.
q. What are electromagnetic waves?
r. Write down the uses of X-rays and UV-rays.
3. Give reason.
a. A pencil appears bent when it is half-immersed in water.
b. Diamond sparkles in dim light.
c. Light bends when it passes form one medium to another.
d. The depth of a pond appears less than its real depth.
e. X-rays are harmful for human health.
4. Differentiate between.
a. Incident ray and refracted ray
b. Denser medium and rarer medium
c. X-rays and UV-rays
102 GREEN Science (Physics) Book-9
5. Complete the given figures.
a. b.
c. d. 49°
Water
42°
Glass
e. f.
90°
90°
6. Draw a neat and labelled figure showing
a. Total internal reflection of light
b. Dispersion of light
7. A rainbow is seen in a rainy day. Describe its reason.
8. Numerical Problems
a. The velocity of light in air is 3 × 108 m/s, calculate the velocity of light when it
enters water. The refractive index of water is 1.33. [Ans: 2.25 × 108 m/s]
b. The refraction index of water is 4/3. If the apparent depth of water in pond is 4m,
calculate the real depth. [Ans: 5.32 m]
c. The refractive index of glass is 1.5. Calculate the value of critical angle. [Ans: 42°]
d. The real depth of a pond is 5.32 m and its apparent depth is 4m. Calculate the
refractive index. [Ans: 1.33]
e. A ray of light is passing through a medium making an angle of 45°. If the
refractive index of the medium is 1.4, calculate the angle of refraction. [Ans: 30°]