Selina Concise Class 10 Physics Solution Chapter No. 6- ‘Spectrum’ For ICSE Board Students.
Selina Concise Class 10 Physics Chapter 6 Spectrum Exercise All Questions and Answers by Physics Teacher here in this post.
Exercise 6 (A)
Question: 1
Name three factors on which the deviation produced by a prism depends and state how does it depend on the factors stated by you.
Solution: The total angle of deviation depends upon the following three factors
(a) The angle of incident (i) at the surface, angle of deviation is found to be increase with increasing angle of incident.
(b) The angle of prism, angle of deviation increases with increase with angle of prism.
(c) The refractive index of the material of the prism. Higher the refractive index higher the angle of deviation.
Question: 2
How does the deviation produced by a triangular prism depend on the colour (or wavelength) of light incident on it?
Solution: As the wavelength of incident light decreases the deviation produced by prism increases.
Question: 3
How does the speed of light in glass change on increasing the wavelength of light?
Solution: The speed of light in glass increases as the wavelength of light increases.
Question: 4
Which colour of white light travels (a) fastest (b) slowest, in glass?
Solution:
(a) Red colour travels fastest in glass.
(b) Blue colour travels slowest in glass.
Question: 5
Name the subjective property of light related to its wavelength.
Solution: The subjective property of light related to its wavelength is colour of light.
Question: 6
What is the range of wavelength of the spectrum of white light in (i) A0 (ii) nm?
Solution:
(i) The range of wavelength is 4000 A0 to 8000 A0.
(ii) The range of wavelength is 400 nm to 800 nm.
Question: 7
(a) Write the approximate wavelengths for (i) blue and (ii) red light.
(b) The wavelength of violet and red light are 4000 A0 and 8000 A0 respectively. Which of the two has the higher frequency?
Solution:
(a) Wavelength of blue light is 4800 A0 and wavelength of red colour is 8000 A0.
(b) As frequency od red colour is higher.
Question: 8
Write the seven prominent colours present in white light in the order of increasing wavelength
Solution: The seven prominent colour present in white light in order of increasing wavelength are Violet, indigo, blue, green, yellow, orange and red.
Question: 9
Name the seven prominent colours of the white light spectrum in order of their increasing frequencies.
Solution: The seven prominent colour present in white light in order of increasing frequencies are red, orange, yellow, green, blue, indigo and violet.
Question: 10
Name four colours of the spectrum of white light which have wavelength longer than blue light.
Solution: Green, yellow, orange and red.
Question: 11
Which colour of the white light is deviated by a glass prism (i) the most and, (ii) the least?
Solution: As wavelength is inversely proportional to the deviation produced by prism hence red colour is least deviated and violet colour is most deviated.
Question: 12
The wavelengths for the light of red and blue colours are nearly 7.8 x 10-7m and 4.8 x 10-7 m respectively.
(a) Which colour has the greater speed in vacuum?
(b) Which colour has greater speed in glass?
Solution:
(a) Vaccum will not affect the speed of light according to colour.
(b) Red colour has greater speed in glass.
Question: 13
Define the term dispersion of light.
Solution: When beam of white light splits into its seven constituent colours when passed through a transparent medium is called as dispersion of light.
Question: 14
Explain the cause of dispersion of white light through a prism.
Solution: The speed of different wavelength of light in different transparent medium. Hence, while passing through prism colour different colours deviates through different angle because of difference in speed. Which causes dispersion of white light.
Question: 15
Explain briefly, with the help of a neat labelled diagram, how does white light get dispersed by a prism.
On which surface of a prism, there is both dispersion and deviation of light, and on which surface of the prism, there is only deviation of light?
Solution: Glass prism has the different refractive index than to air hence when light enter in glass prism the velocity of different wavelength changes accordingly and the light gets split in its component colour.
On the first surface both dispersion and deviation takes place and on second surface only deviation takes place.
Question: 16
What do you understand by the term spectrum?
Solution: When light passes through prism the band seen of dispersed light which is called as spectrum
Question: 17
A ray of white light is passed through a glass prism and spectrum is obtained on a screen.
(a) Name the seven colours of the spectrum in order.
(b) Do the colours have the same width in the spectrum?
(c) Which colour of the spectrum of white light deviates (i) the most? (ii) the least?
Solution:
(a) Violet, indigo, blue, green, yellow, orange and red
(b) Different colour has different width in spectrum.
(c) Violet colour deviates the most and red colour deviates the least.
Question: 18
The diagram shown below in Fig. shows the path taken by a narrow beam of yellow monochromatic light passing through an equiangular glass prism. If the yellow light is replaced by a narrow beam of white light incident at the same angle, draw another diagram to show the passage of white light through the prism and label it to show the effect of the prism on the white light.
Solution:
Question: 19
The figure shows a thin beam of white light from a source S striking on one face of a prism.
(a) Complete the diagram to show the effect of the prism on the beam and to show what is seen on the screen.
(b) If a slit is placed in between the prism and the screen to pass only the light of green colour. What will you then observe on the screen?
(c) What conclusion do you draw from the observation in part (b) above?
Solution:
(a) A light spectrum is seen the screen.
(b) When a monochromatic beam of light passes through the prism we only see that colour. So, on the screen only green colour is seen.
(c) Prism only refracts the light.
Question: 20
(a) A beam of monochromatic light undergoes minimum deviation through an equiangular prism. How does the beam pass through the prism, with respect to its base?
(b) If white light is used in the same way as in part (a) above, what change is expect in the emergent beam?
(c) What conclusion do you draw about the nature of white light in part (b)?
Solution:
(a) Light beam will be parallel to the base.
(b) White light will split into its spectrum.
(c) White light is made of lights with different wavelength (polychromatic).
Multiple Choice Type:
Question: 1
When a white light ray falls on a prism, the ray at its first surface suffers:
(a) No refraction
(b) only dispersion
(c) only deviation
(d) both deviation and dispersion
Solution: (d) both deviation and dispersion
Question: 2
In the spectrum of white light by a prism, the colour at the extreme end opposite to the base of prism is:
(a) Violet
(b) yellow
(c) red
(d) blue
Solution: (c) red
Question: 3
The wavelength range of white light is:
(a) 4000 nm to 8000 nm
(b) 40 nm to 80 nm
(c) 400 nm to 800 nm
(d) 4 nm to 8 nm
Solution: (c) 400 nm to 800 nm
Numerical
Question: 1
Calculate the frequency of yellow light of wavelength 550 nm. The speed of light is 3 x 108m s-1.
Solution: Given
Wavelength = 550 nm = 550 x 10-9m
Speed of light = 3 x 108m/s
Frequency = speed of light / wavelength
= 3 x 108 / 550 x 10-9m
= 5.4 x 1014m
Question: 2
The frequency range of visible light is from 3.75 x 1014 Hz to 7.5 x 1014 Hz. Calculate its wavelength range. Take speed of light = 3 x 108m s-1
Solution: Given
Frequency range = 550 nm = 3.75 x 1014 Hz to 7.5 x 1014 Hz
Speed of light = 3 x 108m/s
For frequency, 3.75 x 1014 Hz
Wavelength = speed of light / frequency
= 3 x 108m / 3.75 x 1014
= 8 x 10-7m
= 800 nm
For frequency, 7.5 x 1014 Hz
Wavelength = speed of light / frequency
= 3 x 108m / 7.5 x 1014
= 4 x 10-7m
= 400 nm
Wavelength range is 800 nm to 400 nm.
Exercise 6 (b)
Question: 1
(a) Give a list of at least five radiations, in the order of their increasing wavelength, which make up the complete electromagnetic spectrum.
(b) Name the radiation mentioned by you in part (a) which has the highest penetrating power.
Solution:
(a) Electromagnetic radiation with increasing wavelength are gamma rays, X-rays, ultraviolet rays, visible light and infrared radiation.
(b) Gamma rays has the highest penetrating power.
Question: 2
(a) Arrange the following radiations in the order of their increasing wavelength:
X-rays, infrared rays, radio waves, gamma rays and microwaves.
(b) Name the radiation which is used for satellite communication?
Solution:
(a) Radiations with increasing wavelength are gamma rays, X-rays, infrared rays, microwaves and radio waves.
(b) Microwaves are used for satellite communication.
Question: 3
A wave has a wavelength of 10-3 nm.
(a) Name the wave
(b) State its one property different from light.
Solution:
(a) Gamma rays has the wavelength of 10-3 nm.
(b) Gamma rays are more power full and high penetrating power than ligh.
Question: 4
A wave has wavelength 50 A0.
(a) Name the wave.
(b) State its speed in vacuum
(c) State its one use.
Solution:
(a) X- ray.
(b) Speed of X-ray in vaccum is 3 x 108 m/s
(c) It is used for scanning bones in medical instruments.
Question: 5
(a) Name the high energetic invisible electromagnetic wave which helps in the study of the structure of crystals.
(b) State one more use of the wave named in part (a).
Solution:
(a) X-ray is used for study of the crystals.
(b) It is used for scanning bones in medical instruments.
Question: 6
State the name and the range of wavelength of the invisible electromagnetic waves beyond the red end of the visible spectrum.
Solution: Infrared radiations which have wavelength of 8000 to 107 A0 are the radiations beyond the red end of the visible spectrum.
Question: 7
Name three radiations and their wavelength range which are invisible and beyond the violet end of the visible spectrum.
Solution: gamma rays of wavelength below 10-3nm, X-ray of wavelength 10-3 to 10 nm, ultraviolet rays of wavelength 10 to 400 nm. Are invisible and beyond the violet end of the visible spectrum.
Question: 8
Give the range of wavelength of the electromagnetic waves visible to us.
Solution: The wavelength of visible light is 4000 A0 to 8000 A0.
Question: 9
Name the region just beyond (i) the red end, and (ii) the violet end, of the spectrum.
Solution:
(i) The region beyond the red end is called as infrared region.
(ii) The region beyond the violet end is called as ultraviolet radiations.
Question: 10
What do you understand by the invisible spectrum?
Solution: The region beyond and below the visible spectrum which is not detected by the our eyes is called as invisible spectrum.
Question: 11
Name the radiation which can be detected by (a) a thermopile (b) a solution of silver chloride.
Solution:
(a) Thermopile detects X- ray radiations.
(b) A solution of silver chloride detects ultraviolet radiations.
Question: 12
State the approximate range of wavelength associated with (a) the ultraviolet rays, (b) visible light, and (c) infrared rays.
Solution:
(a) ultraviolet rays are of wavelength 10 to 400 nm
(b) visible light is of wavelength 4000 to 8000 nm.
(c) Infrared radiations are of wavelength 8000 to 107nm
Question: 13
Name the radiations of wavelength just (a) longer than 8 × 10-7 m, (b) shorter than 4 × 10-7 m
Solution:
(a) Infrared radiations
(b) Ultraviolet radiations.
Question: 14
Name two electromagnetic waves of wavelength smaller than that of violet light. State one use of each.
Solution: Gamma rays and X-rays. Gamma rays are used in cancer treatment and X-ray are used to detect fractures in the bone.
Question: 15
Give one use each of (a) microwaves, (b) ultraviolet radiations, (c) infrared radiations, and (d) gamma rays.
Solutions:
(a) microwave radiations are used for satellite communications.
(b) Ultraviolet radiation are used for detection of elements in U.V. spectrometer.
(c) Infrared radiations are used in TV remote.
(d) Gamma rays are used in cancer treatment.
Question: 16
Name the two waves (a) of lowest wavelength, (b) used for taking photographs in dark, (c) produced by the changes in the nucleus of an atom, (d) of wavelength nearly 0.1 nm
Solution:
(a) Gamma rays has lowest wavelength.
(b) Infrared radiations are used for taking photographs in dark.
(c) Gamma rays are produced by the changes in the nucleus of an atom.
(d) X-rays are of wavelength nearly 0.1nm.
Question: 17
Two waves A and B have wavelength of 0.01 A0and 9000 A0 respectively.
(a) Name the two waves.
(b) Compare the speeds of these waves when they travel in a vacuum.
Solution:
(a) Wave A is gamma ray and wave B is infrared ray.
(b) As both are electromagnetic radiation the speed is same. Hence, the ratio is 1;1.
Question: 18
Name two sources, each of infrared radiations and ultraviolet radiations.
Solution: Infrared lamp are source infrared radiations and sparks are source of ultraviolet radiations. Sun gives out all types of radiations.
Question: 19
What are infrared radiations? How are they detected? State one use of these radiations.
Solution: The radiation between 800 nm to 106nm. Thermopile is used to detect the infrared radiations. The galvanometer comes with thermopile shows deflection when infrared radiations fall on the thermopile. Infrared radiations are used for therapeutic purpose by doctors.
Question: 20
What are ultraviolet radiations? How are they detected? State one use of these radiations.
Solution: The radiation between 10 nm to 400 nm are called as ultraviolet radiations.
Ultraviolet radiations can be detected by their chemical activity on dyes and photographic plates. Ultraviolet rays are used in producing vitamin D in food of plants and animals.
Question: 21
Name three properties of ultraviolet radiations which are similar to visible light.
Solution: Ultraviolet radiations and visible have same speed, both the radiations affect the photographic plate but in different intensity and both the radiations follows the law of reflection and refraction.
Question: 22
Give two properties of ultraviolet radiations which differ from visible light.
Solution:
Ultraviolet radiations |
Visible light |
These can pass through quartz but absorbed by glass | These can pass through glass but absorbed by quartz. |
They are usually completely scattered in the atmosphere due to lower wavelength. | They are not completely scattered in the atmosphere. |
Question: 23
Mention three properties of infrared radiations similar to visible light.
Solution: Infrared radiations and visible have same speed, both the radiations unaffected by electric and magnetic field and both the radiations follows the law of reflection and refraction.
Question: 24
Give two properties of infrared radiations which differ from the visible light.
Solution:
infrared radiations |
Visible light |
These are not absorbed by rock salt but absorbed by glass | These can pass through glass but absorbed by rock salt. |
They produce heating effect that can be detected on a thermopile. | They can’t produce heating effect that can be detected on a thermopile. |
Question: 25
Name the material of prism required for obtaining the spectrum of (a) ultraviolet light, (b) infrared radiations
Solution:
(a) A quartz prism.
(b) A rock salt prism.
Question: 26
Name the radiations which are absorbed by the green house gases in the earth’s atmosphere.
Solution: Infrared radiation.
Question: 27
State one harmful effect each of the (a) ultraviolet and (b) infrared radiations.
Solution:
(a) ultraviolet rays can cause skin cancer if exposed for longer durations.
(b) Infrared radiations can cause skin burn.
Question: 28
Give reason for the following:
(i) Infrared radiations are used for photography in fog
(ii) Infrared radiations are used for signals during war.
(iii) The photographic darkrooms are provided with infrared lamps.
(iv) A rock salt prism is used instead of a glass prism to obtain the infrared spectrum.
(v) A quartz prism is required for obtaining the spectrum of ultraviolet light.
(vi) Ultraviolet bulbs have a quartz envelope instead of glass.
Solution:
(i) Due to their longer wavelength infrared radiation show low amount of scattering hence they are use for photography in fog.
(ii) Infrared radiations are invisible and don’t get easily absorbed in the medium. Hence, the are used for signals during war.
(iii) Photographic plates don’t react to infrared light. Hence, they used in dark rooms to create some visibility.
(iv) As infrared radiations are not absorbed by the rock salt. Rock salt prism is used to obtain infrared spectrum.
(v) As ultraviolet radiations are not absorbed by the quartz. A quartz prism is used to obtain ultraviolet spectrum.
(vi) As ultraviolet radiations are not absorbed by the quartz. A quartz envelope is used to in ultraviolet bulb.
Multiple Choice Type:
Question: 1
The most energetic electromagnetic radiations are:
(a) microwaves
(b) ultraviolet waves
(c) X- rays
(d) gamma rays
Solution: (d) gamma rays
Question: 2
The source of ultraviolet light is:
(a) electric bulb
(b) red hot iron ball
(c) sodium vapour lamp
(d) carbon arc-lamp
Solution: (d) carbon arc-lamp
Question: 3
A radiation P is focused by a proper device on the bulb of a thermometer. Mercury in the thermometer shows a rapid increase. The radiation P is:
(a) infrared radiation
(b) visible light
(c) ultraviolet radiation
(d) X-rays
Solution: (a) infrared radiation
Numerical
Question: 1
An electromagnetic wave has a frequency of 500MHz and a wavelength of 60cm.
(a) Calculate the speed of the wave.
(b) Name the medium through which it is travelling.
Solution: Given
Wavelength = 60cm = 0.6m
Frequency = 500 MHz = 5 x 108 Hz
Velocity of wave = wavelength x frequency
= 0.6 x 5 x 108
= 3 x 108 m/s
The wave is travelling to air.
Question: 2
The wavelength of X-rays is 0.01 A0. Calculate its frequency. State the assumption made, if any.
Solution: Given
Wavelength = 0.01 A0 = 0.01 x 10-10m
Velocity of x-ray = 3 x 108 m/s
Frequency = speed / wavelength
Frequency = 3 x 108 / 0.01 x 10-10
= 3 x 1020 Hz
Exercise 6 (c)
Question: 1
What is meant by scattering of light?
Solution: The process of absorption and then re-emission of light energy by the dust particles and air molecules present in the atmosphere is called as scattering of light.
Question: 2
How does the intensity of scattered light depend on the wavelength of incident light? State conditions when this dependence hold.
Solution: Intensity of scattered light is inversely proportional to the fourth power of the wavelength. It happens only when air molecules are smaller than the wavelength of light.
Question: 3
When sunlight enters the earth’s atmosphere, state which colour of light is scattered (i) the most, and (ii) the least.
Solution: Violet colour is scattered the most and red colour is scattered the least.
Question: 4
A beam of blue, green and yellow light passes through the Earth’s atmosphere. Name the colour which is scattered (a) the least (b) the most
Solution: yellow colour scatters the least and blue colour will scatters the most.
Question: 5
Which colour of white light is scattered the least? Give reason.
Solution: Red colour of white light is scattered the least. As the intensity of the scattering is inversely proportional the fourth power the wavelength the red light has the longest wavelength hence it gets scattered the least.
Question: 6
The danger signal is red. Why?
Solution: As the intensity of the scattering is inversely proportional the fourth power the wavelength the red light has the longest wavelength hence it gets scattered the least. Hence red colour scatters the least by air molecules hence it can penetrate for longer distance. Due to this red colour is more distinctly visible hence danger signal is red.
Question: 7
How would the sky appear when seen from the space (or moon)? Give reason for your ans.
Solution: scattering requires some sort of medium such as air. As the space is vaccum there is no scattering the space. Hence sky will appear black from the space.
Question: 8
What characteristic property of light is responsible for the blue colour of the sky?
Solution: Scattering property.
Question: 9
The colour sky, in direction other than of the sun, is blue. Explain.
Solution: as the light coming sun is a spectrum of light. As this light enters in the atmosphere blue colour gets scattered due to its shorter wavelength and red colour most prominently reaches our eye. Hence, colour of the sky in the direction of the sun is blue.
Question: 10
Why does the sun appear red at sunrise and sunset?
Solution: At sunrise and sunset the light travels maximum distance towards us. Hence when light reaches our eye most of the blue light is already scattered in the atmosphere. The red light which is of longer wavelength does not get scattered that much. Due to this the light that reaches to our eye is mostly made of red light that’s why sun appear red at sunrise and sunset.
Question: 11
The sky at noon appears white. Give reason.
Solution: At noon the light travels least distance to reach the observer. Hence, light gets less time to get scattered. Most of light stays un scattered. Due to this sky appears white at noon.
Question: 12
The clouds are seen as white. Explain.
Solution: Cloud contains droplet which are bigger than wavelength of all the colours of the light. Hence, these droplets scatter whole spectrum of light due to this cloud appear white.
Question: 13
Give reason why the smoke from a fire looks white.
Solution: Smoke contains particles which are bigger than wavelength of all the colours of the light. Hence, these particles scatter whole spectrum of light due to this smoke appear white.
Multiple Choice Type:
Question: 1
In the white light of the sun, maximum scattering by the air molecules present in the earth’s atmosphere is for:
(a) red colour
(b) yellow colour
(c) green colour
(d) blue colour
Solution: (d) blue colour
Question: 2
To an astronaut in a space-ship, the earth appears:
(a) white
(b) red
(c) blue
(d) black
Solution: (c) blue