ICSE-X-Physics
06: Spectrum of Light
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- Qstn #18What is the range of wavelength of the spectrum of white light in (i) Ã…, (ii) nm?Ans : 18 Seven prominent colours of the white light spectrum in order of their increasing frequencies: Red, Orange, Yellow, Green, Blue, Indigo, Violet
- Qstn #19Write the approximate wavelengths for (i) blue and (ii) red light.Ans : 19 Green, Yellow orange and red have wavelength longer than blue light.
Multiple Choice Type
- #Section : B
- Qstn #1When 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 dispersionAns : 1 Both deviation and dispersion.
Hint: When a white light ray falls on the first surface of a prism, light rays of different colours due to their different speeds in glass get refracted (or deviated) through different angles. Thus, the dispersion of white light into its constituent colours takes place at the first surface of prism.
- Qstn #2In 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) blueAns : 2 The colour of the extreme end opposite to the base of the prism is red.
Hint: The angle of deviation decreases with the increase in wavelength of light for a given angle of incidence. Since the red light has greatest wavelength, it gets deviated the least and is seen on the extreme end opposite to the base of prism.
Numericals
- #Section : C
- Qstn #1Calculate the frequency of yellow light of wavelength 550nm. The speed of light is 3 ×
108
m/s-1Ans : 1 Given, wavelength λ = 550 nm = 550
× 10-9 m
Speed of light, c = 3
× 108 m/s
We know that,
Frequency = Speed of light/wave length
Or, frequency = (3 × 108)/(550 × 10-9)
= 5.4
× 1014 HZ
- Qstn #2The frequency range of visible light is from 3.75
×
1014
Hz to 7.5
×
1014
Hz. Calculate its wavelength range. Take speed of light = 3
×
108
m/s-1Ans : 2 Speed of light, c = 3
×108m/s
Frequency range = 3.75
×1014 Hz to 7.5
× 1014 Hz.
Speed of light = frequency
× wavelength
For frequency = 3.75
× 1014 Hz
Λ = c/v = (3
× 108 m/s)/(3.75
×1014 Hz) = 8 × 10-7 m = 8000 Å
For frequency = 7.5 × 1014 Hz
Λ = c/v = (3 × 108 m/s)/(7.5
× 1014 Hz) = 4 × 10-7m = 4000 Å
Wavelength range = 4000 Ã… to 8000 Ã…
Exercise 6 B
- #Section : D
- #1Ans : 1
- #1-aGive a list of at least five radiations, in order of their increasing frequencies, which make up the complete electromagnetic spectrum.Ans : Five radiations, in the order of their increasing frequencies are:
Infrared waves, Visible light, Ultraviolet, X-rays and Gamma rays.
- #1-bWhich of the radiation mentioned in answer to part
(a) has the highest penetrating power?Ans : Gamma rays have the highest penetrating power.
- #2Ans : 2
- #2-aArrange the following radiations in the order of their increasing wavelength: X-rays, infrared rays, ratio waves, gamma ray and micro waves?Ans : Gamma rays, X-rays, infrared rays, micro waves, radio waves.
- #2-bWhich radiation is used for satellite communication?Ans : Microwave is used for satellite communication.