NCERT Solution Physics Class 12 Chapter 8 Electromagnetic Waves
NCERT Solution Physics Class 12 Chapter 8 Electromagnetic Waves all questions and answers. Physics Class 12 8th Chapter Electromagnetic Waves exercise solution and experts answer. As one of online learning platforms, we (netex.) are excited to offer the NCERT Solution Physics Class 12 Chapter 8. This solution is designed to help students who are looking to brush up on their physics concepts on Chapter 8 Electromagnetic Waves.
8.1)
8.7)
8.9) The terminology of different parts of the electromagnetic spectrum is given in the text. Use the formula E = hν (for energy of a quantum of radiation: photon) and obtain the photon energy in units of eV for different parts of the electromagnetic spectrum. In what way are the different scales of photon energies that you obtain related to the sources of electromagnetic radiation?
ANSWER-
8.10)
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8.11)
8.13.) Use the formula λm T = 0.29 cm K to obtain the characteristic temperature ranges for different parts of the electromagnetic spectrum. What do the numbers that you obtain tell you?
ANSWER-
Given formula is
λ m T = 0.29 cm K
For different parts of the electromagnetic spectrum we will get temperature ranges as
Hence number obtain tells us the temperature range required to get particular wavelength.
8.14. Given below are some famous numbers associated with electromagnetic radiations in different contexts in physics. State the part of the electromagnetic spectrum to which each belongs.
(a) 21 cm (wavelength emitted by atomic hydrogen in interstellar space).
(b) 1057 MHz (frequency of radiation arising from two close energy levels in hydrogen; known as Lamb shift).
(c) 2.7 K [temperature associated with the isotropic radiation filling all space-thought to be a relic of the ‘big-bang’ origin of the universe].
(d) 5890 Å – 5896 Å [double lines of sodium]
(e) 14.4 keV [energy of a particular transition in 57Fe nucleus associated with a famous high resolution spectroscopic method (Mossbauer spectroscopy)].
ANSWER-
(a) 21 cm (wavelength emitted by atomic hydrogen in interstellar space) as this is emitted by hydrogen hence it is at the end of the short wavelength range.
(b) 1057 MHz (frequency of radiation arising from two close energy levels in hydrogen; known as Lamb shift) it is radio wave from radio magnetic spectrum.
(c) temperature given as 2.7 K hence using maximum wavelength given by plancks law,
λm = 0.29/T = 0.29/2.7 = 0.11 cm
From electromagnetic spectrum this wavelength belongs to the microwave.
(d)5890 Å – 5896 Å. This wavelength related to visible region of spectrum particularly related to yellow light spectrum.
(e) Given energy = 14.4 KeV = 14.4 x 103 eV = 14.4 x 103 x 1.6 x 10-19
Transition energy is given by,
8.15 Answer the following questions:
(a) Long distance radio broadcasts use short-wave bands. Why?
(b) It is necessary to use satellites for long distance TV transmission. Why?
(c) Optical and radio telescopes are built on the ground but X-ray astronomy is possible only from satellites orbiting the earth. Why?
(d) The small ozone layer on top of the stratosphere is crucial for human survival. Why?
(e) If the earth did not have an atmosphere, would its average surface temperature be higher or lower than what it is now?
(f) Some scientists have predicted that a global nuclear war on the earth would be followed by a severe ‘nuclear winter’ with a devastating effect on life on earth. What might be the basis of this prediction?
ANSWER-
(a)for long distance radio broadcasting the method used is sky wave propagation in which signal is reflected back to the earth from the ionosphere and we know that ionosphere reflects the frequency in the range of 3 MHZ to 30 MHZ and this range is short range hence for Long distance radio broadcasts use short-wave bands.
(b) Signals of long distance TV transmission have large frequencies. So these signals are penetrated through ionosphere as ionosphere can reflect only short frequency wave bands. So for transmission of these high frequency signals satellites need to be used.
(c) X-ray astronomy is possible only from satellites orbiting the earth and not on the earth the major reason behind it lies in the property of X ray astronomy. As x ray cannot be penetrated through atmosphere hence it can’t be built on the ground. on the other hand optical or radio waves are not absorbed by atmosphere so they can penetrate the atmosphere hence telescopes for radio and optics can be built on ground in atmosphere.
(d)We know that ozone layer can absorb ultraviolet radiations coming from sunlight. These radiations if come to the earth surface will increase global warming and various skin related problems like skin cancer etc. hence by preventing these harmful radiations coming to earth ozone layer playing crucial role for human survival.
(e)In the absence of an atmosphere, the temperature of the Earth would decrease and make everything very chill like fridge. As major reason of heat trapped into the earth is the atmosphere which is not allowing the heat radiations to go out of the earth’s atmosphere thereby resulting in the greenhouse effect so in the absence of atmosphere there will be no greenhouse effect.
(f)after nuclear war because of nuclear bomb reactions there will be smoke everywhere which would cover the sky and won’t allow the sunlight to reach to the earth thereby reducing the temperature of earth by large extend and earth in lack of sunlight will experience the severe winter.
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