Optical and Radio Telescopes Are Built on the Ground but X-ray Astronomy is Possible Only from Satellites Orbiting the Earth. Why? - Physics

Short Note

Optical and radio telescopes are built on the ground but X-ray astronomy is possible only from satellites orbiting the earth. Why?



With reference to X-ray astronomy, X-rays are absorbed by the atmosphere. However, visible and radio waves can penetrate it. Hence, optical and radio telescopes are built on the ground, while X-ray astronomy is possible only with the help of satellites orbiting the Earth.

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Chapter 8: Electromagnetic Waves - Exercise [Page 287]


NCERT Physics Class 12
Chapter 8 Electromagnetic Waves
Exercise | Q 8.15 (c) | Page 287
NCERT Physics Class 12
Chapter 8 Electromagnetic Waves
Exercise | Q 15.3 | Page 287

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Why are microwaves considered suitable for radar systems used in aircraft navigation?

Identify the part of the electromagnetic spectrum which is suitable for radar system used in aircraft navigation.

A plane electromagnetic wave travels in vacuum along z-direction. What can you say about the directions of its electric and magnetic field vectors? If the frequency of the wave is 30 MHz, what is its wavelength?

Give a reason for the following:

It is necessary to use satellites for long-distance TV transmission. Why?

State Moseley's law

What is the range of the wavelength of the following electromagnetic waves?
(a) Gamma rays.

State the approximate range of wavelength associated with  the ultraviolet rays .

State the approximate range of wavelength associated with infrared rays.

What are ultraviolet radiations? How are they detected? State one use of these radiations.

The source of ultraviolet light is :

X-ray and visible light travel at the same speed in vacuum. Do they travel at the same speed in glass?

Why is exposure to X-rays injurious to health but not exposure to visible light, when both are electromagnetic waves?

If the potential difference applied to the tube is doubled and the separation between the filament and the target is also doubled, the cutoff wavelength

Moseley's Law for characteristic X-ray is √v = a(Z − b). Here,

Frequencies of Kα X-rays of different materials are measured. Which one of the graphs in the figure may represent the relation between the frequency v and the atomic number ?

50% of the X-ray coming from a Coolidge tube is able to pass through a 0.1 mm thick aluminium foil. The potential difference between the target and the filament is increased. The thickness of the aluminium foil that will allow 50% of the X-ray to pass through will be

For harder X-rays,
(a) the wavelength is higher
(b) the intensity is higher
(c) the frequency is higher
(d) the photon energy is higher.

The potential difference applied to an X-ray tube is increased. As a result, in the emitted radiation,
(a) the intensity increases
(b) the minimum wavelength increases
(c) the intensity remains unchanged
(d) the minimum wavelength decreases.

X-ray incident on a material
(a) exerts a force on it
(b) transfers energy to it
(c) transfers momentum to it
(d) transfers impulse to it.

The Kα X-rays of aluminium (Z = 13) and zinc (Z = 30) have wavelengths 887 pm and 146 pm respectively. Use Moseley's  law √v = a(− b) to find the wavelengths of the Kα X-ray of iron (Z = 26).

(Use Planck constant h = 6.63 × 10-34 Js= 4.14 × 10-15 eVs, speed of light c = 3 × 108 m/s.)

The energy of a silver atom with a vacancy in K shell is 25.31 keV, in L shell is 3.56 keV and in M shell is 0.530 keV higher than the energy of the atom with no vacancy. Find the frequency of Kα, Kβ and Lα X-rays of silver.

(Use Planck constant h = 6.63 × 10-34 Js= 4.14 × 10-15 eVs, speed of light c = 3 × 108 m/s.)

If the operating potential in an X-ray tube is increased by 1%, by what percentage does the cutoff wavelength decrease?

(Use Planck constant h = 6.63 × 10-34 Js= 4.14 × 10-15 eVs, speed of light c = 3 × 108 m/s.)

The short-wavelength limit shifts by 26 pm when the operating voltage in an X-ray tube is increased to 1.5 times the original value. What was the original value of the operating voltage?

(Use Planck constant h = 6.63 × 10-34 Js= 4.14 × 10-15 eVs, speed of light c = 3 × 108 m/s.)

An X-ray tube operates at 40 kV. Suppose the electron converts 70% of its energy into a photon at each collision. Find the lowest there wavelengths emitted from the tube. Neglect the energy imparted to the atom with which the electron collides.

(Use Planck constant h = 6.63 × 10-34 Js= 4.14 × 10-15 eVs, speed of light c = 3 × 108 m/s.)

Suppose a monochromatic X-ray beam of wavelength 100 pm is sent through a Young's double slit and the interference pattern is observed on a photographic plate placed 40 cm away from the slit. What should be the separation between the slits so that the successive maxima on the screen are separated by a distance of 0.1 mm?

Continuous X-rays are made to strike a tissue paper soaked with polluted water. The incoming X-rays excite the atoms of the sample by knocking out the electrons from the inner shells. Characteristic X-rays are analysed and the intensity is plotted against the wavelength. Assuming that only Kα intensities are detected, list the elements present in the sample from the plot. Use Moseley's equation v − (25 × 1014Hz)(Z − 1)2.

(Use Planck constant h = 6.63 × 10-34 Js= 4.14 × 10-15 eVs, speed of light c = 3 × 108 m/s.)

Name the scientist who discovered Microwaves 

Name the scientist who discovered radio waves

State the name and the range of wavelength of the invisible electromagnetic waves beyond the red end of the visible spectrum.

Name three radiations and their wavelength range which are invisible and beyond the violet end of the visible spectrum.

Name the radiation which can be detected by thermopile.

To which regions of the electromagnetic spectrum do the following wavelengths belong: 
(a) 250 nm 
(b) 1500 nm 

Arrange the following electromagnetic waves in increasing order of their frequencies (i.e. begin with the lowest frequency):
Visible light, y rays, X rays, microwaves, radio waves, infrared radiations, and ultraviolet radiation.

Name the part of the electromagnetic spectrum which is: 
Suitable for radar systems used in aircraft navigation.

Name the part of the electromagnetic spectrum which is: 
Produced by bombarding a metal target with high electrons.

Calculate the shortest wavelength of electromagnetic radiation present in Balmer series of hydrogen spectrum.

State two uses of infrared radiations.

Choose the correct option.

The EM wave emitted by the Sun and responsible for heating the Earth’s atmosphere due to greenhouse effect is

Choose the correct option.

Earth’s atmosphere is richest in

Choose the correct option.

How does the frequency of a beam of ultraviolet light change when it travels from air into glass?

Answer briefly.

Why are microwaves used in radar?

Answer briefly.

Can we produce a pure electric or magnetic wave in space? Why?

Answer briefly.

Why light waves travel in a vacuum whereas sound waves cannot?

Answer briefly.

What are the ultraviolet rays?

Answer briefly.

What are radio waves?

Answer briefly.

Give two uses of radio waves.

Answer briefly.

Name the most harmful radiation entering the Earth's atmosphere from outer space.

Answer briefly.

What is a carrier wave?

Answer briefly.

Why high-frequency carrier waves are used for the transmission of audio signals?

Solve the numerical problem.

Calculate the frequency in MHz of a radio wave of wavelength 250 m. Remember that the speed of all EM waves in a vacuum is 3.0 × 108 m/s.

Solve the numerical problem.

Calculate the wavelength in nm of an X-ray wave of frequency 2.0 × 1018 Hz.

Calculate the wavelength of a microwave of a frequency of 8.0 GHz.

If the Earth did not have atmosphere, would its average surface temperature be higher or lower than what it is now? Explain.

X-rays, gamma rays and microwaves travelling in a vacuum have ______.

A bat moving at 10 ms−1 towards a wall sends a sound signal of 8000 Hz towards it. On reflection, it hears a sound of frequency f The value of f in Hz is close to (speed of sound = 320 ms−1)

Which of the following is a tool used for separating the different color wavelengths from each other?

A car is moving towards a high cliff. The car driver sounds a horn of frequency f. The reflected sound heard by the driver has a frequency 2f. If v be the velocity of sound, then the velocity of the car, in the same velocity units, will be:

For television broadcasting, the frequency employed is normally

Microwaves are electromagnetic waves with frequency in the range of.

The frequency of e. m waves which is best suited .to observed of radius 3 × 10–4 his of the order of

Find the photon energy in units of ev for electromagnetic wave if waves length 40 m. Given h = 6.63 × 10–34 J.

What is time period of the light for which the eye is most sensitive?

Radio waves of constant amplitude can be generated with.

SONAR emits which of the following waves?

If λv, λx and λm Am represents the wavelength of visible light, x-ray and microwaves respectively, then ______.

All components of the electromagnetic spectrum in a vacuum have the same ______

The half-value thickness of an absorber is defined as the thickness that will reduce exponentially the intensity of a beam of particles by a factor of 2. The half-value thickness in (µm) for lead assuming X-ray beam of wavelength 20 pm, µ = 50 cm-1 for X-rays in lead at wavelength λ = 20 pm, is ______ µm.

In uranium (Z = 92) the K absorption edge is 0.107 Å and the Kα line is 0.126 Å, and the wavelength of the L absorption edge is ______.

Given below in the left column are different modes of communication using the kinds of waves given in the right column. 

A.  Optical Fibre
P. Ultrasound
B. Radar Q. Infrared Light
C. Sonar R. Microwaves
D. Mobile Phones  S. Radio Waves

From the options given below, find the most appropriate match between entries in the left and the right column.

Which is the correct ascending order of wavelengths?

Photons of an electromagnetic radiation has an energy 11 keV each. To which region of electromagnetic spectrum does it belong? 

Which one of the following electromagnetic radiation has the least wavelength?

Assertion (A): Ultraviolet radiations is scattered more as compared to the microwave radiations.

Reason (R): Wavelength of ultraviolet radiation is more than the wavelength of microwave radiation.


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