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प्रश्न
Give a reason for the following:
Long-distance radio broadcasts use short-wave bands. Why?
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उत्तर
Long distance radio broadcasts use shortwave bands because only these bands can be refracted by the ionosphere.
संबंधित प्रश्न
What role dose infra-red radiation play in physical therapy?
What physical quantity is the same for X-rays of wavelength 10−10 m, red light of wavelength 6800 Å and radiowaves of wavelength 500 m?
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?
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?
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 (Mössbauer spectroscopy)].
Optical and radio telescopes are built on the ground but X-ray astronomy is possible only from satellites orbiting the earth. Why?
What do you understand by the statement, "Electromagnetic waves transport momentum"?
State Moseley's law
(a) Give a list of at least five radiations, in order of their increasing frequencies, which make up the complete electromagnetic spectrum.
(b) Which of the radiation mentioned by you in part (a) has the highest penetrating power.
What is the range of the wavelength of the following electromagnetic waves?
(a) Ultraviolet
What is the range of the wavelength of the following electromagnetic waves?
(a) Visible.
State the approximate range of wavelength associated with the ultraviolet rays.
State the approximate range of wavelength associated with visible light.
Name the waves used for taking photographs in dark.
Name the waves produced by the changes in the nucleus of an atom.
Name the waves of wavelength nearly 0.1 nm.
Name two sources, each of infrared radiations and ultraviolet radiations.
Name three properties of ultraviolet radiations which are similar to visible light.
An electromagnetic wave has a frequency of 500 MHz and a wavelength of 60 cm Calculate the velocity of the wave.
X-ray and visible light travel at the same speed in vacuum. Do they travel at the same speed in glass?
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 wavelength of Kα X-ray of tungsten is 21.3 pm. It takes 11.3 keV to knock out an electron from the L shell of a tungsten atom. What should be the minimum accelerating voltage across an X-ray tube having tungsten target which allows production of Kα X-ray?
(Use Planck constant h = 6.63 × 10-34 Js= 4.14 × 10-15 eVs, speed of light c = 3 × 108 m/s.)
A certain element emits Kα X-ray of energy 3.69 keV. Use the data from the previous problem to identify the element.
(Use Planck constant h = 6.63 × 10-34 Js= 4.14 × 10-15 eVs, speed of light c = 3 × 108 m/s.)
The Kα and Kβ X-rays of molybdenum have wavelengths 0.71 A and 0.63 A respectively. Find the wavelength of Lα X-ray of molybdenum.
The electron beam in a colour TV is accelerated through 32 kV and then strikes the screen. What is the wavelength of the most energetic X-ray photon?
(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.)
A free atom of iron emits Kα X-rays of energy 6.4 keV. Calculate the recoil kinetic energy of the atom. Mass of an iron atom = 9.3 × 10−26 kg.
(Use Planck constant h = 6.63 × 10-34 Js= 4.14 × 10-15 eVs, speed of light c = 3 × 108 m/s.)
Identify the part of the electromagnetic spectrum used in (i) radar and (ii) eye surgery. Write their frequency range.
Name two sources of ultraviolet radiation.
Name two sources of infrared radiation.
Give one use of electromagnetic radiation in Microwaves.
Answer briefly.
Can we produce a pure electric or magnetic wave in space? Why?
Light of wavelength `3500A` is incident on two metals A and B whose work functions are 3.2 eV and 1.9 eV respectively. Which metal will emit photoelectrons?
An electron beam is accelerated by a potential difference V to hit a metallic target to produce X-rays. It produces continuous as well as characteristic X-rays. If λmin is the smallest possible wavelength of X-ray in the spectrum, the variation of log λmin with log V is correctly represented in:
The area to be covered for T.V telecast is doubled then the height of transmitting antenna (T.V tower) will have to be:-
The frequency of e. m waves which is best suited .to observed of radius 3 × 10–4 his of the order of
The electric field intensity produced by the radiations coming from 100 W bulb at a 3 m distance is E. The electric field intensity produced by the radiations coming from 50 W bulb at the same distance is ______.
Electromagnetic waves with wavelength
- λ1 is used in satellite communication.
- λ2 is used to kill germs in water purifies.
- λ3 is used to detect leakage of oil in underground pipelines.
- λ4 is used to improve visibility in runways during fog and mist conditions.
- Identify and name the part of electromagnetic spectrum to which these radiations belong.
- Arrange these wavelengths in ascending order of their magnitude.
- Write one more application of each.
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 ______.
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?
Below is an incomplete table showing the arrangement of electromagnetic spectrum in the increasing order of their wavelength. Complete the table:
| Gamma ray | X - ray | UV rays | Visible rays | Infrared | A | Radio waves |
- Identify the radiation A.
- Name the radiation used to detect fracture in bones.
- Name one property common to both A and Radio waves.
What is the speed of radio waves in vacuum?
What happens when an electron collides with a positron?
What is the wavelength range of electromagnetic radiation used in radio broadcast?
