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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
To which part of the electromagnetic spectrum does a wave of frequency 5 × 1019 Hz belong?
To which part of the electromagnetic spectrum does a wave of frequency 5 × 1011 Hz belong?
A plane electromagnetic wave travels in the vacuum along the 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?
The terminology of different parts of the electromagnetic spectrum is given in the text. Use the formula E = hv (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?
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?
If the earth did not have an atmosphere, would its average surface temperature be higher or lower than what it is now?
Name the phenomenon which shows the quantum nature of electromagnetic radiation.
A wave has wavelength 50 Å.
- Name the wave.
- State its speed in vacuum.
- State its one use.
The wavelengths for the light of red and blue colours are roughly 7.8 × `10^7` m and 4.8 × `10^7` m respectively.
(a) Which colour has the greater speed in vacuum?
(b) Which colour has the greater speed in glass?
State the approximate range of wavelength associated with the ultraviolet rays.
Name two electromagnetic waves of frequency smaller than that of violet light. State one use of each.
Name the waves produced by the changes in the nucleus of an atom.
Which part of electromagnetic spectrum is used in radar systems?
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?
An X-ray beam can be deflected
Consider a photon of a continuous X-ray coming from a Coolidge tube. Its energy comes from
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.
Mark the correct options.
(a) An atom with a vacancy has smaller energy that a neutral atom.
(b) K X-ray is emitted when a hole makes a jump from the K shell to some other shell.
(c) The wavelength of K X-ray is smaller than the wavelength of L X-ray of the same material.
(d) The wavelength of Kα X-ray is smaller than the wavelength of Kβ X-ray of the same material.
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.
Iron emits Kα X-ray of energy 6.4 keV. Calculate the times taken by an iron Kα photon to cross through a distance of 3 km.
(Use Planck constant h = 4.14 × 10-15 eVs, speed of light c = 3 × 108 m/s.)
Find the cutoff wavelength for the continuous X-rays coming from an X-ray tube operating at 30 kV.
(Use Planck constant h = 4.14 × 10-15 eVs, speed of light c = 3 × 108 m/s.)
Find the maximum potential difference which may be applied across an X-ray tube with tungsten target without emitting any characteristic K or L X-ray. The energy levels of the tungsten atom with an electron knocked out are as follows.
| Cell containing vacancy | K | L | M |
| Energy in keV | 69.5 | 11.3 | 2.3 |
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.)
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.
(Use Planck constant h = 6.63 × 10-34 Js= 4.14 × 10-15 eVs, speed of light c = 3 × 108 m/s.)
The distance between the cathode (filament) and the target in an X-ray tube is 1.5 m. If the cutoff wavelength is 30 pm, find the electric field between the cathode and the target.
(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.)
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
X-rays
| Gamma rays | D | C | Visible light | B | A |
The above table shows different parts of the electromagnetic spectrum.
(a) Identify the parts of the spectrum marked as A, B, C and D.
(b) Which of the radiations A or B has the higher frequency?
(c) State two properties which are common to all parts of the electromagnetic spectrum.
(d) Name one source of each of the radiation of electromagnetic spectrum.
(e) Name one detector for each of the radiation.
(f) Name one use of each of the radiation.
Name the part of the electromagnetic spectrum which is:
Produced by bombarding a metal target with high electrons.
Gamma rays and radio waves travel with the same velocity in free space. Distinguish between them in terms of their origin and the main application.
State three properties of infrared radiations similar to that of visible light.
State three properties of ultra-violet radiation similar to visible light.
Give one use of electromagnetic radiation in Ultraviolet radiation.
Answer briefly.
Why light waves travel in a vacuum whereas sound waves cannot?
Answer briefly.
What are radio waves?
Answer briefly.
Name the most harmful radiation entering the Earth's atmosphere from outer space.
Solve the numerical problem.
Calculate the wavelength in nm of an X-ray wave of frequency 2.0 × 1018 Hz.
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 ______.
The frequency of x-rays, y-rays and ultraviolet rays are respectively a, b and c. Then:-
Ozone layer above the earth's atmosphere will
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 of wavelengths λ1, λ2 and λ3 are used in a radar system, in water purifiers and in remote switches of TV, respectively.
- Identify the electromagnetic waves.
- Write one source for each of them.
Which one of the following electromagnetic radiation has the least wavelength?
Choose the correct option related to wavelengths (λ) of different parts of the electromagnetic spectrum.
What is the speed of radio waves in vacuum?
