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Stars and galaxies emit different types of waves.
Stars and galaxies emit different types of waves.
Radio waves and visible light can pass through the Earth’s atmosphere and reach the ground without getting absorbed significantly.
Radio waves and visible light can pass through the Earth’s atmosphere and reach the ground without getting absorbed significantly.
Thus the radio telescopes and optical telescopes can be placed on the ground.
Thus the radio telescopes and optical telescopes can be placed on the ground.
All other type of waves get absorbed by the atmospheric gases and dust particles.
All other type of waves get absorbed by the atmospheric gases and dust particles.
Hence, the -ray, X-ray, ultraviolet, infrared, and microwave telescopes are kept aboard artificial satellites and are operated remotely from the Earth.
Hence, the -ray, X-ray, ultraviolet, infrared, and microwave telescopes are kept aboard artificial satellites and are operated remotely from the Earth.
Even though the visible radiation reaches the surface of the Earth, its intensity decreases to some extent due to absorption and scattering by atmospheric gases and dust particles.
Even though the visible radiation reaches the surface of the Earth, its intensity decreases to some extent due to absorption and scattering by atmospheric gases and dust particles.
Optical telescopes are therefore located at higher altitudes.
Optical telescopes are therefore located at higher altitudes.
The Indian Giant Metrewave Radio Telescope (GMRT) near Pune is an important milestone in the field of Radio-astronomy.
The Indian Giant Metrewave Radio Telescope (GMRT) near Pune is an important milestone in the field of Radio-astronomy.
Also, Indian Astronomical Observatory houses the Himalayan Chandra Telescope (HCT), the 2 m optical-IR Telescope, which is situated at Hanle, Ladakh, at an altitude of 4500 m.
Also, Indian Astronomical Observatory houses the Himalayan Chandra Telescope (HCT), the 2 m optical-IR Telescope, which is situated at Hanle, Ladakh, at an altitude of 4500 m.
1. A fluorescent light bulb is coated from with a powder inside and contains a gas; electricity causes the gas to emit ultraviolet radiation, which then stimulates the tube coating to emit light.
1. A fluorescent light bulb is coated from with a powder inside and contains a gas; electricity causes the gas to emit ultraviolet radiation, which then stimulates the tube coating to emit light.
2. The pixels of a television or computer screen fluoresce when electrons from an electron gun strike them.
2. The pixels of a television or computer screen fluoresce when electrons from an electron gun strike them.
3. What we call 'visible light' is just the part of the EM spectrum that human eyes see.
3. What we call 'visible light' is just the part of the EM spectrum that human eyes see.
Many other animals would define 'visible' somewhat differently.
Many other animals would define 'visible' somewhat differently.
For instance, many animals including insects and birds, see in the UV region.
For instance, many animals including insects and birds, see in the UV region.
Natural world is full of signals that animals see and humans cannot.
Natural world is full of signals that animals see and humans cannot.
Many birds including bluebirds, budgies, parrots and even peacocks have ultraviolet patterns that make them even more vivid to each other than they are to us.
Many birds including bluebirds, budgies, parrots and even peacocks have ultraviolet patterns that make them even more vivid to each other than they are to us.
Ionizing radiations :
Ionizing radiations :
Ultraviolet, X-ray and gamma rays have sufficient energy to cause ionization i.e. they strip electrons from atoms and molecules lying along their path.
Ultraviolet, X-ray and gamma rays have sufficient energy to cause ionization i.e. they strip electrons from atoms and molecules lying along their path.
The atoms lose their electrons and are then known as ions.
The atoms lose their electrons and are then known as ions.
Ionization is harmful to human beings because it can kill or damage living cells, or make them grow abnormally as cancers.
Ionization is harmful to human beings because it can kill or damage living cells, or make them grow abnormally as cancers.
Fluorescent lamps are based on ionization of gas. Ionizing radiation is also used in various equipments in laboratory and industry
Fluorescent lamps are based on ionization of gas. Ionizing radiation is also used in various equipments in laboratory and industry
X-rays have many practical applications in medicine and industry.
X-rays have many practical applications in medicine and industry.
Because X-ray photons are of such high energy, they can penetrate several centimetres of solid matter and can be used to visualize the interiors of materials that are opaque to ordinary light
Because X-ray photons are of such high energy, they can penetrate several centimetres of solid matter and can be used to visualize the interiors of materials that are opaque to ordinary light
To transmit a signal we need an antenna or an aerial.
To transmit a signal we need an antenna or an aerial.
For efficient transmission and reception, the transmitting and receiving antennas must have a length at least /4 where is the wavelength of the signal.
For efficient transmission and reception, the transmitting and receiving antennas must have a length at least /4 where is the wavelength of the signal.
The highest TV tower in Rameshwaram, Tamilnadu, is the tallest tower in India and is ranked 32nd in the world with pinnacle height of 323 metre.
The highest TV tower in Rameshwaram, Tamilnadu, is the tallest tower in India and is ranked 32nd in the world with pinnacle height of 323 metre.
It is used for television broadcast by the Doordarshan.
It is used for television broadcast by the Doordarshan.
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