Electromagnetic Spectrum And Its Broad Classification Flashcards
What is the visible spectrum?
The spectrum of white light which lies between the red and the violet regions
What is the invisible spectrum?
The part of spectrum beyond the red extreme and the violet extreme is called the invisible spectrum
Give the waves of wavelength longer than the red part of visible spectrum in increasing order of wavelength
Infrared radiations, microwaves, radio waves
Give the waves of wavelength shorter than the violet part of visible spectrum in decreasing order of wavelength
Ultraviolet rays, X rays and gamma rays
Give the complete electromagnetic spectrum in increasing order of wavelengths (or decreasing order of frequencies)
- Gamma rays
- X-rays
- Ultraviolet rays
- Visible light
- Infrared radiations
- Microwaves
- Radio waves
What is the infrared part of the spectrum?
The part of the spectrum just beyond the red end
What is the ultraviolet part of the spectrum?
The part of the spectrum just before the violet end
Give the properties common to all electromagnetic waves
- Electromagnetic waves do not require any material medium for their propagation
- They all travel w/ the same speed in vacuum and air
- They exhibit the properties of reflection and refraction
- These waves are not deflected by electric and magnetic fields
- These waves are transverse in nature
What changes and remains unchanged when an electromagnetic wave suffers refraction?
There is change in its direction, speed and wavelength, but its frequency remains unchanged
Give the wavelength of ultraviolet radiation
100 A to 4000 A
Give another name for ultraviolet radiations
Actinic rays
Which rays are chemically more active than visible light?
Ultraviolet rays - react with silver chloride soln. to turn it violet then finally dark brown
How can ultraviolet rays be detected?
By their chemical activity on dyes and photographic plates
How is the spectrum of ultraviolet radiations obtained?
By passing the radiations through a quartz prism because glass absorbs these radiations
Name the sources of ultraviolet radiations
- The electric arc and sparks
- A mercury vapour lamp
- Sun
A prism of which material is used to obtain the ultraviolet spectrum from its source?
A quartz prism instead of a glass prism
Why is a quartz prism used instead of a glass prism to obtain the ultraviolet spectrum from its source?
UR can pass through quartz but they are absorbed by glass
What is the material of the envelope of UR bulbs?
quartz
What is the speed of UR>
These radiation travel in a straight line w/ a speed of 3 * 10^8 m s-1 in air or vacuum
How are UR usually scattered?
By dust particles present in the earth’s atmosphere
Why do UR strongly affect a photographic plate?
They are chemically more active than visible light
On striking what do UR produce fluorescence?
On striking a zinc-sulphide screen
Which health hazards do UR cause if the human body is exposed to them for too long?
Skin cancer
State the uses of UR
- For sterilising air, surgical equipments, etc
- For detecting the purity of gems, eggs, ghee, etc
- In producing vitamin D in food of plants and animals
What is the wavelength range of IR?
8000 A to 10^7 A
How are infrared radiations detected?
When a thermometer is moved beyond the red extreme, a rapid rise in temperature is noticed. It means that the part of the spectrum beyond the red extreme of visible light, although not visible to us, has certain radiations which produce a strong heating effect
Give another name for IR
Heat radiations
Name the devices used to detect IR
- A thermometer
- A thermopile
- Rock-salt prism
How are IR detected using a thermopile?
The galvanometer connected with the thermopile shows deflection when IR fall on the thermopile
How are IR detected using a rock-salt prism?
A rock-slat prism does not absorb IR, whereas a glass prism absorbs them
