EM waves Flashcards
What is Displacement Current?
The current due to changing electric field or electric flux is called called
displacement current.
.…………………………. is the source of electromagnetic waves.
An oscillating charge (accelerating charge)
List the properties of electromagnetic waves (any four)
▪ In an e.m waves are transverse waves in which the electric and
magnetic fields are perpendicular to each other, and also to
the direction of propagation.
▪ No material medium is required for the propagation of e.m.wave.
▪ Electromagnetic waves carry energy as they travel through space
and this energy is shared equally by the electric and magnetic fields.
▪ Electromagnetic waves transport momentum as well. When these
waves strike a surface, total momentum delivered to this surface is,
p = 𝑈/𝑐
where U is the energy
The electric and the magnetic fields in an electromagnetic wave
are related as E0/B0= c
Arrange electromagnetic waves in the increasing order of wavelength(or
decreasing order of frequency.
Gamma rays . X-rays , Ultraviolet rays, Visible rays, Infrared waves ,
Microwaves, Radio waves
How radio waves are produced ?
Radio waves are produced by the accelerated motion of charges in
conducting wires
Write the uses of radio waves.
▪ They are used in radio and television communication systems.
▪ Cellular phones use radio waves.
.How microwaves are produced?
▪ Microwaves are produced by special vacuum tubes called, klystrons,
magnetrons and Gunn diodes.
12.Write the uses of microwaves.
▪ Used for radar systems used in aircraft navigation .
▪ Used in speed guns used to time fast balls, tennis serves, and
automobiles.
▪ Microwaves are used in microwave ovens , for cooking.
How is food cooked in microwave ovens?
In microwave ovens, the frequency of the microwaves is selected to match
the resonant frequency of water molecules so that energy from the waves is
transferred efficiently to the kinetic energy of the molecules. This raises the
temperature of any food containing water
How infrared waves are produced?
Infrared waves are produced by hot bodies and molecules.
Write the uses of infrared waves.
▪ Infrared lamps are used in physical therapy.
▪ Infrared radiation plays an important role in maintaining the earth’s
warmth or average temperature through the greenhouse effect.
▪ Infrared detectors are used in Earth satellites, both for military
purposes and to observe growth of crops.
▪ LEDs emit infrared waves, which are used in the remote switches of
TV sets, video recorders and hi-fi systems.
Why IR waves are called heat waves?
Infrared waves are sometimes referred to as heat waves. This is because
water molecules present in most materials readily absorb infrared waves
After absorption, their thermal motion increases, that is, they heat up and
heat their surroundings.
Explain Greenhouse Effect.
Incoming visible light is absorbed by the earth’s surface and reradiated as
infrared (longer wavelength) radiations. This radiation is trapped by
greenhouse gases such as carbon dioxide and water vapour. This trapped
Infrared radiation maintains the earth’s warmth
How ultraviolet rays are produced?
Ultraviolet (UV) radiation is produced by special lamps and very hot
bodies. The sun is an important source of ultraviolet light.
Write the uses of UV rays.
▪ UV radiations are used in LASIK (Laser assisted in situ
keratomileusis) eye surgery.
▪ UV lamps are used to kill germs in water purifiers.
