Physics [ 2 Marks Questions ]

When light is allowed to pass through a medium or an absorbing substance then the spectrum .obtained is known as absorption spectrum. It is the characteristic of absorbing substances.
The absorption spectrum is classified into three types:

1. Continuous absorption spectrum.
2. Line absorption spectrum.
3. Band absorption spectrum.

When the spectrum of the self-luminous sources is taken, we get the emission spectrum. Each source has its own characteristic emission spectrum. The emission spectrum can be divided into
three types:

1. Continuous emission spectra.
2. Line emission spectrum (or line spectrum).
3. Band emission spectrum (or band spectrum).

X-rays are used extensively in studying structures of inner atomic electron shells and crystal structures. It is used in detecting fractures, diseased organs, formation of bones and stones, observing the progress of healing bones. Further, in a finished metal product, it is used to detect faults, cracks, flaws, and holes.

It is used to destroy bacteria, sterilizing surgical instruments, burglar alarms, detect invisible writing, finger prints and also in the study of molecular structure.

It is used to produce dehydrated fruits; in green houses to keep the plants warm, heat therapy for muscular pain or sprain, TV remote as a signal carrier, to look through haze fog or mist and used in night vision or infrared photography.

It is used in radar systems for aircraft navigation, speed of the vehicle, microwave oven for cooking and very long-distance wireless communication through satellites.

It is used in radio and television communication systems and also in cellular phones to transmit voice communication in the ultra-high frequency band.

Microwaves have wavelength of the order of a few millimetres. Due to their short wavelengths, these are not diffracted (bent) much by objects of normal dimensions. So they can be transmitted as a beam in a particular direction.

The greenhouse effect is the phenomenon which keeps the earth’s surface warm at night. The earth reflects back infrared part of solar radiation. Infra-red rays are reflected back by low lying clouds and lower atmosphere and keep the earth’s surface warm at night.

Microwaves are produced due to oscillating currents in special vacuum tubes like Klystroms.

X-rays are produced due to the sudden deceleration of fast-moving electrons by a metal target.

Radiowaves are produced due to the accelerated motion of electrons in conducting wires or oscillating circuits.

When an object bums, it emits colours. That is, it emits electromagnetic radiation which depends on temperature. If the object becomes hot then it glows in red colour. If the temperature of the object is further increased then it glows in reddish-orange colour and becomes white when it is hottest. The spectrum usually called as black body spectrum.

The definite pattern of colours obtained on the screen after dispersion is called a spectrum.

The orderly distribution of electromagnetic radiations of all types according to their wavelength or frequency into distinct groups having widely differing properties is called the electromagnetic spectrum.

An electric dipole is a basic source of electromagnetic waves.

In EM waves, electric and magnetic fields oscillate in mutually perpendicular directions. These waves are transverse in nature.

Conduction Current:

1. It is due to the flow of electrons in a circuit.
2. It exists even if electrons flow at a uniform rate.

Displacement Current:

1. It is due to the time-varying electric field.
2. It does not exist under steady conditions.

James Clerk Maxwell was first predicted the existence of EM waves.