Stefan’s Law Practical Viva Questions and Answers 2023

A body that absorb all the incident radiation irrespective of frequency is  called a black body.

Black body is the one which absorbs all radiation which incident on it. On heating black body stats emitting radiations called black body radiation which are independent of nature of body and depends on the temperature of black body.

Due to the fact that whatever may be the colour of incident radiation the body appear black.

Radiating body in our experiment is tungsten filament.

The process by which that is transmitted directly from one body to another or from one place to another heating the intervening medium is called radiation.

Newton’s law of calling is applicable only when the difference of temperature between the body and the surroundings is very small. This law, infact, can be deduced from stefan’s law assuming the temperature difference as small.

Stefan’s constant is used to determine the temperature of the heavenly bodies like sun.

Resistance increases with increase of temperature.

It states that at any temperature, the ratio of emissive power of the absorptive power of a given wavelength is same for all bodies.

The wavelength corresponding to the maximum energy is inversely proportional to the absolute temperature.

Emissive power and absorptive power

Emissive power : At a particular temperature and for a given wave length it is defined as the radiant energy emitted per unit time per unit surface area of the body within a unit wavelength range.

Absorptive power : At a particular temperature and for a given wavelength, it is defined as the ratio of the radiant energy absorbed per second per unit surface area of the body to the total energy falling per unit time on the same area.

The emissivity of a perfectly black body is unity, whereas it is less than one for non-perfect black bodies.

When a metal is heated, the free electron in the metal gain kinetic energy sufficient to escape through the surface of metal. This process of electron emission is called thermionic emission.

The amount of energy radiated by a black body is not uniformaly distributed over all the wavelength emitted by the body but it is maximum for a particular wavelength. The value of wavelength is different for different temperature and varies with temperature.

Solar constant defined as the amount of energy received/sec/unit area of a perfect black surface at a mean distance of the earth from the sun in the absence of earth atmosphere, the surface being perpendicular to the direction of sun rays. [1.34 KW/m]

Black body radiations travel with velocity of light, straight line, obeys inverse square law, travel in vaccum, reflected diffracted polarized and without affecting the waves travel.

Sensation of hotness is called heat. Degree of hotness is called temperature.

Conduction, Convection and radiation

Conduction is mode of transmission of heat in which heat in which heat travels from the hot part of the body to its cold part without actual motion of heated particles.

Convection is the mode of transmission of heat from one part of the medium to the other by the bodily motion of heated particles.

Radiation is mode of transmission of heat which heat is transferred from one body to another without heating the intervening medium.