What happens when a wave runs into a barrier?
Reflection involves a change in direction of waves when they bounce off a barrier; refraction of waves involves a change in the direction of waves as they pass from one medium to another; and diffraction involves a change in direction of waves as they pass through an opening or around a barrier in their path.
What happens as the waves go around a barrier?
Diffraction: A wave encountering a small obstacle tends to bend around the obstacle. This bending of the wavefront is called diffraction. When a wave encounters a barrier with an aperture, which is much smaller than the wavelength, the wave bends and spreads out as a spherical circular wave.
What is a absorption?
Absorption is a condition in which something takes in another substance. The absorbent distributes the material it captures throughout whole and adsorbent only distributes it through the surface. The process of gas or liquid which penetrate into the body of adsorbent is commonly known as absorption.
What is absorptive power?
The absorptive power of a body is defined as the ratio of the energy absorbed for a given time to the energy incident on it for the same amount of time. It measures the amount of heat absorbed by an object. Since, a black body absorbs all the incident energy, its absorptive power is 1.
What is spectral absorptive power?
The spectral absorptive power of a body for a wave of wavelength X is defined as the ratio of the heat energy absorbed to the heat energy incident upon per unit time within the unit wavelength range (λ–1/2)to(λ+1/2) around X.
Is emissivity equal to absorptivity?
For all real objects, emissivity is also a function of wavelength. Note that when an object is in thermal equilibrium with its environment (steady state conditions, at the same temperature, no net heat transfer) the absorptivity is exactly equal to the emissivity (α=ε).
What is the absorptive power of black body?
The absorptive power of a body or a surface is defined as the ratio of the energy absorbed in a given time to the radiant energy incident on it at the same instant of time. The absorptive power of a black body is 1 because it absorbs radiant energy of all wavelengths incident on it.
Which of the following is the example of ideal black body?
A body is said to be a black body if it perfectly absorbs and radiates the energy but does not reflect it. A pin hole box is an ideal black body. Black board and kajal although black in colour need not to be black body.
What is black surface?
Black surfaces are good absorbers and radiators of heat. The colour of any object is the light it reflects. An object is white if it reflects all the light falling on it. An object is black if it reflects no or very little light and so absorbs almost all light.
What is mean by GREY body?
A gray body is an imperfect black body; i.e., a physical object that partially absorbs incident electromagnetic radiation. The ratio of a gray body’s thermal radiation to a black body’s thermal radiation at the same temperature is called the emissivity of the gray body.
What is black and GREY body?
black body is an object that absorbs all the radiant energy reaching its surface with all the wavelengths. WHILE A gray body is defined as a body whose absorption does not change with variation in temperature & wavelength of the incident radiation.
What is gray body emissivity?
A body with an emissivity less than unity and the same at all wavelengths is called a grey body, by comparison with a black body that has unit emissivity at all wavelengths. The emission from a grey body with ε = 0.80 is illustrated by the lower grey emission curve in the figure.
What is a gray body Mcq?
a body of which the monochromatic emissivity (ε) is constant for the entire wavelength spectrum.