Radiation

Question 1

Suns radiation is mostly at _____ wavelengths.

Answer 1

short, 0-4 μm

Question 2

In the case of solids and liquids radiation is a _____ phenomenon.

Answer 2

surface

Question 3

The equality of emissivity and absorptivity is postulated by _____ law.

Answer 3

Kirchhoff

Question 4

For an opaque surface high reflectivity means _____ emissivity.

Answer 4

low

Question 5

The total radiant energy incident on a surface is known as _____.

Answer 5

Irradiation

Question 6

Shape factor is _____ of surface properties.

Answer 6

independent

Question 7

Shape factor will _____ when surfaces are moved closer.

Answer 7

increase

Question 8

The radiant energy per unit solid angle in a direction is known as _____ of radiation.

Answer 8

intensity

Question 9

The wave length range for visual radiation is _____.

Answer 9

0.3 to 0.7 μm

Question 10

Solar collector surfaces should have low emissivity at _____ temperatures.

Answer 10

low

Question 11

Radiation from a small opening from an isothermal enclosure can be considered as _____.

Answer 11

black

Question 12

The wave length range of thermal radiation is _____.

Answer 12

1 to 100 μm

Question 13

Solar collector surfaces should have high absorptivity for _____ wavelength radiation

Answer 13

short

Question 14

CO2 and water vapor are _____ radiators.

Answer 14

band

Question 15

In the case of gases radiation is a _____ phenomenon.

Answer 15

volume

Question 16

Glasses generally transmit _____ wavelength radiation.

Answer 16

short

Question 17

Reciprocity theorem for shape factor is A1F1-2= _____.

Answer 17

A2F2-1

Question 18

The emissivity is constant in the case of a _____ surface.

Answer 18

gray

Question 19

Reradiating enclosure _____ the effective shape factor.

Answer 19

improves

Question 20

Radiation shield should have _____ reflectivity.

Answer 20

high

Question 21

Most of the real surfaces have emissivity _____ with angle from normal.

Answer 21

varying

Question 22

At any temperature as wavelength increases the monochromatic emissive power _____.

Answer 22

increases and then decreases

Question 23

For selective surface the emissivity is dependent on _____ of radiation.

Answer 23

temperature and wavelength

Question 24

The ratio of emissive power of a body to the emissive power of a black body is defined as _____.

Answer 24

emissivity

Question 25

The fraction of radiation emanating from surface 1 incident on surface 2 is called _____.

Answer 25

shape factor F1-2

Question 26

Diatomic gases are _____ for radiation.

Answer 26

Transparent

Question 27

F/T: Emissivity of a gas body depends on the partial pressure, thickness and temperature.

Answer 27

True

Question 28

F/T: As temperature difference increases, radiation resistance will increase.

Answer 28

False

Question 29

F/T: Gases are band radiators.

Answer 29

True

Question 30

F/T: Radiation from a gas body is a volume phenomenon.

Answer 30

True

Question 31

F/T: Opaque Gray surfaces have constant reflectivity.

Answer 31

True

Question 32

F/T: Glasses generally transmit low frequency radiation.

Answer 32

False

Question 33

F/T: Between two surfaces if F1–2 > F2–1 then A1 > A2.

Answer 33

False

Question 34

F/T: Snow is a very good reflector at all the wavelengths.

Answer 34

False

Question 35

F/T: Copper dioxide coating can produce selective surface.

Answer 35

True

Question 36

F/T: Shape factor with enclosing surfaces will be one.

Answer 36

True

Question 37

F/T: Gases are truly gray radiators.

Answer 37

False

Question 38

F/T: As temperature increases, the wavelength at which maximum monochromatic emissive power occurs increases.

Answer 38

False

Question 39

F/T: Convex surfaces will have shape factor with themselves.

Answer 39

False

Question 40

F/T: As temperature increases, hr will increase.

Answer 40

True

Question 41

F/T: Directional emissivity for metals will be lowest at the normal direction.

Answer 41

False