The sum of reflectivity and absorptivity for an opaque body is equal to

When α is absorptivity, ρ is reflectivity and τ is transmissivity, then for a diathermanous body,

A

α = 1, ρ = 0 and τ = 0

B

α = 0, ρ = 1 and τ = 0

C

α = 0, ρ = 0 and τ = 1

D

α + ρ = 1 and τ = 0

Absorptivity of a perfect black body is unity. Which of the following has maximum absorptivity?

A

Aluminium foil

B

Refractory bricks

C

Iron plate

D

Coke breeze

Absorptivity of a body will be equal to its emissivity

A

At all temperatures

B

At one particular temperature

C

When system is under thermal equilibrium

D

At critical temperature

The absorptivity of a body is equal to its emissivity

A

At a particular temperature

B

For circular bodies

C

Under thermal equilibrium

D

None of these

Depending on the radiating properties, a body will be opaque when

A

p = 0, x = 0 and a = 1

B

p = 1, x = 0 and a = 0

C

p = 0, x = 1 and a = 0

D

x = 0, a + p = 1

Absorptivity and refletivity of a perfect black body are respectively

A

1 and 0

B

0 and 1

C

1 and $$\infty $$

D

0 and 0.5

In thermal radiation for a black body (where, ε is emissivity and α is absorptivity)

A

α = 1; ε ≠ 1

B

α ≠ 1, ε = 1

C

α ≠ 1, ε ≠ 1

D

α = 1; ε = 1

A grey body is one whose absorptivity

A

Varies with temperature

B

Varies with wavelength of the incident ray

C

Is equal to its emissivity

D

Does not vary with temperature and. wavelength of the incident ray

The ratio of total radiating power to the absorptivity of the body depends upon the __________ as per Kirchoffs law.

A

Wavelength of radiation

B

Nature of the body

C

Temperature of the body

D

None of these

As per Kirchoffs law, the ratio of the total radiating power to the absorptivity of a body depends on the

A

Temperature of the body only

B

Wavelength of monochromatic radiation

C

Both A and B

D

Nature of material of body

The sum of reflectivity and absorptivity for an opaque body is equal to

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