What is the value of Stefan-Boltzmann constant?

Σ = 5.670 × 10⁻⁸ W/(m²·K⁴)

True or False: A blackbody absorbs all incident radiation regardless of wavelength.

True. A blackbody is an ideal surface that absorbs 100% of incident radiation.

Wien's displacement law states λₘₐₓT = _____ μm·K

2897.8

Which property defines a gray surface?
A) Temperature-independent emissivity
B) Wavelength-independent emissivity
C) Direction-independent emissivity
D) Pressure-independent emissivity

B) Wavelength-independent emissivity

What happens to peak emission wavelength as temperature increases?

Peak emission wavelength shifts to shorter wavelengths (Wien's displacement law).

For large parallel plates, F₁₋₂ equals what value?

1

True or False: Kirchhoff's law (ε = α) applies regardless of temperature conditions.

False. It applies only when surface and radiation source are at same temperature.

What does radiosity (J) represent at a surface?

Total radiation leaving surface per unit area (emitted plus reflected radiation).

A small object in large enclosure has view factor F_small-large ≈ _____

1

Which surfaces emit maximum radiation at given temperature?
A) Gray surfaces
B) Diffuse surfaces
C) Real surfaces
D) Blackbody surfaces

D) Blackbody surfaces

What is emissivity range for real surfaces?

0 to 1

True or False: Convex surfaces have view factor to themselves greater than zero.

False. Flat or convex surfaces cannot 'see' themselves, so F_i-i = 0.

Energy balance at opaque surface requires α + ρ = _____

1

How do radiation shields reduce heat transfer?
A) Add conductive resistance
B) Add surface resistances
C) Block all radiation
D) Increase emissivity

B) Add surface resistances

What happens to radiation heat transfer when temperature doubles?

Increases by factor of 16 (due to T⁴ dependence in Stefan-Boltzmann law).

For concentric spheres, which area appears in radiation formula?

Inner sphere area (A₁)

True or False: Monatomic gases like nitrogen are transparent to thermal radiation.

True. Only polyatomic gases (CO₂, H₂O, CO) absorb thermal radiation significantly.

Radiation heat transfer coefficient h_r approximately equals 4εσT_m³ for _____ temperature differences.

Small

One radiation shield between parallel plates reduces heat transfer by approximately _____percent.

50

Which wavelength range contains most thermal radiation energy?
A) 0.01-1 μm
B) 0.1-100 μm
C) 1-1000 μm
D) 10-10000 μm

B) 0.1-100 μm

At what temperature do all surfaces stop emitting thermal radiation?

Absolute zero (0 K). All surfaces above absolute zero emit thermal radiation.