** Question No : 1**

All radiations in a black body are

Reflected

Refracted

Transmitted

Absorbed

** Question No : 2**

According to Stefan Boltzmann law, the total radiation from a black body per second per unit area is directly proportional to the

Absolute temperature

Square of the absolute temperature

Cube of the absolute temperature

Fourth power of the absolute temperature

** Question No : 3**

The logarithmic mean temperature difference (t_{m}) is given by (where Δt_{1} and Δt_{2} are temperature differences between the hot and cold fluids at entrance and exit)

t_{m} = (Δt_{1} - Δt_{2})/ log_{e} (Δt_{1}/Δt_{2})

t_{m} = log_{e} (Δt_{1}/Δt_{2})/ (Δt_{1} - Δt_{2})

t_{m} = t_{m} = (Δt_{1} - Δt_{2}) log_{e} (Δt_{1}/Δt_{2})

t_{m} = log_{e} (Δt_{1} - Δt_{2})/ Δt_{1}/Δt_{2}

** Question No : 4**

According to Newton's law of cooling, the heat transfer from a hot body to a cold body is

Directly proportional to the surface area

Directly proportional to the difference of temperatures between the two bodies

Either (A) or (B)

Both (A) and (B)

** Question No : 5**

When absorptivity (α) = 1, reflectivity (ρ) = 0 and transmissivity (τ) = 0, then the body is said to be a

Black body

Grey body

Opaque body

White body

** Question No : 6**

In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by

Convection

Radiation

Conduction

Both convection and conduction

** Question No : 7**

The ratio of Nusselt number and the product of Reynold's number and Prandtl number is equal to

Stanton number

Biot number

Peclet number

Grashoff number