Explain why :

$(a)$ a body with large reflectivity is a poor emitter

$(b)$ a brass tumbler feels much colder than a wooden tray on a chilly day

$(c)$ an optical pyrometer (for measuring high temperatures) calibrated for an ideal black body radiation gives too low a value for the temperature of a red hot iron piece in the open, but gives a correct value for the temperature when the same piece is in the furnace

$(d)$ the earth without its atmosphere would be inhospitably cold

$(e)$ heating systems based on circulation of steam are more efficient in warming a building than those based on circulation of hot water

A body with a large reflectivity is a poor absorber of light radiations. A poor absorber will in turn be a poor emitter of radiations. Hence, a body with a large reflectivity is a poor emitter.

Brass is a good conductor of heat. When one touches a brass tumbler, heat is conducted from the body to the brass tumbler easily. Hence, the temperature of the body reduces to a lower value and one feels cooler.

Wood is a poor conductor of heat. When one touches a wooden tray, very little heat is conducted from the body to the wooden tray. Hence, there is only a negligible drop in the temperature of the body and one does not feel cool.

Thus, a brass tumbler feels colder than a wooden tray on a chilly day.

An optical pyrometer calibrated for an ideal black body radiation gives too low a value for temperature of a red hot iron piece kept in the open.

Black body radiation equation is given by

$E=\sigma\left(T^{4}-T_{0}^{4}\right)$

Where,

$E=$ Energy radiation

$T=$ Temperature of optical

pyrometer $T_{ o }=$ Temperature of open

space $\sigma=$ Constant

Hence, an increase in the temperature of open space reduces the radiation energy.

When the same piece of iron is placed in a furnace, the radiation energy, $E=\sigma T^{4}$

Without its atmosphere, earth would be inhospitably cold. In the absence of atmospheric gases, no extra heat will be trapped. All the heat would be radiated back from earth's surface.

A heating system based on the circulation of steam is more efficient in warming a building than that based on the circulation of hot water. This is because steam contains surplus heat in the form of latent heat $(540 \,cal / g )$