Question

give reasons

The back of refrigerators are coloured dull black.

Answer 1

so that the light does not pass through it. it works as a opaque median who absorb light

Answer 2

The back of the refrigerators have external coils .These coils radiate heat.

As per Kirchhoff’s radiation law, Those objects that are good absorbers, are also termed as good emitters.  Black is generally considered as a good heat absorbed.

So the heat radiated by the external coils would absorbed by the blackened surface of the refrigerator. As per Kirchhoff’s radiation law, we can conclude that black color would also be a good emitter.

Hence the blackened surface releases the heat away from the fridge so that the fridge would continue working well by remaining cool.