1
Which of the following is closest to an ideal black body?
- lamp black
- cavity maintained at constant temperature
- platinum black
- a lump of charcoal heated to high temperature.
Answer
(2) cavity maintained at constant temperature
Solution
An ideal black body absorbs all radiation falling on it.
Lamp black, platinum black and charcoal absorb most, but not all, of the radiation.
A cavity with a small opening, kept at constant temperature, traps radiation entering it by repeated reflections inside, so practically all of it is absorbed; it also emits cavity (black body) radiation.
A cavity maintained at constant temperature is the closest to an ideal black body.
Answer: (2)
AIPMT 2002