Which of the following is the best definition of radiation?

a.
the movement of energy from one substance to another by direct contact

b.
the movement of a hot liquid of gas from one place to another, carrying energy with it

c.
the movement of energy in gas particles

d.
the movement of energy by waves that travel through space

D.  the movement of energy by waves that travel through space

Explanation:

There are three modes of heat transfer:

1. Conduction: This type of heat transfer happens when there is direct contact between the two object.

2.  Convection: his type of heat transfer happens when there is a movement of fluid (liquid or gas) in which convection currents are produced due to the movement of hot fluid upwards and cold fluid downwards. This happens as the density of hot fluid decreases and thus it moves upwards.

3. Radiation: This type of heat transfer happens when there is direct transfer of energy through space.

R = 6

Step-by-step explanation:

Remember... Circle area is:

A = pi×R^2

Where R is the circle radius.

Then,

Pi×R^2=36×Pi

R = square root of 36

R = 6