Theory:

We feel the sun's heat during the day while walking on a road or when we come out of a house.
 
How does the heat of the sun reach us? Is it through convection? No. Because there is no air in most of the space.
 
From the sun, the heat comes to us by another process known as radiation.
 
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Fig. - Example for radiation
 
The transfer of heat by radiation does not require any medium. It can take place whether a medium is present or not.
Example:
1. We can see the radiation in our kitchen. When a hot pan is kept away from the flame, the pan cools down as it transfers heat to the surroundings by radiation.
 
2. Visible light from a candle

3. X-rays from an x-ray machine
 
4. The heat from a stove burner
 
5. In a microwave machine, the foods are heated directly without any heating medium.
Important!
Remember that all hot objects radiate heat. When heat falls on an object, a part of the heat is reflected, a part  of the heat is absorbed, and a part is transmitted. But, the temperature of the object will increase only when the body absorbs the heat.