xenia-sti_taxi

Τετράδιο Εργασιών, σελ. 57 - 59

The main source of energy for our planet is the

Sun. A small part of the Sun's energy reaches

Earth. So far, you have learned about two ways in which

heat flows:

• Heat transfer by conduction

• Heat transfer by currents

xenia-sti_taxi

Τετράδιο Εργασιών, σελ. 57 - 59

Is it possible for energy to flow from the Sun to the Earth in any of the above ways?

• There is nothing between the Sun and the Earth, so heat transfer by conduction is not possible.

• Heat transfer by currents is not possible, since there is neither liquid nor gas between the Sun and the Earth.

xenia-sti_taxi

Τετράδιο Εργασιών, σελ. 57 - 59

Place your palm near the bottom of a lit lamp. What do you notice?

I notice that my hand is warming up.

xenia-sti_taxi

Τετράδιο Εργασιών, σελ. 57 - 59

• Heat transfer by conduction is not possible because air is a poor conductor of heat.

• Heat transfer by currents is not possible because hot air rises.

Is it possible for energy to flow from the Sun to the Earth in any of the above ways?

xenia-sti_taxi

Τετράδιο Εργασιών, σελ. 57 - 59

Place your book under a lamp or in sunlight for 5 minutes. Then touch your finger to the frame that is colored white and to the frame that is colored black. What do you notice?

The black frame is warmer than the white one.

xenia-sti_taxi

Τετράδιο Εργασιών, σελ. 57 - 59

Heat is spread by radiation. The heat absorbed by a body depends on its color.

xenia-sti_taxi

Τετράδιο Εργασιών, σελ. 57 - 59

Energy from the Sun to the Earth is transmitted by radiation, since the propagation of heat by radiation is possible in a vacuum.

How is energy spread from the Sun to Earth?

xenia-sti_taxi

Τετράδιο Εργασιών, σελ. 57 - 59

In the summer, dark-colored cars heat up more because dark-colored surfaces absorb more heat than light-colored ones.

Why do dark-colored cars heat up more than light-colored ones in the summer?

xenia-sti_taxi

Τετράδιο Εργασιών, σελ. 57 - 59

The lamp radiates heat in all directions. However, upward heat transfer also occurs through currents, since hot air rises.

If you put your hand on top of a light bulb, it gets hotter than if you put it next to or under the light bulb. Can you explain this observation?

Τέλος…