Electromagnetic Radiation

Energy from the Sun

Most of the energy that is moving within Earth’s atmosphere and
across Earth’s surface comes from the sun. The sun’s energy
travels to Earth as electromagnetic radiation, a form of energy that
can move through the vacuum of space. Electromagnetic waves
consist of an electric field and a magnetic field.

When you use a microwave oven or watch television, you are
using the energy created by electromagnetic waves. The waves
are classified according to wavelength, or distance between wave
peaks. Most of the electromagnetic waves that travel from the sun
and reach Earth are in the form of visible light, which you can see
in Figure 1, and infrared radiation. A smaller amount arrives as
ultraviolet (UV) radiation

Sunlight and the Atmosphere

In order for the sun’s energy to reach Earth’s surface and sustain life, it
must first get through the atmosphere. Earth’s atmosphere is divided into
layers based on temperature. Some sunlight is absorbed or reflected by
the different levels of the atmosphere before it can reach the surface, as
shown in Figure 2.

Some UV wavelengths are absorbed by the topmost layer of the
atmosphere, called the thermosphere. More UV energy, along with some
infrared energy, is absorbed in the next layer, the mesosphere. Below
that, in the stratosphere, ozone absorbs more infrared and UV energy.
Without the ozone layer, too much UV radiation would reach Earth’s
surface and threaten the health of organisms. However, the amount of
UV radiation that reaches Earth’s surface can still be damaging, which is
why humans benefit from wearing clothing, sunscreen, and sunglasses.

By the time sunlight reaches the troposphere, there is some infrared
radiation, some UV radiation, and visible light. Some light has been
reflected into space by clouds. The daytime sky on a cloudless day
appears blue because gas molecules scatter short wavelengths of
visible light, which are blue and violet, more than the longer red and
orange wavelengths.

Multiple Choice

What percentage of the Sun's energy is reflected back into space?

• 100%

• About 50%

• About 30%

• It depends on the weather.

Multiple Choice

How are electromagnetic waves different from other waves?

• They have very short wavelengths

• They can travel through empty space

• They transmit energy instead of matter

• They can change direction by reflection

Multiple Choice

Is this statement True or False ?

The law of conservation of energy states that energy can neither be created nor destroyed - only converted from one form of energy to another.

• True

• False

EM Waves can travel in a vacuum! Mechanical waves (sound waves) CANNOT!!!

Multiple Choice

All waves carry...

• Energy

• Matter

• Light

• Particles

Multiple Choice

The heat from the sun on a summer day.

• Conduction

• Convection

• Radiation

Earth’s Energy Budget

Of the radiation that travels from the sun to the
troposphere, only about 50 percent is absorbed by land
and water and converted, or transformed, to heat. The rest,
as shown in Figure 3, is reflected by clouds and other
particles in the atmosphere (25%), absorbed by gases and
particles (20%), or reflected by the surface itself (5%).
Snow, ice, and liquid water reflect some sunlight back into
the atmosphere, where some will be absorbed by clouds
and particles that the energy missed on the way down.

Only a tiny fraction of the visible light that reaches Earth’s
surface is transformed to chemical energy in plants and
other photosynthetic organisms. The rest is absorbed by
Earth and re-emitted into the atmosphere as infrared
radiation. Earth’s surface absorbs and re-emits equal
amounts of energy so that its energy remains in balance
over time.

Open Ended

What questions do you have about this lesson?

Multiple Choice

If greenhouse gases increase and build up in our atmosphere, what happens?

• They trap more heat and global temperatures rise.

• They trap more heat and global temperatures decrease.

• They trap less heat and global temperatures rise.

• They trap less heat and global temperatures decrease.