Today's Driving Question – How does solar energy reach the Earth? The Sun is 93 million miles away. A tiny fraction of the Sun’s energy hits the Earth (~a hundredth of a millionth of a percent) is enough to meet all our power needs many times over. In fact, every minute, enough energy arrives at the Earth to meet our whole demands for a year. We call the energy from the sun, solar energy. Just the tiny fraction of the Sun’s energy that hits the Earth. Solar energy is transmitted to the earth in the form of radiant energy. It is vital to us because it provides the world—directly or indirectly– with almost all of its energy. In addition to providing the energy that sustains the world, solar energy is stored in fossil fuels and biomass, and is responsible for powering the water cycle and producing wind. Today's Driving Question – How does solar energy reach the Earth?

Vocabulary Nuclear Reaction Fusion Fission Solar Energy Electromagnetic Spectrum Wavelength Frequency

What you should understand by the end of today’s lesson. How the suns energy is created How sun light travels The properties of light What happens to the solar energy that reaches the Earth

Nuclear Energy 100 megatron vs 1 trillion megatron

Nuclear Fission Neutron induced in U235 Fission is Exothermic The sum of the masses of the resulting nuclei is less than the original mass (about 0.1% less) The “missing mass” is converted to energy according to E=mc2

Sun Light L

Every second, the sun converts 500 million metric tons of hydrogen to helium. Due to the process of fusion, 5 million metric tons of excess material is converted into energy in each second. This means that every year, 157,680,000,000,000 metric tons are converted into energy.

Fusion Changes Mass to Energy E=mc2 .993 kg Helium He H 1kg Hydrogen

Cookie Fusion Procedure Cut 2 squares of wax paper 10 cm on a side Cut 5 cm wide slice of cookie dough (atom) Find the mass of the atom and record on the table Place the atom one cm away from the edge of a wax paper square Repeat step 2 thru 4 for a second atom Place the atoms about 2 cm from each other Place both atoms on a plate and microwave for 1 minute Remove the “new element” and let cool for 2 minutes Find the mass of the “new element” Complete the table

Cookie Fusion Mass Before Cooking Mass After Cooking Atom 1 Atom 2 Total Difference

Learning Check What process creates energy in the Sun? Fusion of hydrogen into helium in the Sun’s core generates the Sun’s energy. How long ago did fusion generate the energy we now receive as sunlight? Fusion created the energy we receive today about a million years ago. This is the time it takes for photons and then convection to transport energy through the solar interior to the photosphere. Once sunlight emerges from the photosphere, it takes only about 8 minutes to reach Earth.

Light is an electromagnetic wave. Remember how I said in chapter 4 that light was an electromagnetic wave or electromagnetic energy. Light travels at the speed of 3.0 x 108 m/s = c. Amplitude is the height of the wave from the origin to the crest. Speed of light = 3.0 x 108 m/s = c Light is an electromagnetic wave.

l l Frequency is represented in hertz, or one cycle or peak per second. The number of wave peaks that occur in a unit time is called the frequency of the wave (n) nu. Frequency is represented in hertz (Hz) = 1 cycle (peak) /second.

The distance between the peaks is called the wavelength (l) lambda. l = c / n - This is the relationship between the wavelength and frequency Remember that the peaks must be on the same side (for this it would be the pointy peaks shown and not the smooth peak on the opposite side). Frequency is equal to the amount of peaks per second and is represented by Hertz (1/sec) = n. The distance between the peaks is called the wavelength (l) lambda.

Higher Energy Lower Energy Then I went through all the different types of electromagnetic waves such as the high energy to the low energy waves. Higher Energy Lower Energy

Wavelength of Visible Light in nanometers And I showed you how light was a specific region of the electromagnetic wave energy spectrum. This was to show you that light acts like waves! Wavelength of Visible Light in nanometers

Wavelength Demo

Radiant Energy Solar energy is radiation produced by nuclear fusion inside the sun’s core. It takes millions of years for the energy in the sun’s core to make its way to the solar surface. It takes 8 minutes to travel 93 million miles to earth. (186,000 miles per second) The Greenhouse effect traps some of the heat making life on earth possible.

A car is a good example of how solar energy can be collected and put to use. Because solar energy is radiant energy, no heat from the sun travels to the earth. The radiant energy turns into thermal energy (heat) when it is absorbed by molecules on Earth. In a car, the insides of the car(sets, floors, walls, etc.) absorb sunlight and change it to heat. The glass window lets the light in but does not let the heat out.

Diffraction Demo

What is process that creates a nuclear bomb? A) Fusion B) Fission C) Waves D) Geothermal

What process creates energy for the Sun? A) Fusion B) Fission C) Energy D) Geothermal

What is formula of converting matter to energy? A) E = MC2 B) V = λf C) F = 2n D) E = mv

What is the formula for determining a wavelength? A) E = MC2 B) V = λf C) F = 2n D) E = mv

What is the wavelength of a light wave that has a frequency of 10 x 10 10 Hz A) 1 x 10 7 nm B) 5.1 nm C) 2.3 x 10 5 nm D) 6.2 nm

Final Assessment 1) Describe the difference between fusion and fission draw a picture of both.

How does solar energy reach the Earth?