How photocells work...

It absorbs the suns energy and this causes electrons to be knocked loose from the silicon crystal. These electrons can now flow freely within the silicon. this flow is called an electric current.

To maximise the power output and efficient solar collector must track where the sun is in the sky but this requires extra technology and therefore more money.

Wind turbines

Wind turbines are another way of collecting energy without burning fossil fuels. They transfer the kinetic energy from the wind into electrical energy.

Harnessing the sun's energy

Light can be absorbed by a surface and transferred into heat energy. Water passed over this surface will then me heated and can be used for heating buildings.

Advantages:

• Saves money by using a free energy resource.
• Uses a renewable source
• Dosen't need much light to produce electricity
• Doesn't produce CO2 or noise pollution
• Low maintenance
• No need for power cables
• No need for fuel
• No polluting wste
• Long life

DIsadvantages:

• Expensive to buy
• Don't work at night or dak area
• Don't produce large amouts of energy

AC - Alternating current

An Alternating Current

There are two main types of current in our world. One is DC, which is a constant stream of electrons in one direction. The other is alternating current, which is a stream of charges that reverses direction. Scientists such as Charles Proteus Steinmetz andNikola Tesla made great advances when AC power was just a science experiment. 

Flowing Back and Forth

 Charges (electrons) must always be flowing to have a current. However, the flow of charges does not always have to be in one direction. In alternating current, the charges move in one direction for a very short time, and then they reverse direction. This happens over and over again. 

Scientists describe the cycle of switching directions as the frequency. Frequency is measured in Hertz (Hz). Currents thatcycle more often during a specific amount of time are said to have a higher frequency. AC power cycles 60 times per second in the US. 

Since the web is a global resource, we should also mention that there are different alternating current frequencies across the world. While we all use alternating current, the switching happens different amounts during a specific time period. Most countries use AC frequencies at either 50 hertz or 60 hertz. 

Cheaper and Stronger

Why do we use AC power all over the world? It's cheaper and easier to make devices for AC power. It is less expensive because you can increase and decrease the current for AC power very easily. The power switches for AC power are also less expensive to manufacture. Probably the biggest advantage of AC is that you can use high voltages with small currents to reduce losses when you transmit power. Remember that lost energy increases the more collisions you have, and reducing current decreases the amount of collisions (and reduces heating in the wires). You can send power with DC, but the DC power transmission loses a lot of energy. You would have to put much more effort into sending DC power over the same distance. 

DC - Direct current

There are two main types of current in our world. One is direct current (DC) which is a constant stream of charges in one direction. The other is alternating current (AC) that is a stream of charges that reverses direction. The current in DC circuits is moving in a constant direction. The amount of current can change, but it will always flow from one point to another. Before we move on, we need to explain that physicists, as well as electricians, refer to something called conventional current. Do you remember that we talked about physicists agreeing to always use positive charges to determine how electric field lines would be drawn? Following through on that agreement, they also agreed to explain charge flow in terms of positive charges rather than electrons. So although electrons would flow from negative to positive, by convention (agreement), physicists refer to conventional current as a flow from high potential/voltage (positive) to low potential/voltage (negative). Reminding you that potential is like electrical height, this means that conventional current flows "downhill", which makes sense. Electrons move from areas where there are excess of negative charges to areas where there are a deficiency (or positive charge). Electrons move from "-" to "+", but conventional current is considered to move in the other direction. When you set up a circuit, conventional current is considered to move from the "+" to the "-" side. The idea about using positive charges in forming explanations comes fromBenjamin Franklin. In Franklin's day, we didn't know about protons and electrons. Franklin believed that something moved through electrical wires, and he called these things "charge". He assumed there was only one kind of charge, and he logically assumed that charge would flow from a spot that had an excess (extra), to a spot that had a deficiency (too few). He called the spot with an excess "positive" and the spot with a deficiency "negative". So, for Franklin, charge flowed from positive to negative. We simply honor his achievements by continuing with this idea. The best real-life example of direct current is a battery. Batteries have positive (+) and negative (-) terminals. If you take a wire and connect the positive and negative terminals on a battery, the electrons in the wires will begin to flow to produce a current. You can prove that the current is flowing if you connect a small light to the circuit. The light will begin to glow as the electrons pass through the filaments. 

Red Shift:

A galaxies get further and further away from us, we can meause the wavelength and eventually the wavelength of light increases so the light shifts towards the red end of the spectrum

Cosmic background radiation

Scientists discovered that there are microwaves coming from every direction in space: this is called the cosmic microwave background radiation, or CMBR for short.

The CMBR comes from radiation created at the beginning of the universe. The Big Bang theory is the only theory at the moment that can explain the presence of the CMBR.

Comets
Comets are balls of ice and dust in orbit around the Sun. The orbits of comets are different from those of planets - they are elliptical. A comet's orbit takes it very close to the Sun and then far away again. The time to complete an orbit varies - some comets take a few years, while others take millions of years to complete an orbit.Comets have a range of different orbital periods and all leave a trail of debris behind them. Comets are often visible from Earth when they get close to the Sun, because the Sun's heat vaporises material from their surface, and this vapour forms a tail.

Asteroids
Asteroids are rocky objects, smaller than planets. Most of them are found in an 'asteroid belt', in orbit around the Sun between Mars and Jupiter. The minor planet Ceres is found here, too. Asteroids can crash into each other. When they do, they may break apart and their orbit may change.The orbits of some asteroids cross the Earth's orbit. At various times during the Earth's history, asteroids have hit the Earth. When this happened, a tremendous amount of energy was released, throwing up billions of tonnes of dust. This blocked heat and light from the Sun, making the Earth very cold.It is thought that it was the collision of an asteroid with the Earth that helped to drive the dinosaurs to extinction. Scientists worry that an asteroid could still hit the Earth and cause a global catastrophe.

Stars are formed from massive clouds of dust and gas in space.

Clouds of dust in outer space.

Gravity pulls the dust and gas together to form a protostar.

Dust clouds coming together to form a star.

As the gases come together, they get hot. A star forms when it is hot enough for nuclear reactions to start. This releases energy, and keeps the star hot.

The sun in space.

During the main sequence period of its life cycle, a star is stable because the forces in it are balanced. The outward pressure from the expanding hot gases is balanced by the force of the star’s gravity. Our Sun is halfway through its 10 billion year stable phase.

Gravity pulls smaller amounts of dust and gas together, which form planets in orbit around the star.