Electricity

Francis Hawksbee:

• Performed spectacular experiments

• Created a machine that put out candles whilst they were lit

• Never realised the significance of his experiments

• He had started the electric revolution

Stephen Gray:

• Saw electrical sparks leap from the silk

• Lived in London in Charterhouse

• Built a wooden frame and suspended two beams with silk, had a hawksbee machine for generating static electricity

• He saw that Electricity could move

• It could flow through some things but not through others

• Divided world into two substances - insulators and conductors

• Battery life

• Efficiency

• Internal resistance

• Shelf life

• Energy density

• Cost

• Both batteries and fuel cells convert chemical energy into electrical energy (1.6)

• Primary cells are batteries that employ non reversible chemical reactions and therefore cannot be recharged (1.6)

• Secondary cells are batteries that employ reversible chemical reactions that allow them to be recharged (1.6)

• Fuel cells use chemical reactions that continuously consume a fuel to produce electricity (1.6)

• Electricity is the movement of charged particles

• Electrons are charged particles

• Electrons are free to flow in metals

• The acid in the fruit is caused by H+ ions being present (this is what the H means in pH)

• The electrons in the metal will flow into the acid to neutralize the H+ions

• Because the electrodes are two different metals that are placed on different parts of the reactivity series, the electrons will flow more readily from one metal than the other

• This causes a net movement of electrons in the circuit, i.e. a current

• With an increased understanding of chemical reactions and cell design, portable supplies of electrical energy have been made increasingly smaller and more efficient to meet the increased in portable electrical devices and the demands for smaller, lighter, longer lasting energy sources. But the increased volumes produced cause other problems

• Cost issues led to the development to rechargeable batteries which results in a large reduction of primary cells

• Disposal of batteries and the effect on the environment is a global issues giving rise to legislation and recycling schemes in different parts of the world.

Electric current can be direct (DC) in which electrons move in one direction or alternating (AC) current the electrons oscillate rapidly back and forth. A generator can be designed to produce either AC or DC.

Alternating current is when current changes direction

Direct current is when current flows in one direction

The role of the transformer in the national grid is to change the voltage. Depending on the type of transformer it can make the voltage higher, or lower.

A transformer is an electrical device that changes the voltage of an AC supply. A transformer changes a high-voltage supply into a low-voltage one, or vice versa.

• A transformer that increases the voltage is called a step-up transformer

• A transformer that decreases the voltage is called a step-down transformer

Step-down transformers are used in mains adapters and chargers for mobile phones and CD players.

The National Grid

When a current flows through a wire, some energy is lost as heat. The higher the current, the more heat is lost. The National Grid transmits electricity at a low current to reduce these losses. This requires a high voltage.

Power stations produce electricity at 25,000V. Electricity is sent through the National Grid cables at 400,000V, 275,000V and 132,000V.

Step-up transformers at power stations produce the very high voltages needed to transmit electricity through the National Grid power lines. This is because high voltages improve efficiency by reducing heat loss in the power lines. But high voltages are too dangerous for use in the home, so step-down transformers are used locally to reduce the voltage to safe levels. Power lines and substations are potentially dangerous as an electric shock can kill someone who gets too close to such a high voltage supply

Why are they important?

The major usage of transformer is to either to vary relative voltage of the circuit or isolate it. Transformers can convert power at one voltage into power at another voltage. Electrical power needs to be at a high voltage for transmission over distances, but must be transformed to a lower voltage for use in the home.

AC has been used for large scale distribution for domestic and industrial use owing to the need for high voltages for efficient distribution.

Energy is distributed at high voltage through a supply network and the voltage reduced by transformers before delivery to the end user.

The Movement of a conductor through a magnetic field produces an electric current. This Discovery by Faraday lead to a greater understanding of fields and an application of a more mathematical language.

Nuclear Fission is a process that uses atoms to generate VAST amounts of energy

How does it Work?

To begin with, we have a simple Uranium nucleus. Uranium is used because it is already unstable. A slow moving neutron is fred at the Uranium

The neutron attaches itself to the Uranium and makes it even more unstable!

The unstable Uranium splits into two smaller nuclei, releasing energy in the process- the two smaller nuclei are barium and krypton.

Along with the energy some more neutrons are also released!

These fission reactions produce a lot of energy and are used in nuclear generators. However each fission reaction produces more and more neutrons

WHY MIGHT THIS BE BAD?

Each of the neutrons can cause more fission reactions, releasing more energy and more neutrons. The reaction can soon become an uncontrollable chain reaction, and when that happens, an explosion takes place

• Nuclear fission is the process where the nucleus of an atom splits into several smaller fragment. The final total mass is less than the initial mass; the difference in mass (mass deficit) appears as energy. (2.4)

• Controlled fission is used for nuclear power and uncontrolled fission for nuclear weapons. The converted mass appears as kinetic energies of the fragments and as excited energy states of the products.

• Sustained nuclear fission provides the nuclear power used to generate electrical energy by means of conventional steam turbines and generators.

You need to Know

• Electricity is a secondary energy source as it is generated by non renewable primary sources of energy

• In a power station, the primary energy source drives a turbine (either directly- wind, or indirectly - steam from the combustion of fuels) which rotates the generator coils to produce a current

• Coal powered steam engines were the initial sources of energy for generators but more recently there has been a shift to oil, gas and nuclear power

• The use of computer modelling has allowed for the development of even more efficient power generation using a wider variety of primary energy sources to cater for differing locations and access to natural resources.

Advantages:

• Large amount of energy produced per acre of land used.

• Lots of technological advances still to be made will increase efficiency, safety.

• Small amount of fuel can produce a huge amount of energy.

• Nuclear fission could solve a lot of the disadvantages.

• Low emissions source of reliable and constant power generation.

• Future Thorium reactors or progress on nuclear fusion could eliminate these concerns.

Disadvantages:

• Safety concerns due to potential for uncontrolled reactions.

• Waste byproducts must be stored properly to avoid impact on environment.

• Fuel source is limited making it a non-renewable energy source and unsustainable.

• Waste from some reactors can be used to produce weapons grade materials for nuclear weapons.

• Waste will remain toxic for long periods after use.