Science Study Sheet 2: Unit Electricity

Glossary

• Electron- a negatively charged particle. A flow of electrons is electricity
• Electric charge: negative or positive quantity of electricity that builds on an object
• Negative charge: an excess amount of electrons
• Positive charge: a shortage of electrons
• Neutral charge: when the amount of protons and electrons are equal
• Static electricity: a charge on a substance that stays in the same place
• Electrostatics: the study of static electricity charges

Electrostatics

1. All objects are neutral. They contain an equal number of positive and negative charges.
2. Everything remains neutral until it is charged
3. An object is charged when it has too little or too many negative charges. Only electrons move during the transfer of charge, the positive charges don't move.

Law of Electric Charges

1. Like charges repel one another

- - + +

1. Opposite charges attract one another

+ -

1. Both positive and negative charges attract neutral charges

+ N - N

Charging by Friction

When objects are rubbed together negative charges are transferred form on substance to another. The object with a stronger hold of electrons will gain electrons and become negative, and the other one with the weaker hold will lose electrons and become positive.

• Conductors: a substance in which electrons can move freely from one atom to another
• Insulators: a substance in which electrons cannot move freely from atom to atom

Charging by Contact

Charges can also be transferred by direct contact between substances. During contact both objects receive the same charge.

Charging by Induction

Transferring a charge form one substance to another without direct contact

Lightning

• at any given time there are approx. 2000 thunderstorms happening in the world
• 100 lightning strikes every second
• 8 million strikes a day

Lightning is a natural process where the atmosphere and the earth exchange electric charges. The electric charges are removed form the earth in a number of ways. One is evaporation.

Daily uses of static electricity

• Pollution and dust control
• Spray painting
• Fabric sheet softening

Current Electricity

• A continuous flow of charge is called current electricity
• If 1 electron flows into a bulb then 1 electron flows out

Current- the amount of charge passing a point in a unit of time

Coulomb- a group of electrons

• Current is measured in amperes
• The potential difference across an object is measured in volts

Electric Current- the flow of electrons through a conductor

Electric Circuit- the flow of electricity through a controlled pathway

The Four Parts of a Simple Circuit

1. Source of electrical energy
2. An electrical load
3. Devices to control the electric current
4. Electrical conductors for connectors

Potential Difference

When electrons move through a circuit, they use up energy. This energy is called Potential Difference or Voltage

Cells in Series and Parallel

Cells in Series

Sometimes an electrical device requires more electrical energy (voltage) then one cell can apply. In this case, the cells can be connected in series and the voltage of each cell is added together.

Cells in Parallel

A single cell operating by itself often uses up the available energy rather quickly. When cells are connected in parallel they supply the same amount of energy for a longer time.

Electrical Resistance

Resistance is the ability to impede (slow down) the flow of electrons in conductors. A resistor is an electrical device used to limit the amount of electrons flowing through in a conductor.

Symbol- R

SI unit - Ω

When electrons slow through a conductor, the electrical resistance causes a loss of voltage. This loss of voltage is referred to as electrical potential difference or a voltage drop.

Ohm's Law

The potential difference between two points on a conductor is proportional to the electric current flowing through the conductor. This only applies to ohmic resistors that are unaffected by temperature.

Potential Difference = Electric Current x Electric Resistance

V= IxR I = V/R R = V/I

V - voltage (V = volts)

I - current (A = amperes)

R - resistance (Ω = ohms)

The Series Circuit

The term series applies to any electric circuit in which parts of the circuit are wired along a single path.

The Parallel Circuit

For bulbs connected in parallel. The current passes through a separate circuit, called a branch circuit, to each bulb

Electrical Energy

Electrical energy is the energy transferred to an electrical load by moving electric charges (electrons)

Symbol - E

SI units- J (joule) / Wh (watt-hour) / kWh (kilowatt-hour)

Electric energy = voltage drop x electric current x time

E = V x I x t

Joules = volts x ampere x seconds

J = V x A x S

Wh = V x A x hours

Electric Power

Electric power is a measure of the rate at which electric energy is used

• Symbol - P
• SI unit - Watt (W)
• Electric Power = Voltage drop x Electric current
• P = V x I
• Watts = volts x amperes
• W = V x A
• Cost of Electrical Energy
• Electrical energy (kWh) = Power (KW) x time (h) or E = P x t
• Cost = Electrical energy (kWh) x Rate ($ / kWh)
• Generating Energy
• Electricity is created by a simple process. A coil of wire is spun very fast inside a magnet. This is a generator.

2 Types of Electric Current

• Direct Current - DC - The movement of a negatively charged area to a positively charged area - battery
• Altering Current - AC - The back and fourth movement of electrons created by a generator - household wiring

Nonrenewable resources

• Fossil fuel generating stations
• Nuclear generating stations

Renewable resources

• Hydroelectric (water) stations
• Solar
• Wind
• Biomass
• Tidal
• Geothermal

Energy Terms

Sustainable: refers to out ability to maintain energy sources over a long period of time

• Efficiency: comparison of the amount of energy produced and the amount of energy used
• Storage: A practical way to store electricity at the same rate it is generated
• Transmission: the movement of electricity on high voltage power lines and the problem of resistance creating loss of power
• Transformer: used to increase or decrease voltage