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# Electricity - PowerPoint PPT Presentation

Electricity. Chapter 7. Physical Science. Static electricity Conductor Insulator Conduction (charging by contact) Induction Electroscope Voltage Circuit. Current Dry cell Wet cell Resistance Ohm Series circuit Parallel circuit Circuit breaker. Vocabulary for Electricity.

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### Electricity

Chapter 7

Physical Science

Conductor

Insulator

Conduction (charging by contact)

Induction

Electroscope

Voltage

Circuit

Current

Dry cell

Wet cell

Resistance

Ohm

Series circuit

Parallel circuit

Circuit breaker

Vocabulary for Electricity

• All matter is made up of ATOMS

• An atom is the smallest part of an element that has all the properties of that element

• Atoms are made of smaller particles called “subatomic particles”

• These particles include protons, neutrons and electrons

• Both protons and electrons have a basic property called “electric charge”

Helium Atom

N

P+

P+

E-

E-

N

Nucleus of atom

Contains protons and neutrons

Is positively charged

Energy level

Contains electrons

Has a negative charge

P+

• Protons are positively charged

• Electrons are negatively charged

• Neutrons have no charge

• Opposite charges attract each other and can cause a force of push or pull

• An atom has no overall charge – why?

• Equal number of protons and electrons causes this to be true.

• Protons cannot move, but electrons can move freely

E -

N

An electric field is a region surrounding a charged particle where other charged particles are affected

A force of attraction occurs if there is an opposite charge.

A force of repulsion occurs if there is the same charge

An electric field is the strongest near a charged particle

The electric field is weaker when it is far away

So the strength of an electric field depends upon the distance from the charged particle

Electric Fields

• The word “static”, means not moving or stationary

• Static electricity is a build up of electric charges on an object

• The three ways electric charges can build are, friction, conduction, and induction

• Friction – Electrons are held loosely so rubbing a balloon against a cloth will transfer the electrons to the balloon.

• Conduction – Direct contact is required for electrons to move through a conductor

• Induction – No contact is necessary. Rearrangement occurs as repulsion and attraction work together to cause a charge

• A great example of a dramatic natural static electrical discharge is lightning.

• An electroscope is an instrument that detects a static charge.

• Static charges like to return to the ground and try to balance themselves. (grounding)

• We use grounding rods called lightning rods on our homes to protect them from lightning. Ben Franklin invented these devices for us.

• There are six types of lightning. Heat, sheet, fork, bead, ribbon, and ball.

• Rapid expansion of the air from the heat of the spark is what causes the thunder we hear.

• Lightning can travel from ground to cloud, cloud to cloud, or cloud to ground.

• Conditions needed for lightning to flourish are warmth and humidity.

• Around the world there are 100 lightning strikes every second.

• Weather meteorologists use an instrument called an interferometer to track electrical fields.

• An average of 3 people per year are struck by lightning while talking on the telephone.

• A lightning bolt is about an inch in diameter.

• 4 out of 5 people struck by lightning will survive.

• Lightning will always take the path of least resistance.

• The measure of energy that is used to move electrons is called voltage.

• Voltage is also known as “potential difference”.

• Voltage is the push that makes electrons move.

• The higher the voltage, the more energy the electrons carry. More voltage – more energy.

• The more energy each electron has, the more work can be done.

• The unit used for measuring voltage is the “volt”.

• A voltmeter is used to measure voltage.

• The letter “V”, is used to represent voltage.

• The flow of electrons through a wire is called electric current.

• Current is measured by how many electrons pass a given point in one second.

• High current – more electrons.

• The symbol for current is the letter “I”.

• The unit used to measure current is the ampere (A).

• Ammeters and galvanometers are used to measure current.

• One amp is the amount of current that flows past a given point in one second.

• Resistance - The opposition to the flow of electricity.

• Symbol for resistance is the letter “R”.

• The unit for resistance is the Ohm.

• Some materials conduct better than other materials.

• Poor conductors will have a high resistance to the flow of electricity.

• Some materials are nonconductors and are used as insulators.

• Resistance is also affected by a wires thickness, length and temperature. How?

• Longer wire – more resistance

• Thinner wire – more resistance

• Can you think of a reason resistance might be good to use?

• While slowing down the flow of electrons, heat and energy are released, sometimes used for heating elements or filaments in light bulbs.

• Super conductors often need extremely cold temperatures to work efficiently.

Ohm’s Law(law of electrical resistance)

• Ohm’s law states that the current in a wire is equal to the voltage divided by the resistance.

• Current = voltage/resistance

• I=V/R

• What would happen if the resistance increases and the voltage stays the same?

• What would happen if the resistance decreases and the voltage stays the same?

• What must happen to the resistance if the voltage increases and the current stays the same?

• We must have a source of electrons to produce a current

• Electrochemical cells provide a steady supply of electric current from a chemical reaction occurring in the cell.

• Dry Cells – Are not really dry, but contain a paste that reacts with the zinc container. Electrons then travel to the carbon rod in the center for our use.

• Electrons flow from the negative terminal to the positive terminal of a battery.

• Negative charges build up on the negative terminal and then flow through the machine to reach the positive terminal of the battery.

• Wet Cells – (also called voltaic cell) Metal plates called electrodes,(copper and zinc), are placed in an electrolyte, usually a type of acid.

• The chemical reaction between the electrodes and the acid causes electrons to pile up on the zinc electrode which is negatively charged.

• Electron pressure pushes the electrons from the zinc plate to the copper plate which is positively charged.

• The wire connecting the two electrodes gives us the pathway for a steady flow of electric current.

• Thermocouple is a device that changes heat energy into electrical energy.

• If the ends of a piece of copper wire and iron wire are joined and one of the connections is heated while the other is cooled, we will be able to produce a current.

• The greater the difference in temperature, the greater the current.

• Thermocouples are used in cars, ovens, and gas furnaces.

• Electrons moving through a wire can move in the same direction or they can travel back and forth.

• Direct Current – (DC) Electrons always flow in one direction – negative to positive.

• Alternating Current – (AC) Electrons reverse their direction regularly.

• The current in your home is ACand changes direction about 60 times per second or 60 cycles per second.

• In order to flow, electrons need a closed path through which to travel.

• An electric circuit provides a complete, closed path for an electric current.

• Parts of a circuit include, load or resistance, wires and a switch.

• Load – The device that uses the electric energy. Usually offers some resistance to the flow.

• Switch – Opens and closes the circuit. Electricity cannot flow through an open circuit.

(Simple series)

Switch

Battery

-

+

-

+

The different parts of a parallel circuit are on separate branches. Therefore, each can work independent of the other.

• Power – The rate at which work is done or energy is used.

• Electric power – The measure of the rate at which electricity does work or provides energy.

• Power = Voltage x Current or P=V x I

• Also can be written; Watts= Volts x Amperes

• According to this formula, one watt of power is delivered when a current of one ampere flows through a circuit whose voltage is one.

• The formula for electric energy is: energy = power x time, or, E = P x t

• The unit for energy from electricity is “kilowatt hours”.

• Large quantities of power must be measure in kilowatts or units of 1000 watts.

• So, kilowatts times hours = kilowatt hours

• Fuses are designed to protect your circuits by burning out if too much current is flowing at once.

• Circuit Breaker – Takes the place of a fuse by turning off the power if too much current runs through them at once.

• Fuses must be replaced, but circuit breakers can be reset.

• Respect electricity because it will always take the easiest path to ground, which could be through your body.

1) Look at each circuit diagram below.2) Do you think the bulb(s) will light? If you do, put a tick in BOX A under the diagram. If not, put a cross.3) Now make the circuit using the equipment. Does the bulb light? If it does, put a tick in BOX B. If not, put a cross.4) Repeat this for all of the circuit diagrams. Then compare your predictions (BOX A) to your results (BOX B).

Box A

Box B

Box A

Box B

Box A

Box B

Box A

Box B

Box A

Box B

Box A

Box B

Box A

Box B

Box A

Box B

Box A

Box B

Created by Mark Warner - Teaching Ideas for Primary Teachers - http://www.teachingideas.co.uk