30/04/2015 static electricity and electricity. static electricity lesson 1 30/04/2015

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Static Static electricity and electricity and

ElectricityElectricity

Static electricityStatic electricity

Lesson 1

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Lesson 1+ 2 aimsLesson 1+ 2 aims

• Static electricity• Examples and uses of static

electricity• Electricity• Circuits• Voltage and current

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Static electricityStatic electricity

Lesson 1

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Static electricityStatic electricity18/04/23

1. When two different insulating materials are rubbed together they become electrically charged.

2. Negative charges (electrons) rub off one material onto the other. The material which gains negative charges becomes negatively charged. The material which loses negative charges becomes positively charged.

Static ElectricityStatic ElectricityStatic ElectricityStatic Electricity

Static ElectricityStatic Electricity

Only electrons moveOnly electrons move

• Both positive and negative charges are produced by the movement of electrons

• Positive charges do not move• A positive static charge is caused

by electrons moving away

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Static ElectricityStatic ElectricityStatic ElectricityStatic Electricity

Static ElectricityStatic Electricity

Practical 1Practical 1

• Blow a balloon up, tie end up.• Rub balloon on jumper or top• Stick to wall

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Practical 2Practical 2

• Rub plastic strips with various cloths

• See which one produces static electricity

• Try balloon and plastic strips near water

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Repel or attractRepel or attract18/04/23

1. Electrically charged objects can attract small objects

2. Two positively charged objects will repel

3. Two negatively charged objects will repel

4. A positively charged object and a negatively charged object will attract

Like charges repelLike charges repelLike charges repelLike charges repel

Like charges repelLike charges repel

Like charges repelLike charges repelLike charges repelLike charges repel

Like charges repelLike charges repel

Opposite charges attractOpposite charges attractOpposite charges attractOpposite charges attract

Opposite charges attractOpposite charges attract

Static ElectricityStatic ElectricityStatic ElectricityStatic Electricity

Static ElectricityStatic Electricity

Practical 3Practical 3

• Van de Graaff

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Use and examplesUse and examples18/04/23

1. Static electricity can be used in photocopiers, smoke precipitator, and spray painting

2. A charged object can be discharged by connecting it to earth with a conductor

3. Static electricity can be dangerous (e.g. lightning). If the voltage becomes too great the negative charges can jump a gap causing a spark. This spark could ignite a flammable liquid nearby.

Electrostatic PrecipitatorElectrostatic PrecipitatorElectrostatic PrecipitatorElectrostatic Precipitator

Electrostatic precipitatorElectrostatic precipitator

Static ElectricityStatic ElectricityStatic ElectricityStatic Electricity

Static electricityStatic electricity

Static ElectricityStatic ElectricityStatic ElectricityStatic Electricity

Static electricityStatic electricity

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Lesson 2Lesson 2

• Electricity• Circuits• Current• Voltage• Resistance

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Circuit SymbolsCircuit SymbolsCircuit SymbolsCircuit Symbols

Circuit symbolsCircuit symbols

Switches - series circuitSwitches - series circuitSwitches - series circuitSwitches - series circuit

Switches – series circuitSwitches – series circuit

Switches - parallel circuitSwitches - parallel circuitSwitches - parallel circuitSwitches - parallel circuit

Switches - parallel circuitSwitches - parallel circuit

Conduction in metalsConduction in metals18/04/23

1.Metals are good conductors of electricity because they have delocalised electrons which can carry the current.

Conduction in MetalsConduction in MetalsConduction in MetalsConduction in Metals

Conduction in metalsConduction in metals

1.Ionic compounds conduct electricity when molten or dissolved in water. The current is carried by charged particles called ions.

2.The positive ions (cations) attract to the negative electrode (cathode)

3.The negative ions (anions) attract to the positive electrode (anode)

4.At the electrodes the ions can lose their charge and form new substances.

5.This process is called electrolysis

Conduction in liquidsConduction in liquidsConduction in liquidsConduction in liquids

Conduction in liquidsConduction in liquids

Conduction in liquidsConduction in liquidsConduction in liquidsConduction in liquids

Conduction in liquidsConduction in liquids

Electric currentElectric current18/04/23

1.Electric Current is the flow of charge

2.Current can be measured using an ammeter (connected in series)

3.Current is measured in Amps (A)4.Increasing the Voltage will

increase the current5.Increasing the Resistance will

decrease the current

Current in a Series CircuitCurrent in a Series CircuitCurrent in a Series CircuitCurrent in a Series Circuit

Current in a Series CircuitCurrent in a Series Circuit

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Current in a series circuitCurrent in a series circuit

If the current here is 2 amps…

The current here will be…

The current here will be…

And the current here will be…

In other words, the current in a series circuit is THE SAME at any

point

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Current in a parallel circuitCurrent in a parallel circuit

A PARALLEL circuit is one where the current has a “choice of routes”

Here comes the current…

And the rest will go down here…

Half of the current will go down here (assuming the bulbs are the same)…

Current in circuitsCurrent in circuits

1.In a series circuit the current is the same everywhere

2.In a parallel circuit the current divides on entering a junction and rejoins on returning to the battery

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Current in a Series CircuitCurrent in a Series CircuitCurrent in a Series CircuitCurrent in a Series Circuit

Current in a Series CircuitCurrent in a Series Circuit

Voltage or P.DVoltage or P.D18/04/23

1.Potential Difference is connected to the amount of energy that is gained or lost across part of a circuit

2.Potential Difference is measured using a Voltmeter (connected in parallel)

3.Potential Difference is measured in Volts (V)

4.Potential Difference gained across a cell or battery is called Voltage

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Voltage in a series circuitVoltage in a series circuit

V

V V

If the voltage across the battery is 6V…

…and these bulbs are all identical…

…what will the voltage across each bulb be? 2V

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Voltage in a series circuitVoltage in a series circuit

V

V

If the voltage across the battery is 6V…

…what will the voltage across two bulbs be?

4V

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Voltage in a parallel circuitVoltage in a parallel circuit

If the voltage across the batteries is 4V…

What is the voltage here?

And here?

V

V4V

4V

P.D in circuitsP.D in circuits

1.In a series circuit the potential difference is shared between the components

2.In a parallel circuit the potential difference is the same across each component and equals the voltage across the battery

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SummarySummary

In a SERIES circuit:

Current is THE SAME at any point

Voltage SPLITS UP over each component

In a PARALLEL circuit:

Current SPLITS UP down each “strand”

Voltage is THE SAME across each”strand”

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An example question:An example question:

V1

V2

6V

3A

A1

A2

V3

A3

AnswerAnswer

voltage• V1-3v• V2-3v• V3-3v

current• A1-1.5A• A2-1.5A• A3-3A

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Advantages of parallel circuits…Advantages of parallel circuits…

There are two main reasons why parallel circuits are used more commonly than series circuits:

1) Extra appliances (like bulbs) can be added without affecting the output of the others

2) If one appliance breaks it won’t affect the others either

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Georg Simon Ohm 1789-1854

ResistanceResistance

Resistance is anything that will RESIST a current. It is

measured in Ohms, a unit named after me.

The resistance of a component can be calculated using Ohm’s Law:

Resistance = Voltage (in V)

(in ) Current (in A)

V

RI

Resistance in circuitsResistance in circuits

• Series – total resistance is equal to sum of all individual resistances (R=R1 +R2)

• Parallel-1/R = 1/R1 +1/R2 etc

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CalculateCalculate

• Q1. 1V, 1A calculate resistance• Q2. Resistance =5 ohms, I = 2.5A

V=?• Q3.V=1.5V, Resistance=10ohms,

I=?

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answersanswers

• 1ohm• 12.5V• 0.15A

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ResistanceResistanceResistanceResistance

ResistanceResistance

Lesson 3Lesson 3

• I-V graphs• Conductors

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Series Circuit – 1 bulbSeries Circuit – 1 bulbSeries Circuit – 1 bulbSeries Circuit – 1 bulb

Series Circuit – 1 bulbSeries Circuit – 1 bulb

Series circuit – 2 bulbsSeries circuit – 2 bulbsSeries circuit – 2 bulbsSeries circuit – 2 bulbs

Series circuits – 2 bulbsSeries circuits – 2 bulbs

Parallel CircuitParallel CircuitParallel CircuitParallel Circuit

Parallel CircuitParallel Circuit

Ohmic conductorsOhmic conductors

• R is constant• Provided temperature is constant,

current is directly proportional to the potential difference across it.

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I-V for ohmic conductorI-V for ohmic conductor18/04/23

GraphsGraphs18/04/23

1.Current-Voltage graphs can be used to show how the current flowing through a component changes with different voltages

2.The current through a resistor is directly proportional to the voltage across the resistor (at a constant temperature)

Comparing I-V graphs Comparing I-V graphs 18/04/23

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explanationexplanation

1. The resistance of a filament lamp increases as the filament gets hotter

2. A diode allows current to flow in one direction only (the diode has a very high resistance in the opposite direction)

3. The resistance of a light dependent resistor decreases with increasing light intensity

4. The resistance of a thermistor decreases with increasing temperature

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Resistance of ComponentsResistance of ComponentsResistance of ComponentsResistance of Components

Resistance of ComponentsResistance of Components

Resistance of ComponentsResistance of ComponentsResistance of ComponentsResistance of Components

Resistance of ComponentsResistance of Components

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