# 30/04/2015 Static electricity and Electricity. Static electricity Lesson 1 30/04/2015.

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30/04/2015 Static electricity and Electricity

Static electricity Lesson 1 30/04/2015

Lesson 1+ 2 aims Static electricity Examples and uses of static electricity Electricity Circuits Voltage and current 30/04/2015

Static electricity Lesson 1 30/04/2015

Static electricity 30/04/2015 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 Electricity

Only 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 30/04/2015

Static Electricity

Practical 1 Blow a balloon up, tie end up. Rub balloon on jumper or top Stick to wall 30/04/2015

Practical 2 Rub plastic strips with various cloths See which one produces static electricity Try balloon and plastic strips near water 30/04/2015

Repel or attract 30/04/2015 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 repel

Opposite charges attract

Static Electricity

Practical 3 Van de Graaff 30/04/2015

Use and examples 30/04/2015 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 Precipitator Electrostatic precipitator

Static Electricity Static electricity

Static Electricity Static electricity

Quiz Quiz

Lesson 2 Electricity Circuits Current Voltage Resistance 30/04/2015

Circuit Symbols Circuit symbols

Switches - series circuit Switches – series circuit

Switches - parallel circuit

Conduction in metals 30/04/2015 1.Metals are good conductors of electricity because they have delocalised electrons which can carry the current.

Conduction in Metals Conduction 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 liquids

Electric current 30/04/2015 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 current 5.Increasing the Resistance will decrease the current

Current in a Series Circuit

30/04/2015 Current in a series circuit If the current here is 2 amps… 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

30/04/2015 Current 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 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 30/04/2015

Current in a Series Circuit

Voltage or P.D 30/04/2015 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

30/04/2015 Voltage in a series circuit V VV If the voltage across the battery is 6V… …and these bulbs are all identical… …what will the voltage across each bulb be? 2V

30/04/2015 Voltage in a series circuit V V If the voltage across the battery is 6V… …what will the voltage across two bulbs be? 4V

30/04/2015 Voltage in a parallel circuit If the voltage across the batteries is 4V… What is the voltage here? And here? VV 4V

P.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 30/04/2015

Summary 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”

30/04/2015 An example question: V1V1 V2V2 6V 3A A1A1 A2A2 V3V3 A3A3

Answer voltage V1-3v V2-3v V3-3v current A1-1.5A A2-1.5A A3-3A 30/04/2015

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

30/04/2015 Georg Simon Ohm 1789-1854Resistance 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 circuits Series – total resistance is equal to sum of all individual resistances (R=R 1 +R 2 ) Parallel-1/R = 1/R 1 +1/R 2 etc 30/04/2015

Calculate Q1. 1V, 1A calculate resistance Q2. Resistance =5 ohms, I = 2.5A V=? Q3.V=1.5V, Resistance=10ohms, I=? 30/04/2015

Resistance Resistance

Lesson 3 I-V graphs Conductors 30/04/2015

Series Circuit – 1 bulb

Series circuit – 2 bulbs Series circuits – 2 bulbs

Parallel Circuit

Ohmic conductors R is constant Provided temperature is constant, current is directly proportional to the potential difference across it. 30/04/2015

I-V for ohmic conductor 30/04/2015

Graphs 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 30/04/2015

explanation 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 30/04/2015

Resistance of Components

Quiz Quiz

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