Static Circuits Mains Electricity

Objectives Identify common materials which are electrical conductors or insulators, including metals and plastics. Explain how insulating materials can be charged by friction. Recall that there are forces of attraction between unlike charges and forces of repulsion between like charges.

Electric Charge Atoms are made of protons, neutrons, and electrons. The electrons have a negative electric charge.

Static Electric Charge Electrons can be transferred from one material to another. - - + + - + - - - + + - + - + - + - + - + - + - + - + - + - + - + - + + +ve charge -ve charge

Static Electric Charge Opposite charges attract. Like charges repel. + - + + - -

Electrostatic Phenomena Acetate Rods Polythene Rods - + - - + - - + - + + + - + - - + - - + - + + + - + - + - - + - + - - + - - + - - + - + + - + + - + + + - + - + - - + - + - - + - - + - - + - + - + + - + + + + - + - - + - - + - + + + Cloth +ve charge - + - Cloth -ve charge - + - - + - + + + Acetate Rod +ve charge Polythene Rod -ve charge

Electrostatic Phenomena Why do electrically charged balloons stick on the wall?

Electrostatic Phenomena Why do electrically charged combs pick up pieces of paper?

Objectives Explain electrostatic phenomena in terms of the movement of electrons. Recall the potential dangers of electrostatic charges, e.g. when fuelling aircraft and tankers. Recall some uses of electrostatic charges, e.g. in photocopiers and inkjet printers.

Dangers of Static

Uses of Static

Uses of Electrostatics Spray Painting.

Uses of Electrostatics Inkjet Printers

Uses of Electrostatics Photocopiers See ActiveBook Animation

Uses of Electrostatics Electrostatic Precipitators

Uses of Electrostatics Electrostatic Precipitators Smoke With Dust Particles Removed Earthed Metal Plates - Smoke & Charged Dust Particles - - - - - - Metal Mesh -50 000 V Smoke & Dust Particles

The Gold Leaf Electroscope Use to detect charge. Gold leaf is extremely thin and able to move. Metal Plate Gold Leaf Metal Rod

The Gold Leaf Electroscope + + - + - + - + - + - - - + + - - + - - + +

The Gold Leaf Electroscope + + - + - + - - - + - - + - - + + + + - + -

Can you correct his mistakes? Chris’s Homework Atoms contain neutrons and two charged particles, protons (negative) and electrons (positive). Conductors can be ‘charged by friction,’ a process where one material loses protons to another material. Like charges attract, and opposite charges repel. Aeroplanes have to be earthed to ensure there is no static charge around when they are refuelling. Uses of static electricity include laser printers, photocopiers, and setting fire to F1 drivers. Can you correct his mistakes?

Learning Objectives Identify common circuit symbols. Identify electric current as a flow of charge/electrons. Explain how current behaves in series and parallel circuit.

Circuit Symbols Cell Battery Bulb Resistor Ammeter Voltmeter Switch LDR Thermistor Variable Resistor Fuse

(Two or More ‘Branches’) Series and Parallel Series (One Complete Loop) Parallel (Two or More ‘Branches’)

Electrical Current Electrical current is the flow of electrical charge. The charge comes from the electrons.

Electrical Current Electrons flow around the circuit. They gain energy from the cell, and transfer energy to other components. Inside Circuits

Measuring Current Ammeters must be placed in series. They need to measure the current flowing through them.

Electrical Current A2 1 A A1

Electrical Current 4 A A3 A1 A2

Electrical Current 6 A A4 A1 A2 A3

Electrical Current 3 A A3 A1 A2

Learning Objectives Define current as the rate of flow of charge. Identify electrons as the charge carriers in electrical circuits. Identify, use, and explain the equation I = Q/t.

Electrical Charge Protons and electrons both have electrical charge (positive and negative). Charge is measured in coulombs, C. One coulomb of charge is the equivalent of 6.25 billion billion electrons! (6 250 000 000 000 000 000) Charge has the symbol Q.

Electrical Current Current is the rate of flow of charge (how much charge flows in a certain time). Current is measured in amps. One amp is equal to one coulomb of charge passing a point every second. Current = Charge / Time Taken I = Q / t

Electrical Current Questions I = Q / t 10 C of charge pass a point in 5 seconds. What is the current? A current of 3 A flows for 10 seconds. How much charge flowed past each point? How long will it take for a 100 C of charge to flow past a point when the current is 2 A?

Electrical Current The ______ in a circuit is a measure of how much ________ is flowing. Current is measured in ____. A higher current means more ______ is flowing past a point every ______. A current of one amp equals one _______ of charge flowing past a point every second. The total current entering a ______ must _____ the total current _______ a junction. Words: second junction exiting current charge amps equal electricity coulomb

Learning Objectives Explain the term ‘Potential Difference.’ Explain how potential difference behaves in series and parallel circuits.

Potential Difference Initial GPE Potential Difference Final GPE

Potential Difference 0 V 1.5 V pd 0 V 1.5 V

Recording Potential Difference

Investigating Potential Difference You will need: 2 x Cells. 3 x Bulbs. 10 x Connecting Wires.

Investigating Potential Difference Series Parallel

Investigating Potential Difference Back

Investigating Potential Difference Back

Potential Difference 100 J 80 J 60 J 40 J 20 J 20 J 20 J -20 J -20 J pd pd pd 20 J 20 J 20 J

Potential Difference 100 J 80 J 60 J 40 J 20 J 20 J 20 J 0 V 0.5 V pd pd pd 0 V 0.5 V 0.5 V 1.0 V 1.0 V 1.5 V

Potential Difference 1.5 V

Potential Difference 1.5 V

Potential Difference 1.5 V 1.5 V

Potential Difference 3 V 3 V

Potential Difference 9 V 4.5 V

Potential Difference 3 V 3 V

Potential Difference 1.5 V

Potential Difference 1.5 V

Potential Difference 1.5 V

Potential Difference The _________ _________ of a component is a measure of how much _____ is _________ in the component. The potential difference across the ____ must _____ the ___ of the potential differences across the components in a ______ circuit. Words: series cell transferred energy equal sum potential difference

Current & pd Summary is equal splits up In a series circuit: Current _________ at any point. Potential difference _________ over each component. In a parallel circuit: Current __________ down each branch. Potential difference ________ across each branch. is equal splits up

Learning Objectives Identify that an increase in resistance will reduce the electrical current. Explain how the resistance of LDRs and thermistors change with light intensity and temperature. Determine Ohm’s Law.

Resistance Which of these materials will have the highest resistance? Wood Metal

Add a second bulb and record the new current. Resistance You will need: two cells. two bulbs. a multimeter. 5 connecting wires. Connect this circuit and record the current: Add a second bulb and record the new current. A

Resistance Resistance is anything that will resist a current; i.e. it makes it harder for electricity to flow. It is measured in ohms, Ω. It has the symbol R.

Resistance All components in electrical circuits have ________ – even the ____! Some components, like _____, have a ____ resistance. The ____ wire in the _______ makes it harder for the current to flow. Putting more bulbs in _____ will increase the resistance and ______ the current. Words: resistance increase thick thin decrease filament series high low wires bulbs

Measuring Small Currents Milliammeters must be placed in series. They need to measure the current flowing through them.

Diodes A diode only lets ________ flow in one __________ – it has very high __________ in the other direction. 0.6 V Words: direction current resistance

Light Dependent Resistors Light dependent resistors (____) have a ____ resistance in the dark. When _____ shines on the LDR it has a ___ resistance. This makes it easier for _______ to flow. Words: high current LDRs low light

Thermistors Thermistors have a ____ resistance when they are cold. When they ____ up they have a ___ resistance, making it easier for current to flow. The increase in ___________ increases the number of free _________ available. Words: high current heat low electrons temperature

Thermistor – resistance DECREASES when temperature INCREASES Comparison Light dependant resistor – resistance DECREASES when light intensity INCREASES Thermistor – resistance DECREASES when temperature INCREASES Resistance Amount of light Resistance Temperature

Straight Line Graphs 6 6 Gradient = Rise / Run Gradient = 6 / 6

Straight Line Graphs 12 6 Gradient = Rise / Run Gradient = 12 / 6

Straight Line Graphs 3 6 Gradient = Rise / Run Gradient = 3 / 6

Resistance I.e. If you double the potential difference, the current doubles The graph shows that current is directly proportional to potential difference. This is known as Ohm’s Law.

Resistance General equation for a straight line graph is: y = mx + c. y = Voltage (V) x = Current (I) m = Gradient The gradient is also equal to the resistance (R). Therefore, V = IR

Resistance Questions V = IR What is the resistance of the following: A bulb with a voltage of 3 V and a current of 1 A. A resistor with a voltage of 12 V and a current of 3 A A diode with a voltage of 240 V and a current of 40 A A thermistor with a current of 0.5 A and a voltage of 10 V

Learning Objectives Identify the unknown resistance of a resistor. Plot and explain the Current/Potential Difference graph for a filament bulb.

Mystery Resistance! Calculate the resistance of one of the resistors.

Filament Bulbs 3 V A V

Resistance As the wire heats up the resistance increases.

Filament Bulbs As voltage increases the bulb gets hotter and resistance increases

Filament Bulbs Be aware...

Learning Objectives Explain the difference between conventional current and electron flow. Plot and explain the Current/Potential Difference graph for a diode.

Diodes 5 V mA V

Resistance of a Wire Plan an experiment to find the resistance of a wire. Apparatus. Circuit diagram. Safety precautions (voltage?). What measurements will you take? What will you do with your results? How will you know if it is an ohmic conductor?

Mains Electricity To consumer unit

Mains Electricity Earth wire Live wire Fuse Neutral wire Cable grip Insulation

Mains Electricity The live wire has alternating current (AC) flowing through it. The neutral wire completes the circuit. Earth wire Neutral wire Insulation Live wire Fuse Cable grip

Mains Electricity The earth wire is a safety device. There is usually no current flowing through it unless an appliance develops a fault. Earth wire Neutral wire Insulation Live wire Fuse Cable grip

Mains Electricity

Mains Electricity

Mains Electricity

Mains Electricity

Mains Electricity

Mains Electricity

Mains Electricity

The Earth and Fuse Wires Write a short paragraph explaining: Which wires the mains electricity usually flows through. What happens to the circuit when the live wire is damaged. What happens to the resistance of the circuit. What happens to the current. What happens to the fuse wire.

Can you correct his mistakes? Chris’s Homework Cables for mains electricity have three wires; positive, negative, and earth. The current usually flows through all three wires in series. If the live wire becomes connected to the casing of an appliance the current no longer flows through the earth wire. This reduces the resistance of the circuit and causes more current to flow. The increased current causes the fuse wire to melt, breaking the circuit. Can you correct his mistakes?

Mains Electricity

Hazards

V DC stands for “Direct Current” – the current only flows in one direction: Time 1/50th s AC stands for “Alternating Current” – the current changes direction 50 times every second (frequency = 50Hz) 230V T V

Alternating Current

Power

Power = Current x Potential Difference A watt is a unit of power. Power is defined as the amount of energy transferred per unit time. I.e. It is the amount of energy transferred each second One watt is equal to one joule per second. I.e. 1 W = 1 J/s Power = Current x Potential Difference

Power = Current x Potential Difference P = I x V J C J C J _ _ _ ___ = x = s s C C s

Power If we know two of the three values we can work out the third. For mains electricity in the UK the voltage is 240V. The power rating is often shown; i.e. a 60W bulb or a 1.2kW kettle. We can therefore calculate the current flowing through the appliance.

Challenge Use the information provided on the appliances to calculate the unknown. For example, if the appliance has a power rating (i.e. You know how many watts it uses) and a voltage rating, you can calculate the current. Record your calculations in your notes.

Questions P = IV Copy and complete the table. Appliance Power rating (W) Voltage (V) Current needed (A) Fuse needed (3, 5 or 13A) Toaster 960 240 Fire 2000 Hairdryer 300 Hoover 1000 Computer 100 Stereo 80

Energy & Power If the power is the amount of energy transferred every second, the total energy will be: Energy = Power x Time E = P x t Example: If a 1200W kettle is used for 3 minutes, what is the total energy transferred? A. E = P x t = 1200 W x 180 s = 216,000 J or 216 kJ

Questions What is the power rating of a light bulb that transfers 120 J of energy in 2 seconds? What is the power of an electric fire that transfers 10,000 J of energy in 5 seconds? How much energy does a 150W light bulb transfer in a) one second, b) one minute?

Energy = Current x Potential Difference x Time Energy & Power Since power = current x potential difference: Energy = Power x Time Energy = Current x Potential Difference x Time E = I x V x t Example: How much energy is transferred to a 1.5 V bulb if a current of 1 amp flows for 10 seconds? A. E = I x V x t = 1 A x 1.5 V x 10 s = 15 J

Questions How much energy is transferred to a 12 V bulb when a current of 2 A flows for 30 seconds? How much energy is transferred to a 24 V bulb when a current of 4 A flows for 40 seconds? How much energy is transferred to a 12 V bulb when a current of 2 A flows for 2 minutes?

Revision – 2.10 1 A 2 A 3 A 4 A

Revision – 2.10 1 A 0.5 A 1 A 2 A 10 Ω 5 Ω