1. Electricity Show video clip on introduction to electricity
Write down four things you learnt from the video clip about electricity

2. Questions on Video clip
What is electricity?
What does a battery do?
What is current and what is it measured in?
What is meant by short circuit.
What is a circuit?
What happens the electic energy when a light bulb is in the circuit?
What happens the current when the light bulb is in the circuit?
Are electrons big or small?

3. Keywords

4. Lesson objectives
To be able to clearly define the meaning of the terms “current”, and “voltage / potential difference”
To be able to correctly use a voltmeter and an ammeter and an ohmmeter.
Identify basic circuit symbols.
To understand what resistors and variable resistors are and how they work.
To understand the relationship between potential difference and current.
To preform calculations using ohm's law.

5. Lesson objectives
To measure resistance of various electronic components.
To distinguish between series and parallel circuits and their effects ón light bulbs.
To know the three effects of electric current
To distinguish between a.c and d.c.
Lch. 2.

6. INTRODUCTION TO ELECTRICITY
This is a brief introduction to the main facts of electricity, potential difference, current, switches, parallel and series circuits and resistance.
In the diagram are of the common symbols for drawing electric circuits.

7. ELECTRIC CIRCUITS
An electric current is a flow of negatively charged electrons.
A circuit is a complete path along which a current may flow.
A circuit consists of materials which are conductors (usually metals), which have “free” electrons, loosely attached to atoms, which as they move from atom to atom, carry an electric charge. This flow of charge is the current.
The electrons flow when there is a difference in potential (voltage) across the wire.

8. Remember to show virtual physics lab. Demo.

9. In fact because electrons have a negative charge, current actually flows from – to +, but it is the agreed convention that currents shown in circuit diagrams flow from + to -. We call this conventional current
Insulators are materials which will not carry currents; they have no free electrons
How could you show if a material conducts electricity or not?
What apparatus would you need?
How would you connect the test substance into the ciruit.

10. Circuit to test if a substance is a conductor or an insulator.

11. Conductors and insulators
MATERIAL
CONDUCTOR
INSULATOR
Zinc
Lead
Perspex
Aluminium
Wooden ruler
Iron nail
Protractor
Brass
Polythene
Rubber band
Copper
Cardboard
Steel
Pencil lead (carbon)
Rusty nail

12. Conclusions
All metals are conductor as because the electrons are free to move.
In non metals the electrons are held tightly by the nucleus of the atom so cannot flow we call these materials insulators.
Graphite is one of the few non-metals which can conduct electricity.

13. Voltage Voltage is a measure of the energy carried by the current.
Voltage is causes the current to flow.
(Technically it is a measure of the difference in energy between two points – hence the name potential difference).
Voltage is a measure of the energy carried by the charge.
Voltage is supplied by the battery (or power supply).
We say voltage across a component.
Voltage is measured in volts, V.
Voltage is measured with a voltmeter, connected in parallel.
The symbol V is used for voltage in equations.

14. Voltage / potential difference(p.d.)
Voltage is measured with a voltmeter.
Voltmeters are always placed in parallel in a circuit.
Voltage is the driving force that pushes the current like an electric pump.
Voltmeter in parallel

15. CURRENT Current is the rate of flow of charge.
Current is not used up, only energy
Current is measured in amps (amperes), A.
Current is measured with an ammeter, connected in series.
To connect in series you must break the circuit and put the ammeter acoss the gap, as shown in the diagram.
The symbol I is used for current in equations.
Why is the letter I used for current? ... please see FAQ.
Ammeter
in series

16. Measuring current flow
The brightness of a lamp is an indicator of the amount of current flowing through it. The brighter the lamp the more current flowing.
A better, and more accurate way of measuring current is to use an AMMETER A
Unit = AMPS (A)
symbol
A current measuring circuit:

17. Resistance
Resistance is anything in the circuit which slows the current flow down.
Resistors use up the energy supplied by the battery and turn it into other forms of energy for example
Light bulb – light and heat energy
Electric motor – kinetic and heat energy

18. VARIABLE RESISTOR
This is a component which can vary (change) the resistance of a circuit.
This relies on the fact that longer wires have more resistance, by changing the length you can control the current in a circuit
Remember to show circuit board with variable resistor as a dimmer switch.

19. Measuring RESISTANCE
Aim: To measure the resistance of various components.
A multimeter set to measure
Resistance in ohms (Ω) is used.
Simply connect the resistor accross]
The terminals and read the resistance.

20. Learning Check
What is electric current?
Explain potential difference?
What is resistance?
What are conductors and insulators?
How could you show if a substance is a conductor or an insulator?
What is a circuit?
Why must electric circuits be complete?
With what is (a) potential difference, (b) current (c) resistance measured with?
What are the units of (a) potential difference, (b) current (c) resistance

21. The ammeter and the voltmeter have to be connected with their + terminals towards the positive side of the battery.
Ohms Law
The potential difference is directly proportional to the current flowing in a conductor for a constant temperature.
V = constant (called the resistance R) or V = I x R I

23. 2323
Let's see how Ohm's law can be used to calculate the current, voltage or resistance in a circuit.
If we know the values of any two of the three quantities (voltage, current, and resistance) in this circuit, we can use Ohm's Law to determine the third.

24. calculate the amount of resistance (R) in a circuit, given values of voltage (E) and current (I):
2424

25. calculate the amount of voltage supplied by a battery, given values of current (I) and resistance (R):

28. Showing the Relationship between current and voltage – across a fixed resistor
Proving Ohm's Law
Set up this circuit and measure the current and voltage across the resistor at different values – measure at least 5 values
Voltage (V) Current (A) A V
Use 470 resistors

29. Relationship between current and voltage – across a fixed resistor
Now plot a graph of voltage against current for the fixed resistor circuit.
Given what we observed using the virtual physics laboratory when we changed the voltage or current what would you expect the graph to look like?
Voltage, V
Current, A

30. Series and Parallel Circuits
A. IN SERIES
The current flowing through a lamp makes it light. The more current the brighter the lamp.

31. Series and Parallel Circuits
A. IN PARALLEL
All lamps are normal brightness
All lamps have the same amount of current flowing through them.

32. SWITCHES
In a series circuit – one switch at either X or Y would control the lamps.
In a parallel circuit- Each lamp is controlled independently by each switch.

33. Effects of Electric Current.
Three effects of an electric current.
Remembering what has been done in the lesson to date and work we did in first year what effects of electric current have you noticed?
Heating effect. How would you show this?
Magnetic effect. How would you show this?
Chemical effect. How would you show this?

34. Heating effect of an Electric Current.
What would expect to happen the temperature?
Why?
What does it demonstrate?
Uses of the heating effect.
Kettle, oven, electric fire, fuse, immersion heater.

35. Magnetic effect of an electric current
What happens the compass when the switch is closed?
Why?
Can you think of any other way of demonstrating this effect of electricity?
Uses of the Magnetic effect
Electric motors, transformers, loudspeakers, computers.

36. Chemical effect of an electric current
Here electricity is being passed through water.
A chemical reaction takes place and splits water into hydrogen and oxygen.
This type of reaction is called Electrolysis and is an example of the chemical effect of electricity.
Uses of the chemical effect
Electrolysis -extracting and purifying metals.
Electroplating e.g silver plating

37. Keywords

38. Electricity in the Home
Mains supply two cables
Live (brown) at ±230 V
Neutral (blue) at 0 V
Main fuse on live coming into
house.
Both wires go through electricity meter recording the number of units used.
Both wires go through a distribution box with circuit breakers.

39. Circuit Breakers and Fuses
Circuit breakers and fuses cut off the current if it gets to high for safety, to prevent a fire etc.
Fuses melt if the current is too high (heating effect of an electric current)
Fuses come in various current ratings e.g 1A, 5A, 13A. Must be replaced if they blow.
Circuit breakers trip off if the current gets too high (magnetic effect of an electric current), can be switched back on when the fault is corrected.
Circuit breakers and fuses are always placed on the live wire (why?).

40. Plugs
Most appliances are connected to the electricity supply by pushing a plug into a wall socket.
Three wires
Live (brown) with fuse connected in it.
Neutral (blue)
Earth (green and yellow)
What are the safety features of a plug? (3)

41. Earthing
The Earth wire in your house is connected to a metal plate buried in the ground.
It is a safety device.
If the live wire get damaged and results in the metal body of an appliance such as an electric kettle becoming live then because it is earthed if you touch it the current flows to earth instead of through you.

42. Learning Check What is fuse? What effect of electricity does it show?
How does a fuse work?
What is circuit breaker? What effect of electricity does this show?
Why do we have an earth wire? How does it work?
What are the colours for live, neutral and earth wires?
What two advantages doe circuit breakers have over fuses?

43. The Cost of Electricity
Power = work done ÷ time measured in Watts (W)
The higher the power rating of an appliance the more energy it uses per second.
Rem. 1000W = 1 kW.
Examples.
1500 W heater uses 1500 J of energy per second .
2kW cooker uses 2000 J of energy per second.
How much energy does a 8.5 kW electric shower use?
8500 J /s

44. The Cost of Electricity
Unit of electricity sold by ESB = the kilowatt-hour kW h
(the joule is too small)
A kilowatt-hour is the electrical energy converted in other forms in 1 hour by a 1 kW appliance.
The number of kWh (units) = no. of kW x no. of hours
How many kWh are used by the following:
8 kW shower for 20 minutes.
1500 W iron for 1.5 hours.
100 W bulb for 20 hrs.
25 W i-pod for 40 hrs.

45. The Cost of Electricity
ANSWERS
The number of kWh (units) = no. of kW x no. of hours
Number of units = 8 kW x 0.33 hrs = 2.66
Number of units = 1.5 kW (1500W) x 1.5 hrs. = 2.25
Number of units = 0.1 kW (100W) x 20 hrs. = 2.0
Number of units = kW (25 W) x 40 hrs. = 1

46. The Cost of Electricity
The cost of the electricity
Cost = number of kWh (units) x price per unit (kWh)
Example
What is the cost of running a 3kW electric fire for 5 hours if the price per unit is 18 cent.?
ANSWER
Number of kWh = number of kW x number of hrs = 3 x 5=15
Cost = number of units x cost per unit
= x 18 cent
= 270 cent or €2.70

47. The Cost of Electricity
Example 2
Find the cost of using the following appliances if a unit of electricity costs 18 cent.
2000 W heater for 3 hrs.
1000 W iron for 10 mins.
150 W freezer for 24 hrs.
25 W light bulb for 40 hrs.
*** you must convert the W to kW first (how?)***
***then you must find the number of units (kWh)(how?)***

48. The Cost of Electricity
Answer
The number of kWh (units) = no. of kW x no. of hours
Number of units = 2 kW (2000 W) x 3 hrs. =
Number of units = 1 kW (1000W) x hrs. = 0.167
Number of units = 0.15 kW (150W) x 24 hrs. = 3.6
Number of units = kW (25W) x 40 hrs. = 1
Total number of units =
Cost = number of kWh (units) x price per unit (kWh)
Cost = x 18 cent
=194 cent or €1.94

49. The Cost of Electricity
Working out the cost of your electricity from the bill.
Example
The final reading electricity bill ón a 2 months ago is and the new reading is now the price per unit is 18 cent. The standing charge is € V.A.T is 13.5%. What is the cost of the electricity bill for 2 months?
Number of units used = new reading – previous reading
= – 21185
= 750

50. The Cost of Electricity
ANSWER (cont.)
Cost = number of kWh (units) x price per unit
= 750 x 18 cent
= €135.00
standing charge = €16.89 (now add the standing charge)
Total before VAT = € now calculate the V.A.T.
13.5% = €20.51
Total (including VAT)= €172.40

51. Electronics
Electronics is the branch of Physics dealing with the circuits using small carefully controlled currents to operate them.
Devices such as computers, iPods, CD players, mobile phones, digital cameras, detectors for smoke, heat, moisture, light and sound all operate by small carefully controlled currents in their circuits.
The Microchip made of silicon or germanium is at the heart of the electronic revolution containing millions of tiny components making up complex circuits to operate electronic devices.

53. Electronics (Diodes)
A diode is a device which allows current to pass in one direction only.
A diode has a silver band at one end which is called the cathode (-). the opposite end is called the anode (+).
Uses of diodes
Rectifiers – change a.c to d.c current.
Protect appliances the use d.c only from damage if connected the wrong way.

54. Electronics Forward biased
When a diode is connected with it cathode to the negative of the battery and anode to the positve of the battery it conducts electricity and is said to be forward biased.
The diode is connected such that current can flow, it is forward biased, so the lamp lights.

55. Electronics Reverse biased
When a diode is connected with it cathode to the positive of the battery and anode to the negative of the battery it does not conduct electricity and is said to be reverse biased.
The diode is connected such that current can't flow, it is reverse biased, so the lamp does not light.

56. Electronics Light Emitting Diodes (LED)
This a special diode that gives out light when current passes through them. The come in various colours, red, green, blue and yellow.
The shorter cathode lead is near the flat edge of the base.
The diagram shows the symbol for a LED.

57. Electronics Light Emitting Diodes (LED)
Like diodes the current flows in one direction only, forward biased.
Require only a very small current so must have a large resistor in series with them to protect them from damage.
Uses of LED's
Indicator lamps.
Digital displays on clocks, calculators etc.
Very reliable, long lasting, use little current so now used in traffic lights, bicycle lamps, torches.

58. Electronics
Use of LEDs to test the polarity of power supply or battery.
Depending on the polarity of the battery either the green or red LED will light.

59. Electronics The Light Dependent Resistor (LDR)
This is a variable resistor whose resistance depends ón the amount of light shining on it. In dim light the resistance is high and in bright light the resistance is low.
Uses of LDRs
Light controlled switches to switch on/off street lights automatically.
In light meters of cameras and burglar alarms.

60. Electronics Showing resistance of an LDR depends on brightness.
In the bright the the resistance is 500 Ω
In the darkness the resistance is 200 kΩ or 200,000 Ω

61. Learning Check What is a diode? Give two uses of diodes.
What is meant by reverse and forward bias?
What is a l.e.d.?
Give three uses of l.e.d.s.
What are the advantages of l.e.d.s over ordinary bulbs.
How does a LDR work.
How could you show how the resistance of an LDR changes with brightness?