1. 25/08/2015 P6 Electricity for Gadgets AGAC

2. 25/08/2015 Circuit Symbols VA Battery Power Supply Capacitor Resistor LDR Voltmeter Ammeter Variable resistor Diode Switch Bulb Thermistor

3. Equations for this unit (Foundation) 25/08/2015

4. Equations For This Unit (Higher)

5. 25/08/2015 Basic ideas… Electric current is when electrons start to flow around a circuit. We use an _________ to measure it and it is measured in ____. Potential difference (also called _______) is how big the push on the electrons is. We use a ________ to measure it and it is measured in ______, a unit named after Volta. Resistance is anything that resists an electric current. It is measured in _____. Words: volts, amps, ohms, voltage, ammeter, voltmeter ammeter amps voltage voltmeter volts ohms

6. 25/08/2015 More basic ideas… If a battery is added the current will ________ because there is a greater _____ on the electrons so they move ______ If a bulb is added the current will _______ because there is greater ________ in the circuit, so the electrons move _____ Words – faster, decrease, slower, increase, push, resistance increase push faster decrease resistance slower

7. 25/08/2015 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 I is used for current because current was originally referred to as “electrical intensity”.

8. 25/08/2015 An example question: V A 1)What is the resistance across this bulb? R = V = 10 = 5  I 2 1)Assuming all the bulbs are the same what is the total resistance in this circuit? 5 x 3 = 15  Voltmeter reads 10V Ammeter reads 2A

9. 25/08/2015 More examples… 12V 3A 6V 4V 2A 1A 2V What is the resistance of these bulbs? 4 4  2 2  2 2  Difficult!! Difficult!

10. 25/08/2015Resistance Resistance is anything that opposes an electric current. Resistance (Ohms,  ) = Potential Difference (volts, V) Current (amps, A) What is the resistance of the following: 1)A bulb with a voltage of 3V and a current of 1A. 2)A resistor with a voltage of 12V and a current of 3A 3)A diode with a voltage of 240V and a current of 40A 4)A thermistor with a current of 0.5A and a voltage of 10V 3 3  4 4  6 6  20 

11. 25/08/2015 F

12. Current-Voltage graphs for conductors 1) An Ohmic conductor2) A non-Ohmic conductor High resistance Low resistance V I V I In Ohmic conductors the resistance of the conductor stays the same. In non-Ohmic conductors (like filament bulbs) the resistance of the conductor increases as the current increases (when it gets hot).

13. 25/08/2015 LDRs and Thermistors 2) Thermistor – resistance DECREASES when temperature INCREASES 1) Light dependant resistor – resistance DECREASES when light intensity INCREASES Resistance Amount of light Resistance Temperature

14. 25/08/2015 F d Divides a value of voltage (1) by the corresponding value of current(1)

15. 25/08/2015 Divides a value of voltage (1) by the corresponding value of current(1)

16. 25/08/2015 F LDR thermistor capacitor diode

17. 25/08/2015 Potential Dividers 0V V IN V OUT 0V R1R1 R2R2 (R 1 + R 2 ) V IN x (R 2 ) V OUT The Potential Divider equation:

18. 25/08/2015 Find the output voltage (Vout)1 0V V IN V OUT 0V R1 R1  R2 R2  50V V OUT 0V 100  (R 1 + R 2 ) V IN x (R 2 ) V OUT 25V Q1 Example

19. 25/08/2015 Find the output voltage (Vout)2 0V V IN V OUT 0V R1 R1  R2 R2  3V V OUT 0V 200  100  (R 1 + R 2 ) V IN x (R 2 ) V OUT 1V Q2 Example

20. 25/08/2015 Find the output voltage (Vout)3 0V V IN V OUT 0V R1 R1  R2 R2  12V V OUT 0V 5  15  (R 1 + R 2 ) V IN x (R 2 ) V OUT 9V Q3 Example

21. 25/08/2015 Practical applications 0V V in V OUT Here’s a potential divider that is used to control light-activated switches… When the light intensity on the LDR decreases its resistance will ________. This causes V OUT to _______ so the processor and output will probably turn _____. The variable resistor can be adjusted to change the ________ of the whole device. Words – decrease, sensitivity, increase, off increase decrease off sensitivity

22. 25/08/2015 (2) input 0V output

23. 25/08/2015 Comparing magnets and solenoids N S Magnet: Solenoid:

24. 25/08/2015 Magnetic Field around a current- carrying wire “Right hand corkscrew” or “right hand grip” rule The X is like looking at a dart moving away from you i.e. into the page. This is the direction of the current in the wire. This produces a clockwise magnetic field The dot is like looking at a dart coming towards you i.e. Out of the page. This is the direction of the current in the wire. This produces an anticlockwise magnetic field

25. 25/08/2015 Magnetic field around a rectangular coil This looks like the solenoid seen on a previous slide

26. 25/08/2015 Revision of DC and AC DC stands for “Direct Current” – the current only flows in one direction: AC stands for “Alternating Current” – the current changes direction 50 times every second (frequency = 50Hz) 1/50 th s 230V V V Time T

27. 25/08/2015 The Motor Effect S N 1)What will happen to this wire? 2)How can you make it move faster? 3)How can you make it move in a different direction? move away stronger magnetic field more currentadd battery/ reverse currentORreverse magnet

28. 25/08/2015 Current-carrying wire in a magnetic field S N F = Force B = Magnetic field I = Current Q. Where will this wire go? Field goes from N to S Current is coming upwards towards you

29. 25/08/2015 Current-carrying wire in a magnetic field S N F = Force B = Magnetic field I = Current Q. Where will this wire go?

30. 25/08/2015 downwards

31. 25/08/2015 Electric Motors

32. 25/08/2015 F 3

33. Electromagnetic Induction N The direction of the induced current is reversed if… 1)The wire is moved in the opposite direction 2)The field is reversed The size of the induced current can be increased by: 1)Increasing the speed of movement 2)Increasing the magnet strength

34. 25/08/2015 Electromagnetic induction The direction of the induced current is reversed if… 1)The magnet is moved in the opposite direction 2)The other pole is inserted first The size of the induced current can be increased by: 1)Increasing the speed of movement 2)Increasing the magnet strength 3)Increasing the number of turns on the coil

35. 25/08/2015 DC Generators Basically, a DC generator is an electric motor in reverse: 1) Remove the battery 2) Turn the coil manually instead. A DC current will be generated in the wires

36. 25/08/2015 AC Generators Magnetic Field Slip rings and brushes

37. 25/08/2015 AC Generators SN Voltage Time

38. 25/08/2015 Questions on the AC Generator 1)How does the generator work? 2)How would you increase its output? Give two answers 3)How would you increase the frequency? Electromagnetic induction More coils Stronger magnet Turn it faster

39. 25/08/2015 F increases stays the same

40. 25/08/2015 increases stays the same

41. 25/08/2015 Move magnet away from coil or move coil away from magnet

42. 25/08/2015Transformers Time Current through primary Magnetic field Voltage induced in secondary

43. Transformers Look back at the previous slide. The 2 points to realise are 1 You only get a voltage if the magnetic field is CHANGING 2 You get a greater voltage if the magnetic field is changing more quickly. 25/08/2015

44. Transformers Transformers are used to _____ __ or step down _______. They only work on AC because an ________ current in the primary coil causes a constantly alternating _______ ______. This will “_____” an alternating current in the secondary coil. Words – alternating, magnetic field, induce, step up, voltage We can work out how much a transformer will step up or step down a voltage: Voltage across primary (V p ) No. of turns on secondary (N s )Voltage across secondary (V s ) No. of turns on primary (N p ) …and the current changes using this formula: V P I P = V S I S step up voltage alternating magnetic field induce

45. 25/08/2015 Some example questions Primary voltage V p Secondary voltage V s No. of turns on primary N p No. of turns on secondary N s Step up or step down? 6V24V100?? 400V200V?1000? 250V?20020? ?230V1501500? 1)A transformer increases voltage from 10V to 30V. What is the ratio of the number of turns on the primary coil to the number of turns on the secondary coil? 2)A current of 0.5A is supplied to a transformer that steps down a voltage from 230V to 23V. What is the current from the secondary coil? 400 Step up Step down Step up 2000 25V 23 1:3 5A

46. 25/08/2015 Transformers in the National Grid Electricity reaches our homes from power stations through the National Grid: If electricity companies transmitted electricity at 230 volts through overhead power lines there would be too much ______ loss by the time electricity reaches our homes. This is because the current is ___. To overcome this they use devices called transformers to “step up” the voltage onto the power lines. They then “____ ____” the voltage at the end of the power lines before it reaches our homes. This way the voltage is _____ and the current and power loss are both ____. Words – step down, high, power, low, high Power station Step up transformer Step down transformer Homes power high step down highlow

47. 25/08/2015 F No output/zero step-down phone-chargers radio laptopslow voltage lighting Any from: V out 240 = 200 4000 V out =12

48. 25/08/2015 V out 240 = 200 4000 V out = 12 An output voltage is induced in the secondary coil when a changing magnetic field passes through the coil The changing magnetic field is produced by the primary coil DC produces a steady field AC produces a changing field Any three from:

49. 25/08/2015 Isolating Transformers Words – electrocuted, shaver, voltage, contact, coils, number An isolating transformer is used in some mains circuits (for example, a bathroom _____ socket). Isolating transformers do not change the _____; they simply consist of two ____ which have the same _______ of turns that don’t make _____ with each other. This stops the user from getting ___________ from the mains supply. shaver voltagecoils contact electrocuted number

50. 25/08/2015Diodes I V A diode is a device that only allows current to flow in one direction: If alternating current is passed through a diode it becomes “half-wave rectified”: V T V T The current flows easily in the forwards direction but there is very high resistance to the reverse current.

51. 25/08/2015 Full-Wave Rectification 1 A group of 4 diodes can be used to make a “bridge rectifier” circuit to make full-wave rectification: AC supply Load V T V T

52. Full Wave Rectification 2 25/08/2015 AC supply Load AC supply Load + - - + The current can only flow through the diode in the direction of the arrow Current flows from positive to negative First half of the a.c. wave Second half of the a.c. wave Notice that the current flows the same way through the load resistor i.e. DC

53. 25/08/2015 The Capacitor A capacitor is a device that can store charge (it has a “capacity”). Here’s how they work: e

54. 25/08/2015 Charging and discharging a capacitor P.d. across capacitor Time Current in circuit Time P.d. across capacitor Time Current in circuit

55. 25/08/2015Smoothing Capacitors can be used in “smoothing” circuits to “smooth” out a supply: AC supply Input Output without capacitor Output with capacitor

56. 25/08/2015 Logic Gates Logic gates are the basics behind any kind of processor. There are 5 that you need to know for GCSE: NOT gate: AND gate: OR gate:

57. 25/08/2015 Logic Gates NAND gate: NOR gate:

58. 25/08/2015 Logic gates NOT gate – “the output is NOT what the input is” AND – “the output is on if A AND B are both on” OR – “the output is on if A OR B are on” InputOutput 01 10 Input AInput BOutput 000 010 100 111 Input AInput BOutput 000 011 101 111

59. 25/08/2015 Logic gates NAND – “an AND gate and a NOT gate in series” Input AInput BOutput 001 011 101 110 TIP: You don’t need to learn this separately. Just learn the AND gate and this gate just has the opposite outputs

60. 25/08/2015 Logic gates NOR – “a NOR gate and a NOT gate in series” Input AInput BOutput 001 010 100 110 TIP: You don’t need to learn this separately. Just learn the OR gate and this gate just has the opposite outputs

61. 25/08/2015 Some problems to solve The pump on a central heating system is switched on at room temperature if the system is switched on (with the slide switch). When the temperature rises the pump needs to be switched off. Design a circuit that will sound a buzzer if the temperature of a hot radiator falls during the day ONLY. Include a test switch to check the operation of the buzzer. Design a circuit for a gardener that will warn them of cold conditions at night. The alarm should be able to be switched off.

62. 25/08/2015 Using LDRs and Thermistors as inputs Thermistors and LDRs can be used as the input to a logic gate: When the light intensity on the LDR decreases its resistance will ________. This causes the input to the ____ gate to turn ___ so the output will turn on. The variable resistor can be adjusted to change the ________ of the whole device. Words – AND, sensitivity, increase, on 5V 6V Output

63. 25/08/2015 Complex Logic Gate problems Work out the truth tables for the following arrangements: A B J O ABJO 00110011 01010101 1 1 0 0 1 1 0 1 J depends on A O depends On B and J

64. 25/08/2015 Complex Logic Gate problems Work out the truth tables for the following arrangements: A B J O ABJO 00110011 01010101 11001100 11011101

65. 25/08/2015 Complex Logic Gate problems Work out the truth tables for the following arrangements: A B C J KO ABCJKO 0000111100001111 0011001100110011 0101010101010101 J depends on A and B K depends on C and J 0 0 0 0 0 0 1 1 0 1 0 1 0 1 1 1

66. 25/08/2015 Complex Logic Gate problems Work out the truth tables for the following arrangements: A B C J KO ABCJKO 0000111100001111 0011001100110011 0101010101010101 0000001100000011 0101011101010111 1010100010101000

67. 25/08/2015 Complex Logic Gate problems Work out the truth tables for the following arrangements: ABCDJKLO 00000000111111110000000011111111 00001111000011110000111100001111 00110011001100110011001100110011 01010101010101010101010101010101 A B C D J KL O

68. 25/08/2015 Complex Logic Gate problems Work out the truth tables for the following arrangements: ABCDJKLO 00000000111111110000000011111111 00001111000011110000111100001111 00110011001100110011001100110011 01010101010101010101010101010101 00000000000011110000000000001111 01110111011101110111011101110111 10001000100010001000100010001000 00000000000010000000000000001000 A B C D J KL O

69. 25/08/2015Relays Circuits such as those containing logic gates only take very ______ currents. These circuits may be needed to operate a device that takes a much _____ current, e.g. a _________. To do this the circuit would need a RELAY switch, a device made of an ____________ that can operate a switch. A relay switch is activated by the small current and the switch part is placed in the circuit needing a large current: Symbol for relay: Words – motor, larger, electromagnet, small M small larger motor electromagnet

70. 25/08/2015 Latch Circuits A Latch is a switch that stays on after is has been switched on (a burglar alarm, for example). Bistable Latch circuits can be made using NOR gates: Bistable latch circuits work by: 1)A brief “on” signal at one ____ results in a permanent “___” signal at the latch ______ 2)A brief “on” signal at the other input causes an “___” signal at the latch output 3)An “off” signal at both inputs leaves the latch signal _________. Words – on, off, unchanged, output, input input on output off unchanged

71. 25/08/2015 F low high once the alarm starts it stays on (1) even if the door is shut or it is reset s

72. 25/08/2015 0 0 0 1 fan needs a large current logic gate only produces a small current relay can use low inputto switch large fan current Any two from:

73. 25/08/2015 decreases Input increases Goes to 1/high/on or Allows the temperature at which the fan comes on to be adjusted