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Intermediate 1 Physics

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  1. Intermediate 1 Physics Practical Electricity • Electrical Circuits • Resistance • Mains Electricity Beath High School - Int 1 Physics

  2. Intermediate 1 Physics Practical Electricity • Electrical Circuits Beath High School - Int 1 Physics

  3. Electrical Circuits A circuit will always have, • a source of e _ _ _ _ _ _ _ _ _ energy • an electrical comp _ _ _ _ t • wires forming a c _ _ _ _ _ _ _ path from one end of the source back to the other end. electrical onent complete Beath High School - Int 1 Physics

  4. Electrical Circuits complete If the circuit is c _ _ _ _ _ _ _ , there will be current. If the circuit is incomplete, there will be no c _ _ _ _ _ _ . current. Beath High School - Int 1 Physics

  5. Circuit Symbols Each electrical component has a symbol - called a "circuit symbol". When we draw circuit diagrams, we draw the circuit symbol instead of trying to draw the component itself. The following table is a list of the circuit symbols for all the electrical components needed for this course as well as a brief description of the function of the component. Beath High School - Int 1 Physics

  6. Circuit Symbols 1 Component Symbol Description supplies electrical energy Battery Converts electrical energy into light energy lamp Open: breaks a circuit Closed: completes a circuit switch Beath High School - Int 1 Physics

  7. Circuit Symbols 2 Component Symbol Description converts electrical energy into _ _ _ _ energy heater heat Opposes current; it converts electrical energy into heat resistor variable resistor A resistor whose resistance can be changed Beath High School - Int 1 Physics

  8. M A V Circuit Symbols 3 Component Symbol Description Converts electrical energy into kinetic energy Motor Used to measure electric current – always connected in series Ammeter Used to measure voltage – always connected in parallel Voltmeter Beath High School - Int 1 Physics

  9. W Circuit Symbols 4 Component Symbol Description Measures resistance directly – use when the component is not connected. Ohmmeter A protection device. It melts when the current gets too high. Fuse Beath High School - Int 1 Physics

  10. A Series Circuits When components are connected to allow only one path for the current, we say that the components are connected in series. three l _ _ _ _ in series lamps lamp, ammeter and fuse connected in series. Beath High School - Int 1 Physics

  11. A Series Circuits series If the components form a circuit, the circuit is called a s _ _ _ _ _ circuit. A series circuit. The battery, switch, lamp, variable resistor and ammeter are all connected in series. There is only o _ _ path for the c _ _ _ _ _ _ from one end of the battery, through each component in turn to the other end of the battery. one current Beath High School - Int 1 Physics

  12. Parallel Circuits more When components are connected to allow m _ _ _ than one path for the current, we say that the components are connected in parallel. parallel two lamps in p _ _ _ _ _ _ _ Beath High School - Int 1 Physics

  13. V Parallel Circuits lamp, heater and voltmeter connected in parallel. Beath High School - Int 1 Physics

  14. V Parallel Circuits battery A parallel circuit. The b _ _ _ _ _ _ , lamp and voltmeter are all connected in p _ _ _ _ _ _ _ . parallel. There is more than one separate path for the c _ _ _ _ _ _ . You can trace a separate path from the b _ _ _ _ _ _ through either component back to the o _ _ _ _ end of the battery. current battery other Beath High School - Int 1 Physics

  15. Measuring Current ammeter • Current is measured in amperes (a _ _ _ ). (The shorthand for amperes is ‘A’) • Current is measured using an a _ _ _ _ _ _ amps • To measure the current through a component, always connect the ammeter in s _ _ _ _ _ with the component. This means b _ _ _ _ _ _ _ the circuit to insert the ammeter. series breaking Beath High School - Int 1 Physics

  16. A Measuring Current Connecting an ammeter After Before The circuit is altered to include the ammeter in series with the lamp. The reading on the ammeter is the current t _ _ _ _ _ _ the lamp. through Beath High School - Int 1 Physics

  17. Measuring Voltage • Voltage is measured in v _ _ _ _ . • Voltage is measured using a voltmeter volts (Shorthand for volts is ‘V’) • To measure the voltage across a component, always connect the voltmeter in p _ _ _ _ _ _ _ with the component. parallel The voltmeter forms another parallel branch across the component. Beath High School - Int 1 Physics

  18. V Measuring Voltage Connecting the voltmeter Before After The voltmeter is added to make another branch in p _ _ _ _ _ _ _ with the lamp. parallel The reading on the voltmeter is the voltage across the l _ _ _ . lamp. Beath High School - Int 1 Physics

  19. A A Current and Voltage in Series Circuits identical The current through every component in a series circuit is i _ _ _ _ _ _ _ _ and is the same as the supply current. To measure the current in each lamp, connect an ammeter in s _ _ _ _ _ with each lamp. series Each ammeter will have the s _ _ _ reading. same Beath High School - Int 1 Physics

  20. Current and Voltage in Series Circuits The sum of the voltages across each component in a series circuit adds up to the supply voltage. The voltage across each lamp can be measured directly. Beath High School - Int 1 Physics

  21. V V V Current and Voltage in Series Circuits across This voltmeter measures the voltage a _ _ _ _ _ the battery. This is the supply voltage. To measure the voltage across each lamp, connect a voltmeter in parallel with each lamp. The voltmeter readings across the lamps a _ _ up to the supply voltage. add Beath High School - Int 1 Physics

  22. 6V A A 0.2A Examples 1. In the circuit shown, the current reading on one of the ammeters is 0.2 amperes. Find the current reading on the other ammeter and the current through each lamp. In a series circuit, the current is the s _ _ _ at all points. same The current reading on the other ammeter = A also the current through each lamp = A 0.2 0.2 Beath High School - Int 1 Physics

  23. V V V 1V 2V Examples 2. Find the supply voltage in the circuit shown below. In a series circuit, the voltages across each component add up to the supply voltage. The supply voltage = 2 + 1 = V 3 Beath High School - Int 1 Physics

  24. Current in parallel circuits The sum of the currents through each component in a parallel circuit adds up to the supply current. The current through each lamp and the battery can be measured directly. Beath High School - Int 1 Physics

  25. Current in parallel circuits To measure the current in each lamp, connect an ammeter in s _ _ _ _ _ with each lamp. series Beath High School - Int 1 Physics

  26. A A A Current in parallel circuits u r r e n t This ammeter measures the c _ _ _ _ _ _ through the battery. This is the supply current. To measure the current in each lamp, connect an ammeter in s _ _ _ _ _ with each lamp. series To measure the current through the battery, connect an a _ _ _ _ _ _ in series with the battery. ammeter The ammeter readings a _ _ up to the ammeter reading of the current through the supply. add Beath High School - Int 1 Physics

  27. Voltage in parallel circuits identical The voltage across every component in a parallel circuit is i _ _ _ _ _ _ _ _ and is the same as the supply voltage. The voltage across each lamp can be measured directly. Beath High School - Int 1 Physics

  28. V Voltage in parallel circuits voltmeter This v _ _ _ _ _ _ _ _ measures the voltage across the battery. This is the supply voltage. Beath High School - Int 1 Physics

  29. V V V Voltage in parallel circuits a r a l l e l To measure the voltage across each lamp, connect a voltmeter in p _ _ _ _ _ _ _ with each lamp. Each voltmeter will have the s _ _ _ reading. a m e The supply voltage is the s _ _ _ as the voltage across each lamp. a m e Beath High School - Int 1 Physics

  30. Intermediate 1 Physics Practical Electricity • Resistance Beath High School - Int 1 Physics

  31. Resistance Materials oppose current and some materials oppose it more than others. The opposition to current is called r _ _ _ _ _ _ _ _ _ . e s i s t a n c e An increase in resistance causes a d _ _ _ _ _ _ _ in current. e c r e a s e Beath High School - Int 1 Physics

  32. Resistance A resistor causes electrical energy to be converted into h _ _ _ energy in the material. Sometimes this is a nuisance – when circuits heat up and get too h _ _ . Sometimes it is useful – when heat is required, for example in k e t _ _ _ _ or cookers. e a t o t t l e s Beath High School - Int 1 Physics

  33. W Measuring Resistance h m s (Shorthand for ohms is “W” – the Greek letter omega) • Resistance is measured in o _ _ _ . • Resistance can be measured using an o _ _ _ _ _ _ _ . h m m e t e r To measure resistance, connect the ohmmeter directly across the resistor or component whose resistance you want to measure (nothing else connected). Beath High School - Int 1 Physics

  34. A Calculating resistance from ammeter and voltmeter values Measure the current through the resistor by connecting an a _ _ _ _ _ _ in s _ _ _ _ _ . Put the resistor or component into a circuit. m m e t e r e r i e s Beath High School - Int 1 Physics

  35. A V Calculating resistance from ammeter and voltmeter values Measure the voltage across the resistor, connecting a v _ _ _ _ _ _ _ _ in parallel. Put the resistor or component into a circuit. o l t m e t e r Beath High School - Int 1 Physics

  36. voltage resistance = current A V Calculating resistance from ammeter and voltmeter values Calculate resistance using: Beath High School - Int 1 Physics

  37. voltage resistance = current A voltage 12 = current 0.1 V Calculating resistance from ammeter and voltmeter values Calculate resistance using: Example: The current through a resistor is 0.1 amperes when the voltage across it is 12 volts. Calculate the resistance. resistance = = 120W Beath High School - Int 1 Physics

  38. Variable resistors It is often useful to be able to adjust the flow of current continuously. For example; controlling the loudness or brightness of a TV, the heat setting on a toaster, adjusting the speed of a model train. To do this we use a v _ _ _ _ _ _ _ resistor; symbol: a r i a b l e When the resistance is reduced, the current i _ _ _ _ _ _ _ _. n c r e a s e s Beath High School - Int 1 Physics

  39. Intermediate 1 Physics Practical Electricity • Mains Electricity Beath High School - Int 1 Physics

  40. MAINS ELECTRICITY Safety Note: Mains electricity is dangerous. Never experiment with mains electricity. Electricity supplied to houses is called m _ _ _ _ electricity. a i n s Mains electricity is dangerous because your body can c _ _ _ _ _ electricity and mains voltage can cause a current large enough to k _ _ _ you. o n d u c t i l l Your body conducts even m _ _ _ if it is wet or damp, this is the reason why there must be no sockets or switches in a _ _ _ _ room. o r e b a t h Beath High School - Int 1 Physics

  41. MAINS ELECTRICITY The declared value of mains voltage is _ _ _ volts 2 3 0 All mains a _ _ _ _ _ _ _ _ _ in Britain are designed to operate with a voltage of 230 volts across them. p p l i a n c e s This means that the household wiring must be such that all the appliances are connected in p _ _ _ _ _ _ _ . a r a l l e l This ensures that each appliance receives the same voltage (230V). Beath High School - Int 1 Physics

  42. The three pin plug Household wiring consists of cables in which there are t _ _ _ _ wires. h r e e The cable is connected to the m _ _ _ _ using a three pin plug – one pin for each of the wires. a i n s Beath High School - Int 1 Physics

  43. The three pin plug r o w n The live wire is the wire connected to the 230 volts supply from the p _ _ _ _ station. It is coloured b _ _ _ _ . If you touch the brown wire of an appliance which is connected to the mains you will get a s _ _ _ _ which can kill you. The switch in an appliance is always connected to the l _ _ _ wire so that when the switch is off, the appliance is dis _ _ _ _ _ _ _ _ _ from the 230 V supply from the mains. 1. The live wire (b _ _ _ _ ) o w e r r o w n h o c k i v e c o n n ec te d Beath High School - Int 1 Physics

  44. The three pin plug l u e The neutral wire is used to complete the circuit from the appliance to the mains. If you touch the blue wire in an appliance you can still get a shock if the appliance is connected to the m _ _ _ _ and working. 2. The neutral wire (b _ _ _ ) a i n s Beath High School - Int 1 Physics

  45. The three pin plug e l l o w r e e n The earth wire does not normally carry c _ _ _ _ _ _ . It is a s _ _ _ _ _ device. It only carries current if there is a f _ _ _ _ in the appliance. All appliances with metal parts which can be touched must have an e _ _ _ _ wire. u r r e n t 3. The earth wire (g _ _ _ _ and y _ _ _ _ _ ) a f e t y a u l t a r t h Beath High School - Int 1 Physics

  46. Double Insulated appliances Appliances are called "double insulated" if it is impossible to touch the l _ _ _ wire inside it. These appliances do not need an e _ _ _ _ wire and only have a live and neutral wire. Double insulated appliances have this symbol on them. i v e a r t h Double insulated symbol. Appliances with this symbol do not have an earth wire since it is impossible to touch any m _ _ _ _ parts. e t a l Beath High School - Int 1 Physics

  47. cable grip Wiring a plug All appliances are connected to the mains power supply by a three pin p _ _ _ . The plug which connects an appliance to the mains must be connected as shown: l u g e a r t h y e l l o w b r o w n u s e b l u e l i v e n e u t r a l Beath High School - Int 1 Physics

  48. e a r t h y e l l o w b r o w n u s e b l u e cable grip l i v e n e u t r a l Wiring a plug a n g e r It is d _ _ _ _ _ ous to operate an appliance if the wires are not connected as shown here. If you are unsure about a plug’s wiring, do not use it! Beath High School - Int 1 Physics

  49. The fuse The fuse in a plug is a s _ _ _ _ _ device to protect the c _ _ _ _ . It melts if the current in the cable gets too h _ _ _ . All plugs contain a fuse. The fuse is always connected between the l _ _ _ pin of the plug and thel _ _ _ wire of the appliance. This is so that if something goes wrong, the fusem _ _ _ _ and disconnects the live wire of the appliance from the m _ _ _ _ power supply. afety able igh ive ive elts ains Beath High School - Int 1 Physics

  50. power current = voltage Fuse values Fuse values are usually 3 a _ _ _ _ _ or 13 a _ _ _ _ _ in domestic appliances. It is important to use the correct fuse values to avoid too high a c _ _ _ _ _ _. The fuse value can be calculated from the v _ _ _ _ _ _ and the p _ _ _ _ rating: mpere mpere urrent oltage ower Beath High School - Int 1 Physics