* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download General
Mercury-arc valve wikipedia , lookup
Ground loop (electricity) wikipedia , lookup
Flexible electronics wikipedia , lookup
Electrification wikipedia , lookup
History of electromagnetic theory wikipedia , lookup
Three-phase electric power wikipedia , lookup
Power engineering wikipedia , lookup
Portable appliance testing wikipedia , lookup
Electrical substation wikipedia , lookup
Ground (electricity) wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
History of electric power transmission wikipedia , lookup
Current source wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Buck converter wikipedia , lookup
Voltage optimisation wikipedia , lookup
Opto-isolator wikipedia , lookup
Stray voltage wikipedia , lookup
Electrical ballast wikipedia , lookup
Earthing system wikipedia , lookup
Network analysis (electrical circuits) wikipedia , lookup
Surge protector wikipedia , lookup
Alternating current wikipedia , lookup
Intermediate 1 Physics Practical Electricity Electrical Circuits Resistance Mains Electricity Beath High School - Int 1 Physics 1 Intermediate 1 Physics Practical Electricity Electrical Circuits Beath High School - Int 1 Physics 2 Electrical Circuits A circuit will always have, a source of e _ _ electrical _ _ _ _ _ _ _ energy an electrical comp onent _ _ _ _ t wires forming a c _ complete _ _ _ _ _ _ path from one end of the source back to the other end. Beath High School - Int 1 Physics 3 Electrical Circuits If the circuit is ccomplete _ _ _ _ _ _ _ , there will be current. If the circuit is incomplete, there will be no current. c______. Beath High School - Int 1 Physics 4 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 5 Circuit Symbols 1 Component Battery lamp switch Symbol Description supplies electrical energy Converts electrical energy into light energy Open: breaks a circuit Closed: completes a circuit Beath High School - Int 1 Physics 6 Circuit Symbols 2 Component heater Symbol Description converts electrical energy into _ heat _ _ _ energy resistor Opposes current; it converts electrical energy into heat variable resistor A resistor whose resistance can be changed Beath High School - Int 1 Physics 7 Circuit Symbols 3 Component Motor Ammeter Voltmeter Symbol Description M Converts electrical energy into kinetic energy A Used to measure electric current – always connected in series V Used to measure voltage – always connected in parallel Beath High School - Int 1 Physics 8 Circuit Symbols 4 Component Ohmmeter Fuse Symbol W Description Measures resistance directly – use when the component is not connected. A protection device. It melts when the current gets too high. Beath High School - Int 1 Physics 9 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 _lamps _ _ _ in series A lamp, ammeter and fuse connected in series. Beath High School - Int 1 Physics 10 Series Circuits If the components form a circuit, the circuit is called a s _series _ _ _ _ circuit. A A series circuit. The battery, switch, lamp, variable resistor and ammeter are all connected in series. There is only oone _ _ path for the c _current _ _ _ _ _ from one end of the battery, through each component in turn to the other end of the battery. Beath High School - Int 1 Physics 11 Parallel Circuits When components are connected to allow mmore _ _ _ than one path for the current, we say that the components are connected in parallel. two lamps in pparallel _______ Beath High School - Int 1 Physics 12 Parallel Circuits lamp, heater and voltmeter connected in parallel. V Beath High School - Int 1 Physics 13 Parallel Circuits A parallel circuit. The b _battery _ _ _ _ _ , lamp and voltmeter are all connected in pparallel. _______. There is more than one separate path for the c _current _ _ _ _ _ . You can trace a V separate path from the battery b______ through either component back to the oother _ _ _ _ end of the battery. Beath High School - Int 1 Physics 14 Measuring Current Current is measured using an ammeter a______ Current is measured in amperes (aamps _ _ _ ). (The shorthand for amperes is ‘A’) To measure the current through a component, always connect the ammeter in s _series _ _ _ _ with the component. This means b _breaking _ _ _ _ _ _ the circuit to insert the ammeter. Beath High School - Int 1 Physics 15 Measuring Current Connecting an ammeter A Before After The circuit is altered to include the ammeter in series with the lamp. The reading on the ammeter is the current t _through _ _ _ _ _ the lamp. Beath High School - Int 1 Physics 16 Measuring Voltage Voltage is measured using a voltmeter Voltage is measured in vvolts ____. (Shorthand for volts is ‘V’) To measure the voltage across a component, always connect the voltmeter in p _ _parallel _ _ _ _ _ with the component. The voltmeter forms another parallel branch across the component. Beath High School - Int 1 Physics 17 Measuring Voltage Connecting the voltmeter Before After V The voltmeter is added to make another branch in parallel p_______ with the lamp. The reading on the voltmeter is the voltage across the lamp. l___. Beath High School - Int 1 Physics 18 Current and Voltage in Series Circuits The current through every component in a series circuit is i _ _identical _ _ _ _ _ _ and is the same as the supply current. A A To measure the current in each lamp, connect an ammeter in s _series _ _ _ _ with each lamp. Each ammeter will have the ssame _ _ _ reading. Beath High School - Int 1 Physics 19 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 20 Current and Voltage in Series Circuits This voltmeter measures the voltage a _across _ _ _ _ the battery. This is the supply voltage. V V V To measure the voltage across each lamp, connect a voltmeter in parallel with each lamp. The voltmeter readings across the lamps aadd _ _ up to the supply voltage. Beath High School - Int 1 Physics 21 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. 6V A A 0.2A In a series circuit, the current is the ssame _ _ _ at all points. The current reading on the other ammeter = 0.2 A also the current through each lamp = 0.2 A Beath High School - Int 1 Physics 22 Examples 2. Find the supply voltage in the circuit shown below. V V V 1V 2V In a series circuit, the voltages across each component add up to the supply voltage. The supply voltage = 2 + 1 =3 V Beath High School - Int 1 Physics 23 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 24 Current in parallel circuits To measure the current in each lamp, connect an ammeter in s _series _ _ _ _ with each lamp. Beath High School - Int 1 Physics 25 Current in parallel circuits u _r _ r e_ _n _ t through the This ammeter measures the c _ battery. This is the supply current. A A A To measure the current in each lamp, connect an ammeter in s _series _ _ _ _ with each lamp. To measure the current through the battery, connect an a _ammeter _ _ _ _ _ in series with the battery. The ammeter readings aadd _ _ up to the ammeter reading of the current through the supply. Beath High School - Int 1 Physics 26 Voltage in parallel circuits The voltage across every component in a parallel circuit is i _ _identical _ _ _ _ _ _ and is the same as the supply voltage. The voltage across each lamp can be measured directly. Beath High School - Int 1 Physics 27 Voltage in parallel circuits This v _ voltmeter _ _ _ _ _ _ _ measures the voltage across the battery. V This is the supply voltage. Beath High School - Int 1 Physics 28 Voltage in parallel circuits To measure the voltage across each lamp, connect a r _a _ l _ l e voltmeter in p a_ _ _ _l with each lamp. V V Each voltmeter will have the s a_ m __ e reading. The supply voltage is the s a_ m __ e as the voltage across each lamp. Beath High School - Int 1 Physics V 29 Intermediate 1 Physics Practical Electricity Resistance Beath High School - Int 1 Physics 30 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. e _c _ re s e_ in An increase in resistance causes a d _ _ a_ _ current. Beath High School - Int 1 Physics 31 Resistance A resistor causes electrical energy to be converted into h _ e_ a t_ energy in the material. Sometimes this is a nuisance – when circuits heat up and get too h _ o t_ . Sometimes it is useful – when heat is required, for example in k e t _ t _l _ e_ s or cookers. Beath High School - Int 1 Physics 32 Measuring Resistance Resistance is measured in o _ h_ m _s . (Shorthand for ohms is “W” – the Greek letter omega) h_ m _m_e _t _ e_ r . Resistance can be measured using an o _ To measure resistance, connect the ohmmeter directly across the resistor or component whose resistance you want to measure (nothing else connected). W Beath High School - Int 1 Physics 33 Calculating resistance from ammeter and voltmeter values Put the resistor or component into a circuit. Measure the current through the resistor by m _m_e_t _ e_ r in s _ connecting an a _ e _r _ i _ e s_ . A Beath High School - Int 1 Physics 34 Calculating resistance from ammeter and voltmeter values Put the resistor or component into a circuit. Measure the voltage across the resistor, connecting a tm e_ t e_ _ r in parallel. v o_ _l _ __ A V Beath High School - Int 1 Physics 35 Calculating resistance from ammeter and voltmeter values Calculate resistance using: resistance = voltage current A V Beath High School - Int 1 Physics 36 Calculating resistance from ammeter and voltmeter values Calculate resistance using: resistance = Example: voltage current The current through a resistor is 0.1 amperes when the voltage across it is 12 volts. Calculate the resistance. A resistance = voltage 12 = = 120W current 0.1 V Beath High School - Int 1 Physics 37 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 _ _ _l e_ resistor; symbol: a _r _i _ ab When the resistance is reduced, the current i n_ _c _ r e_ _ a_ s _e _. s Beath High School - Int 1 Physics 38 Intermediate 1 Physics Practical Electricity Mains Electricity Beath High School - Int 1 Physics 39 MAINS ELECTRICITY Safety Note: Mains electricity is dangerous. Never experiment with mains electricity. Electricity supplied to houses is called m a_ _i _ n_ s electricity. Mains electricity is dangerous because your body can co _ n_ d_ u_c_t electricity and mains voltage can cause a current large enough to k _i _l _ l you. r e_ if it is wet or damp, Your body conducts even m _o _ this is the reason why there must be no sockets or b_ a_ th switches in a _ _ room. Beath High School - Int 1 Physics 40 MAINS ELECTRICITY The declared value of mains voltage is _ _0 _ volts 23 p _p _l _ i _ a n_ _c _ e s_ in Britain are designed All mains a _ to operate with a voltage of 230 volts across them. 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 41 The three pin plug Household wiring consists of cables in which there are h_ r e_ e_ wires. t_ a _i _n _ s using a three The cable is connected to the m _ pin plug – one pin for each of the wires. Beath High School - Int 1 Physics 42 The three pin plug 1.The live wire (b _r o_ w_ n_ ) The live wire is the wire connected to the 230 volts supply from the p _ __ ow e r_ station. It is coloured b_ _ n_ . If you touch the brown wire of an appliance r o_ w which is connected to the mains you will get a s _ h_ o c_ k_ which can kill you. The switch in an appliance is always connected to the l _i v_e_ wire so that when the switch c o_ _ n_ n e_ c_ t_ e_ d_ from is off, the appliance is dis _ the 230 V supply from the mains. Beath High School - Int 1 Physics 43 The three pin plug 2.The neutral wire (b _ 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 i _ n s_ and working. connected to the m a_ _ Beath High School - Int 1 Physics 44 The three pin plug e _ l l_ o_ w_ ) 3.The earth wire (g _ _ and y _ r _ e _e n The earth wire does not normally carry c u _ _r _ r e_ _ n_ t . It is a s a_ _f _ e t_ _ y device. It only carries current if there is a f a_ u_ _ l t_ in the appliance. All appliances with metal parts which can be touched must have an e a_ _r t_ h_ wire. Beath High School - Int 1 Physics 45 Double Insulated appliances Appliances are called "double insulated" if it is impossible i _ v e_ wire inside it. These appliances do to touch the l _ t h_ wire and only have a live and not need an e a _ _r _ neutral wire. Double insulated appliances have this symbol on them. Double insulated symbol. Appliances with this symbol do not have an earth wire since it is impossible to touch any a _l parts. me _ _t _ Beath High School - Int 1 Physics 46 Wiring a plug All appliances are connected to the mains power supply by l _ u g_ . a three pin p _ The plug which connects an appliance to the mains must be connected as shown: e_ a_ _r _t _h pin Earth wire l l_ o_ w_ ) (Green/ y _ e _ _ Live wire r _o w n) (b _ _ _ _ s _e Fu _ _ Neutral wire l u_ e_ ) (b _ _ cable grip n_ e u _t _r _a _l _ _ pin l i_ v_ e_ _ pin Beath High School - Int 1 Physics 47 Wiring a plug n_ g _e _r ous to operate an appliance if the wires It is d a_ _ are not connected as shown here. If you are unsure about a plug’s wiring, do not use it! Earth wire l l_ o_ w_ ) (Green/ y _ e _ _ e_ a_ _r _t _h pin Live wire r _o w n) (b _ _ _ _ s _e Fu _ _ Neutral wire l u_ e_ ) (b _ _ cable grip n_ e u _t _r _a _l _ _ pin l i_ v_ e_ _ pin Beath High School - Int 1 Physics 48 The fuse The fuse in a plug is a s a_ f_ e __ _ device to protect t y the c a __ b_ l e_ . It melts if the current in the cable i g_ h_ . All plugs contain a fuse. gets too h _ i v_ e_ pin The fuse is always connected between the l _ i v_ e_ wire of the appliance. This of the plug and the l _ is so that if something goes wrong, the fuse m _ e_ l t_ s_ and disconnects the live wire of the appliance from the m_ a_ i n_ s_ power supply. Beath High School - Int 1 Physics 49 Fuse values Fuse values are usually 3 a m __ __ p _e _r _e in p_ e _r _e or 13 a m domestic appliances. It is important to use the correct fuse values to avoid too high a c _ u_ r_ r_ e_ n _. t The fuse value can be calculated from the v _ __ o_ l t_ a_ g_ e_ and the p o_ w e _r rating: current = power voltage Beath High School - Int 1 Physics 50 Fuse values Example: Calculate the fuse value required for a mains appliance with a power of 1150 watts. current = power voltage = 1150 230 = 5A 13 Therefore a ______ ampere fuse is required. As a general rule if the power rating is 700 W or more, a 13 ampere (13 A) fuse must be used. If the power rating is 700 W a 3 ampere (3 A) fuse must be used. less than _____ Beath High School - Int 1 Physics 51 Electrical Power Electrical energy is not free! We have to p _ a_ y for batteries to get electrical energy from them and we have to pay for the electrical energy supplied by the p o_ w _ _e _r station. The amount of energy used by a household is measured by the m e __ __ t e r at the consumer unit. Beath High School - Int 1 Physics 52 Electrical Power w _e _r rating marked on it Every appliance has a p o __ (usually in kilowatts kW, or watts W). The greater the power of the appliance, the more/less energy it uses in one second (this is because it uses more/less current). Also, the longer the time the appliance is used, the more/less energy it uses. So to save energy and money, f _ f appliances after use. always switch o _ Beath High School - Int 1 Physics 53 The Consumer Unit meter kWh Scottish Power Main Fuse Fusebox for all household circuits Mains electricity comes into a house from the power station to the consumer unit. This is where the electricity meter is Mains electricity comes from the power station into your house through a service cable which goes to the e_ t_ e_ r board. m_ Beath High School - Int 1 Physics 54 The Consumer Unit meter kWh Scottish Power Main Fuse Fusebox for all household circuits Mains electricity comes into a house from the power station to the consumer unit. This is where the electricity meter is From here the mains supply is split into various domestic c _i _ r_ c_ u_ i t_ s_ . The lights, power sockets and cooker e_ p_ a_ r_ a_ t_ e circuits which are wired in each have s _ a _r _ a_ l l_e_l_ . p_ The parallel wiring ensures each circuit has the same 230 V voltage needed to operate appliances. _____ Beath High School - Int 1 Physics 55 Mains Protection Although the fuse in the three pin plug protects the cable of the appliance, it does not protect any wiring in the house which comes from the mains supply (wires behind the w _a _l l_ s_ , etc.). Beath High School - Int 1 Physics 56 Mains Protection Household wiring is protected at the point where it comes into the house - at the consumer unit. Every circuit in the house is protected in the mains consumer unit. In older houses, a f _ u_ s_ e is used to protect each circuit but in newer houses and houses which have been recently rewired, a circuit b _ __ r e a_ k_ e _r is used. Beath High School - Int 1 Physics 57 The circuit Breaker A circuit breaker is a very fast s w _ _i t_ c_ h _ which opens and disconnects the circuit when the current gets too l a_ r_ g_ e _ . It disconnects the circuit by switching faster than a f u_ s_ e _ can by melting. This means that c _i r_ c_ u_ i_ t_ breakers are much safer and are gradually replacing fuses altogether. Beath High School - Int 1 Physics 58 Using Extensions When appliances are plugged into an extension block, the total current i n __ c_ r _ e_ a_ s_ e_ s . A kettle carries a current of about 10 amperes. If four kettles were to be plugged into an extension block, the total current being carried would be about 40 ____ amperes. This very high current causes the cables behind the wall or under the floor, to h e __ a_ t up and become a f _ i r_ e_ risk. Unfortunately, this is the cause of many house fires. Beath High School - Int 1 Physics 59 Some Safety Rules DANGER 1. Never use worn or damaged flexes: you could get a 1. s_ h_ o_ c_ k from an exposed live wire. 2. Avoid the use of extensions if possible: too many appliances connected to an extension could produce 2. o v_ e __ __ r h e_ a _t _ i n_ g_ at the socket. Beath High School - Int 1 Physics 60 Some Safety Rules DANGER 3. Always use the correct flex: a flex which is too t_ h _i n_ could overheat. 4. Always use the correct plug fuse: if the fuse rating is too high and a f _ a_ u_ l t_ develops, the flex could overheat. Beath High School - Int 1 Physics 61 Testing for Continuity Simple conductors can be tested for continuity by trying to pass a c u_ r_ r_ e_ n __ t through them in series with some indicator device (e.g. a b _ u_ l b_ or ammeter). If there is a current, the series circuit is c o __ m _p _l _ e _t _ e. If there is no current, there is a b r_ e_ a_ k _ in the circuit. Beath High School - Int 1 Physics 62 Testing for Continuity resistor to limit current A indicator (could be a lamp) item to be tested Switches can be tested, after removing them from their circuit, by using this simple continuity tester. There should be a current with the switch in the O N _ position. There should be n o_ current when the switch is changed to the OFF position. Beath High School - Int 1 Physics 63 Testing for Continuity resistor to limit current A indicator (could be a lamp) item to be tested The continuity tester must never be used with equipment connected to the mains! This simple continuity tester should not be used for components which are still c o_ n_ n_ e __ c_ t _ e_ d in their circuits. Beath High School - Int 1 Physics 64 Using a multimeter 23.04 When using the multimeter to test for faults, set the multimeter to measure r_ e _s _ i s_ t_ a_ n_ c_ e_ and place the probes across the component or circuit element. item to be tested If the reading is infinity ( a " 1 " shows on the left of e_ n circuit (this is O.K. if you the display) there is an o p __ are testing a switch set to OFF). If there is a reading, the circuit is c _ o_ m _p _l _ e _t _ e. Safety Point You must only test a component if there is no chance of there being any current in it. Beath High School - Int 1 Physics 65 Intermediate 1 Physics Practical Electricity End of Unit Beath High School - Int 1 Physics 66