Transcript Electricity
UNIT 1: ELECTRICITY AND ELECTRONICS (PART 2) TECHNOLOGIES ESO 3 ELECTRICITY AND ELECTRONICS 4. TYPES OF CIRCUITS 4.1 SERIES CIRCUITS 4.2 PARALLEL CIRCUITS 4.3 MEASURING CURRENT AND VOLTAGE 4.4 MIXED CIRCUITS 5. TYPES OF CURRENT: 5.1 DIRECT CURRENT (DC) 5.2 ALTERNATING CURRENT (AC) 4. TYPES OF CIRCUITS Components of an electrical circuit or electronic circuit can be connected in many different ways. The two simplest of these are called series and parallel and occur very frequently. 4.1 SERIES CIRCUITS Components connected in series are connected along a single path, so the same current flows through all of the components. If you follow the circuit diagram from one side of the cell to the other, you should pass through all the different components, one after the other, without any branches. 4. TYPES OF CIRCUITS 4.1 SERIES CIRCUITS (continue) In a series circuit, if a lamp breaks or a component is disconnected, the circuit is broken and all the components stop working. If you put more lamps into a series circuit, the lamps will be dimmer than before. The voltage is divided among the different elements in the circuit. 4. TYPES OF CIRCUITS 4.1 SERIES CIRCUITS (continue) - TOTAL RESISTANT or EQUIVALENT RESISTANT is: Rt = R1 + R2 (+ R3, etc) - If several generators are connected in series, the voltage will be: 4. TYPES OF CIRCUITS 4.2 PARALLEL CIRCUITS In parallel circuits different components are connected on different branches of the wire. If you follow the circuit diagram from one side of the cell to the other, you can only pass through all the different components if you follow all the branches. The current is shared between each component connected in parallel. The total amount of current flowing into the junction, or split, is equal to the total current flowing out. The current is described as being conserved. 4. TYPES OF CIRCUITS 4.2 PARALLEL CIRCUITS (Continue) In a parallel circuit, if a lamp breaks or a component is disconnected from one parallel wire, the components on different branches keep working. And, unlike a series circuit, the lamps stay bright if you add more lamps in parallel. This happens because all elements in the circuit have the same voltage. 4. TYPES OF CIRCUITS 4.2 PARALLEL CIRCUITS (Continue) - TOTAL RESISTANT or EQUIVALENT RESISTANT is: 4. TYPES OF CIRCUITS VIDEO: http://www.bbc.co.uk/education/guides/zddp34j/activity QUESTION: Which of the circuits here are connected in series, and which are connected in parallel? 4. TYPES OF CIRCUITS 4.3 MEASURING VOLTAGE AND CURRENT HOW TO MEASURE CURRENT: Ammeters are used to measure current. To measure the current flowing through a component in a circuit, you must connect the ammeter in series with it. HOW TO MEASURE VOLTAGE: Voltage is a measure of the difference in electrical energy between two parts of a circuit. The bigger the difference in energy, the bigger the voltage. Voltage is measured using a voltmeter. To measure the voltage across a component in a circuit, you must connect the voltmeter in parallel with it. 4. TYPES OF CIRCUITS 4.4 MIXED CIRCUITS Some elements are connected in series and some in parallel: RT = RP + RS; 1/Rp= 1/10 + 1/7; RP = 4,1k; RT = 5k + 4,1k = 9,1k IT = VT/RT; IT = 9V/9,1k= 0,98 mA V5k=IT·R5k = 0,98 mA·5k= 4,9 V ; V7k=V10k = 9V-4,9V = 4,1 V I7k = V7k/R7k = 4,1V / 7k = 0,58 mA ; I10k= 4,1V/10k = 0,41 mA (IT = I7k + I10k = 0,58mA+0,41mA=0,99mA) Rs = 250+1000=1250Ω; 1/RT= 1/Rp= 1/100 + 1/1250; RT = 92,6Ω IT = VT/RT; IT = 9V/92,6Ω = 0,097A; V100= 9V; I100=V100/R100 = =9V/100Ω=0,09A; IT=I100+I1250; I1250=0,097A-0,09A=0,007A; V250=0,007A·250=1,75V; V1k = 9-1,75V = 7,25V Rs = 10k+10k=20k; 1/RT= 1/Rp= 1/20 + 1/10; RT = 6,7k IT = VT/RT; IT = 9V/6,7k = 1,34mA; V10k= 9V; I10k=V10k/R10k = =9V/10k=0,9mA; IT=I10k+I20k; I20k=1,34-0,9=0,44mA; V10k-10k=0,44mA·10k=4,4V 5. TYPES OF CURRENT 5.1 DIRECT CURRENT If the current flows in only one direction it is called direct current, or DC. Batteries and solar cells supply DC electricity. A typical battery may supply 1.5 V. The diagram shows an oscilloscope screen displaying the signal from a DC supply. 5.2 ALTERNATING CURRENT If the current constantly changes direction it is called alternating current, or AC. Mains electricity is an AC supply. The Spain mains supply is about 230 V. It has a frequency of 50 Hz, which means that it changes direction and back again 50 times a second. The diagram shows an oscilloscope screen displaying the signal from an AC supply.