Transcript capacitor
capacitor They are important in both electric & electronic circuit • Have you seen any of them before ? Function : • Capacitors can store and then release electrical energy . • The value of a capacitors is often measured in micro-farads . • The amount of energy stored by the capacitor depends on : How much charged is moved on to the plates . • The conducting plates are separated by an insulating material which is called the Dielectric Charging a capacitor : What happens when the switch closed ? Discharging capacitor : if the battery is removed , we can discharge the capacitor + _ Why does the direction of charging current in the opposite way of current of the battery ? The charging & discharging processes happen very quickly .Can we slow them down ? Capacitance • The ability of a capacitor to store charge on its plates. • The large the capacitance , the more charge the capacitor stores for each volt applied across its plates . In fact : • Capacitance = charge / voltage • C=Q/V How can we measured the charge on the capacitor plates ? Measuring capacitance : Complete the table : t(s) I(µ A) 0 60 0 10 60 1.2 20 60 2.4 30 60 3.6 40 60 4.8 Q=It C) µ( V ( v) C=Q/V (µ F) The energy of a charged capacitor • A B Questions : • Q1:What happens to the switch in position A? • Q2:What happens to the switch in position B? • Q3:Where did this energy come from ? • The p.d. across the capacitor and the size of its capacitance , both affect the energy stored . • Energy stored =0.5Xcapacitance X (voltage)2 W = 0.5 X C X V2 OR W = 0.5 X Q X V Q1 • A capacitor is charged using a current of 20µA from a 5volts supply .After 55s it is fully charged. • Calculate : • A. Q? • B. C? • C. W? More Qs. • http://electronics.howstuffworks.com/solidstate-electronics-channel.htm http://us.c2w.com/quizzes/45045capacitor-quiz Capacitor in parallel Here are 3 facts that you should know for • The p.d. across each capacitors is the same & equal to V . • The total Q is the sum Q = Q1+Q2 • The total C is the sum C = C1+C2 Q=CV Capacitor in series Here are 3 facts that you should know for • The Q. across each capacitors is the same & equal to Q . • The total V is the sum V= V1+V2 • The total C is the sum 1/C = 1/C1+ 1/C2 V Capacitors in Parallel Same Capacitors in sires V = v1+v2 Q Q = Q1+Q2 Same C C =C1+C2 1/C = 1/C1 + 1/C2 Qs. • Q1: Calculate the charge on each capacitor in this diagram : • If : • V=5volt • C1=500 micro farad C2=300 micro farad Qs.: Pg. 273 , Q:6 Home Work : Pg. 273 , Q :1-3-4-5