page 1 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 4 Department of Information and Communications Technology Power, Series Circuits, Circuit Ground Power, Series Circuits, Circuit Ground e OBJECTIVES  Definition of Power  Compute power in simple circuits  Determine the total resistance in a series circuit  Express Kirchoff’s voltage law and use it to analysis a given circuit  Use of the the voltage divider rule  Solve for power dissipated in any resistor in a series circuit  Describe the loading effect of an ammeter in a circuit  Potential Difference and Circuit Ground

page 2 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 4 Department of Information and Communications Technology Power, Series Circuits, Circuit Ground Notation of D.C. quantities e Direction of V and I e Source Load

page 3 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 4 Department of Information and Communications Technology Power, Series Circuits, Circuit Ground Definition of Power

page 4 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 4 Department of Information and Communications Technology Power, Series Circuits, Circuit Ground P is a measure of the rate of energy conversion

page 5 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 4 Department of Information and Communications Technology Power, Series Circuits, Circuit Ground Example e Compute the power supplied to the electric heater shown below, using all three power formula.

page 6 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 4 Department of Information and Communications Technology Power, Series Circuits, Circuit Ground SERIES CIRCUITS (1)

page 7 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 4 Department of Information and Communications Technology Power, Series Circuits, Circuit Ground SERIES CIRCUITS (2)

page 8 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 4 Department of Information and Communications Technology Power, Series Circuits, Circuit Ground SERIES CIRCUITS (3)

page 9 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 4 Department of Information and Communications Technology Power, Series Circuits, Circuit Ground SERIES CIRCUITS (4) e Series connection of two resistors: e Prove the series resistance expression using the equivalent concept.

page 10 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 4 Department of Information and Communications Technology Power, Series Circuits, Circuit Ground Voltage Divider Rule e For the two resistors case, the voltage divider rule is: e In general, for any number of resistors, the voltage drop across any resistor may be found as:

page 11 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 4 Department of Information and Communications Technology Power, Series Circuits, Circuit Ground Solve for power dissipated in any resistor in a series circuit

page 12 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 4 Department of Information and Communications Technology Power, Series Circuits, Circuit Ground Ammeter Loading effect e Loading effect refers to those undesirable effects as a result of load insertion to a circuit. e When we use an ammeter to measure to measure the current of a circuit, the ammeter is inserted into the circuit in SERIES. e The ammeter will have a small resistance, Ra, this will alter the current to:

page 13 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 4 Department of Information and Communications Technology Power, Series Circuits, Circuit Ground Potential difference e Potential difference (p.d.) (unit in volts) \ P.d.is a voltage gradient between any two points in a circuit. (Current flows from high to low potential level) \ P.d. across a passive component is called a voltage drop iP.d.s across R 1 and R 2 are the same (i.e. V 1 =V 2 ) iVoltage at A (V s ) is twice voltage at B (V 2 ) \ P.d. is a vector quantity (mag. & direction) \ P.d. is a relative magnitude \ P.d. is always across two points \ 0 volt is typically chosen as the reference voltage for a system or circuit.This is referred to as the GROUND.

page 14 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 4 Department of Information and Communications Technology Power, Series Circuits, Circuit Ground Voltage measurement

page 15 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 4 Department of Information and Communications Technology Power, Series Circuits, Circuit Ground Example of incorrect grounding technique One of the input of the voltmeter is grounded, an attempt to measure the non-grounded voltage between points A and B of the circuit results in short-circuiting point B to ground. The voltage value measured will be erroneous.