1. page 1 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 5 Department of Information and Communications Technology Parallel Circuits Parallel Circuits e OBJECTIVES  Calculate the total resistance and conductance of a network of parallel resistors iDetermine the current in any resistor in a parallel circuit  Solve for the voltage across any parallel combination of resistors,  Apply Kirchoff’s current law to solve for unknown currents in a circuit,  Explain why voltage source of different magnitude must never be connected in parallel  Current divider rule  Describe voltmeter loading effect  Understand OPEN and SHORT circuit

2. page 2 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 5 Department of Information and Communications Technology Parallel Circuits Parallel Circuits Definitions e Parallel Circuits Elements or branches are said to be in a parallel connection when they have exactly two nodes in common.

3. page 3 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 5 Department of Information and Communications Technology Parallel Circuits Kirchoff's Current Law e Kirchoff's Current Law e The summation of current entering a node is equal to the summation of currents leaving the node.

4. page 4 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 5 Department of Information and Communications Technology Parallel Circuits Parallel connection of two resistors

5. page 5 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 5 Department of Information and Communications Technology Parallel Circuits Resistors in Parallel

6. page 6 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 5 Department of Information and Communications Technology Parallel Circuits Voltage Sources in Parallel e Voltage sources in parallel e Voltage sources of different potentials must never be placed in parallel.

7. page 7 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 5 Department of Information and Communications Technology Parallel Circuits Current divider rule

8. page 8 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 5 Department of Information and Communications Technology Parallel Circuits Analysis of series-parallel circuits For the circuit shown above, a. Find R T. b. Calculate I 1,I 2,and I 3. C. Determine the Voltage V 1 and V 2.

9. page 9 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 5 Department of Information and Communications Technology Parallel Circuits Voltmeter Loading effect e Voltmeter Loading effect refers to those effects as a result of placing an voltmeter across the two insertions into a circuit. e What kinds of loading effect are likely in the measurements below ? V s R l R L Voltmeter

10. page 10 Hong Kong Institute of Vocational Education (Tsing Yi) T&N 3311 Lec 5 Department of Information and Communications Technology Parallel Circuits Opened vs Shorted Circuit Source No current flows in an “opened” circuit. Open circuit voltage refers to the output voltage of a source at “no load” Source No voltage develops across a “shorted” circuit