Electricity Part II -Questions
1. Explain the two methods of connecting resistors in circuits with the help of circuit diagrams. 2. Write the formulae to calculate the effective resistances when resistors are connected (a) in series and (b) in parallel. 3. How is the total potential difference calculated across a combination of resistors in series? 4. Example 12.7 An electric lamp, whose resistance is 20 Ω, and a conductor of 4 Ω resistance are connected to a 6 V battery (Fig. 12.9). Calculate (a) the total resistance of the circuit, (b) the current through the circuit, and (c) the potential difference across the electric lamp and conductor. 5. Example 12.8
In the circuit diagram given in Fig. 12.10, suppose the resistors R1, R2 and R3 have the values 5Ω , 10 Ω , 30Ω , respectively, which have been connected to a battery of 12 V. Calculate (a) the current through each resistor, (b) the total current in the circuit, and (c) the total circuit resistance.
6. Example 12.9
If in Fig. 12.12, R1 = 10Ω , R2 = 40Ω , R3 = 30Ω , R4 = 20 Ω, R5 = 60Ω , and a 12 V battery is connected to the arrangement. Calculate (a) the total resistance in the circuit, and (b) the total current flowing in the circuit. 7. Why are electrical gadgets connected in parallel not in series? T. Q U E S T I O N S
8. 1. Draw a schematic diagram of a circuit consisting of a battery of three cells of 2 V each, a 5 Ω resistor, an 8 Ω resistor, and a 12 Ω resistor, and a plug key, all connected in series. 9. 2. Redraw the circuit of Question 1, putting in an ammeter to measure the current through the resistors and a voltmeter to measure the potential difference across the 12 Ω resistor. What would be the readings in the ammeter and the voltmeter? 10. 1. Judge the equivalent resistance when the following are connected in parallel – (a) 1 Ω and 106Ω , (b) 1Ω and 103Ω , and 106Ω . 11. 2. An electric lamp of 100Ω, a toaster of resistance 50Ω, and a water filter of resistance 500Ω are connected in parallel to a 220 V source. What is the resistance of an electric iron connected to the same source that takes as much current as all three appliances, and what is the current through it? 12. 3. What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series? 13. 4. How can three resistors of resistances 2Ω, 3Ω, and 6Ω be connected to give a total resistance of (a) 4Ω, (b) 1Ω? 14. 5. What is (a) the highest, (b) the lowest total resistance that can be secured by combinations of four coils of resistance 4 Ω, 8 Ω, 12Ω , 24Ω ? 15. Distinguish between resistors in series and in parallel.
Electricity part II (Questions & answers)
1. Explain the two methods of connecting resistors in circuits with the help of circuit diagrams. Resistors can be in series and in parallel.
A series circuit is a circuit in which resistors are arranged in a chain, so the current has only one path to take. The current is the same through each resistor. The total resistance of the circuit is found by simply adding up the resistance values of the individual resistors. Equivalent resistance of resistors in series : R = R1 + R2 + R3 + ...
A parallel circuit is a circuit in which the resistors are arranged with their heads connected together, and their tails connected together. The current in a parallel circuit breaks up, with some flowing along each parallel branch and re-combining when the branches meet again. The voltage across each resistor in parallel is the same. [pic]
The total resistance of a set of resistors in parallel is found by adding up the reciprocals of the resistance values, and then taking the reciprocal of the total: Equivalent reciprocal of resistance of resistors in parallel: 1 / R = 1 / R1 + 1 / R2 + 1...
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