# ELECTRIC CIRCUITS 30 SEPTEMBER 2014

```REVISION: ELECTRIC CIRCUITS
30 SEPTEMBER 2014
Lesson Description
In this lesson, we revise:
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

Ohm’s Law
Electric Circuit Problems
Electric Energy &amp; Power
Ohm’s Law
Question 1
120 J of work is done when 15 C of charge moves through a light bulb in 300 seconds. Calculate the:
1.1
potential difference across the light bulb
1.2
current in the light bulb.
1.3
resistance of the light bulb
Question 2
A battery of four 1,5 V cells, an ammeter and three resistors of 2Ω, 4Ω and 6Ω are connected in
series to form a circuit.
2.1
Draw a circuit diagram of the circuit
2.2
Calculate the reading on the ammeter
2.3
What would the reading of a voltmeter be when connected across the 4Ω resistor?
Electric Circuit Problems
Question 1
In the circuit represented below, a battery of emf 30 V and
unknown internal resistance r are connected to resistors, as
shown. Ignore the resistance of the ammeter and the
connecting wires.
The current passing through the 10 Ω resistor is 0,6 A.
Calculate the:
1.1
Equivalent resistance of the two resistors in parallel
1.2
Current through the 8 Ω resistor.
1.3
Internal resistance of the battery.
Question 2
In the circuit represented below, two 60 Ω resistors connected in parallel are connected in series with
a 25 Ω resistor. The battery has an emf of 12 V and an internal resistance of 1,5 Ω.
Calculate the …
2.1
Equivalent resistance of the parallel combination.
2.2
Total current in the circuit.
2.3
Potential difference across the parallel resistors.
Electric Energy &amp; Power
Question 1
The element of a heater has a resistance of 54 Ω. A current of 5A flows through it for 30 minutes.
Calculate the ….
1.1 Power dissipated by the element of the heater.
1.2 Amount of heat energy given off by the element during the 30 minute period.
Question 2
A lawnmower is marked 2000 W. A man operates it for 2 hours cutting grass inside his yard.
Calculate
2.1 The energy consumed by the loan mower whilst the man operates it.
2.2 How much it will cost the mass to operate the loan mower for 2 hours if cost of electricity is 59
cents per unit.
Question 3
A battery of four 1,5V cells connected in series has no internal resistance and is connected to an
ammeter and three identical light bulbs as shown in the circuit diagram below
When the switch S1 is open the ammeter reads 1A
3.1
What would you observe about the brightness of the two bulbs?
The switch is now closed
3.2
Explain what you would observe about the brightness of the bulbs by doing a calculation
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