Page 164 - Physics Coursebook 2015 (A level)

Cambridge International AS Level Physics
QUESTION
23 a
A 10 V power supply of negligible internal resistance is connected to a 100 Ω resistor. Calculate the current in the resistor.
b An ammeter is now connected in the circuit, to measure the current. The resistance of the ammeter is 5.0 Ω. Calculate the ammeter reading.
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Summary
■■ Kirchhoff’s first law states that the sum of the current currents entering any point in a circuit is equal to the sum of the currents leaving that point.
■■ Kirchhoff’s second law states that the sum of the e.m.f.s around any loop in a circuit is equal to the sum of the p.d.s around the loop.
■■ The combined resistance of resistors in series is given by the formula:
R = R1 + R2 + ...
■■ The combined resistance of resistors in parallel is given by the formula:
1 = 1 + 1 + ... R R1 R2
■■ Ammeters have a low resistance and are connected in series in a circuit.
■■ Voltmeters have a high resistance and are connected in parallel in a circuit.
End-of-chapter questions
1 Use Kirchhoff’s first law to calculate the unknown currents in the examples in Figure 10.24. In each example state the direction of the current.
[4]
a b
W
3.6 A 4.3 A Figure 10.24 For End-of-chapter Question 1.
2.4 A c X
Y
2.7 A d 4.8 A
4.3 mA
4.3 mA
Z