Page 187 - Physics Coursebook 2015 (A level)

Chapter 12: Practical circuits
End-of-chapter questions
1 A single cell of e.m.f. 1.5 V is connected across a 0.30 Ω resistor. The current in the circuit is 2.5 A.
a b c
Calculate the terminal p.d. and explain why it is not equal to the e.m.f. of the cell. [2] Show that the internal resistance r of the cell is 0.30 Ω. [3]
It is suggested that the power dissipated in the external resistor is a maximum when its resistance R is equal to the internal resistance r of the cell.
i Calculate the power dissipated when R = r. [1]
ii Show that the power dissipated when R = 0.50 Ω and R = 0.20 Ω is less than that dissipated when R = r,
as the statement above suggests. [4] 2 A student is asked to compare the e.m.f.s of a standard cell and a test cell. He sets up the
circuit shown in Figure 12.11 using the test cell. driving cell
A
Figure 12.11 For End-of-chapter Question 2.
a i Explain why he is unable to find a balance point and state the change he must make
in order to achieve balance. [2]
ii State how he would recognise the balance point. [1]
b He achieves balance when the distance AB is 22.5 cm. He repeats the experiment with a
standard cell of e.m.f. of 1.434 V. The balance point using this cell is at 34.6 cm. Calculate the
e.m.f. of the test cell. [2]
V test cell
3 a
b When a cell is connected in series with a resistor of 2.00 Ω there is a current of 0.625 A.
4 a
State what is meant by the term e.m.f. of a cell. [2] A student connects a high-resistance voltmeter across the terminals of a battery and
observes a reading of 8.94 V. He then connects a 12 Ω resistor across the terminals and
B
Explain what is meant by the internal resistance of a cell. [2]
If a second resistor of 2.00 Ω is put in series with the first, the current falls to 0.341 A. Calculate:
i the internal resistance of the cell [2]
ii the e.m.f. of the cell. [2]
c A car battery needs to supply a current of 200 A to turn over the starter motor. Explain why
a battery made of a series of cells would not be suitable for a car battery. [2]
finds that the potential difference falls to 8.40 V.
b Explain why the measured voltage falls. [2]
c i Calculate the current in the circuit. [2]
ii Calculate the internal resistance of the cell. [2] iii State any assumptions you made in your calculations. [1]
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