Name: Date: Electric Currents 2. A battery is connected in series with a resistor R. The battery transfers 2 000 C of charge completely round the circuit. During this process, 2 500 J of energy is dissipated in the resistor R and 500 J is expended in the battery. The emf of the battery is A. 2.00. B..25. C. 0.75. D. 0.50. 2. The element of an electric heater has a resistance R when in operation. What is the resistance of a second heater that has a power output three times as large at the same operating voltage? A. B. R 9 R 3 C. 3R D. 9R 3. A resistor of resistance.0 Ω is connected in series with a battery. The current in the circuit is 2.0 A. The resistor is now replaced by a resistor of resistance of 4.0 Ω. The current in this circuit is.0 A. 2.0 A.0 A.0 Ω 4.0 Ω The best estimate for the internal resistance of the battery is A..0 Ω. B. 2.0 Ω. C. 4.0 Ω. D. 5.0 Ω.
4. n the circuit shown, the voltmeter has a resistance of 20 kω and the battery has an emf of 6.0 and negligible internal resistance. 6.0 0 kω 20 kω 20 kω The reading on the voltmeter is A. 2.0. B. 3.0. C. 4.0. D. 6.0. 5. The graph shows the variation with applied potential difference of the current in an electrical component. P 0 0 v Which one of the following gives the resistance of the component at point P? A. The gradient of the line at P B. The reciprocal of the gradient of the line at P C. The ratio D. The ratio 2
6. n the circuit shown below, the cell has negligible internal resistance. 2R 3 R 2 Which of the following equations is correct? A. = 2 2 B. = 2 3 C. 2 = 2 3 D. 3 = 2 7. Two filament lamps X and Y are designed to operate at normal brightness when the potential difference across the lamps is 6. Each lamp will just light when the potential difference across it is 3. The two lamps are connected in parallel to a 4 supply of negligible internal resistance as shown below. 4 X The filament of lamp X breaks so that there is no current in it. The filament of lamp Y will A. glow at normal brightness. B. glow at more than normal brightness. C. glow more dimly. Y D. stay at the same brightness. 3
8. Three resistors P, Q and R, are each labelled 00 Ω. They are connected as shown. Q X P R Y The total resistance, when measured between points X and Y, is found to be 200 Ω. What is the correct explanation for the resistance reading? A. Resistor R is zero B. Resistor R is infinite C. Resistor P is zero D. Resistor P is infinite 9. A heater has a resistance R when the potential difference across it is 2. n the circuit below, it is connected in series with a 36 supply and a resistor S. 36 S To ensure that the potential difference across the heater is 2, the resistance of the resistor S should be A. R. 2 B. 2R. 3 C. 3R. 2 D. 2R. 4
0. n the circuit below, which meter is not correctly connected? A 3 A 2 4 A. B. 2 C. 3 D. 4. This question is about a filament lamp. (a) On the axes below, draw a sketch-graph to show the variation with potential difference of the current in a typical filament lamp (the characteristic). (Note: this is a sketch-graph; you do not need to add any values to the axes). 0 0 (b) (i) Explain how the resistance of the filament is determined from the graph. (ii) Explain whether the graph you have sketched indicates ohmic behaviour or non-ohmic behaviour. 5
A filament lamp operates at maximum brightness when connected to a 6.0 supply. At maximum brightness, the current in the filament is 20 ma. (c) (i) Calculate the resistance of the filament when it is operating at maximum brightness. (ii) You have available a 24 supply and a collection of resistors of a suitable power rating and with different values of resistance. Calculate the resistance of the resistor that is required to be connected in series with the supply such that the voltage across the filament lamp will be 6.0. (2) (Total 6 marks) 2. This question is about emf and internal resistance. A dry cell has an emf E and internal resistance r and is connected to an external circuit. There is a current in the circuit when the potential difference across the terminals of the cell is. r E (a) State expressions, in terms of E,, r and where appropriate, for (i) the total power supplied by the cell; (ii) the power dissipated in the cell; 6
(iii) the power dissipated in the external circuit. (b) Use your answers to (a) to derive a relationship between, E, and r.......... (2) The graph below shows the variation of with for the dry cell..6.5.4.3.2..0 0.90 / 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.0 0.0 0.0 0.0 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90.0..2.3 / A 7
(c) Complete the diagram below to show the circuit that could be used to obtain the data from which the graph was plotted. (3) (d) Use the graph, explaining your answers, to (i) determine the emf E of the cell; (2) (ii) determine the current in the external circuit when the resistance R of the external circuit is very small; (2) (iii) deduce that the internal resistance r of the cell is about.2 Ω. (3) 8
(e) The maximum power dissipated in the external circuit occurs when the resistance of the external circuit has the same value as the internal resistance of the cell. Calculate the maximum power dissipation in the external circuit............. (3) (Total 8 marks) 3. Specific heat and a domestic shower (a) Define specific heat capacity.......... (b) Equal masses of two different solid substances A and B are at the same temperature. The specific heat capacity of substance A is greater than the specific heat capacity of substance B. The two substances now have their temperatures raised by the same amount. Explain which substance will have the greater increase in internal energy assuming both remain in the solid phase............. (2) (c) The diagram below shows part of the heating circuit of a domestic shower. Cold water enters the shower unit and flows over an insulated heating element. The heating element is rated at 7.2 kw, 240. The water enters at a temperature of 4 C and leaves at a temperature of 40 C. The specific heat capacity of water is 4.2 03 J kg K. 9
(i) Estimate the flow rate of the water. (4) (ii) Suggest one reason why your answer to (c)(i) is only an estimate. (Total 8 marks) 0