Revision Questions on Current and Potential Difference (1)

Wherever you see an input box in the following text, please fill in the correct words or numbers (to 2 d.p. where appropriate). You might well need a calculator to do this, so here are some links to a few online calculators. They all open up in new tabs, and at least one of them should work!

https://www.calculator.net/scientific-calculator.html
https://www.geogebra.org/scientific
https://web2.0calc.com/

  1. A student wants to investigate how the current through a filament lamp affects its resistance. She has access to the following components: 12 volt battery, filament lamp, variable resistor, voltmeter, ammeter.

    1. Please type the name of one of these components in each box below to make the circuit on the right suitable for the student to use in his experiment [2 marks]:

    2. Describe how the student could use his circuit to investigate how the current through a filament lamp affects its resistance. [4 marks]


    3. The student's results are shown in the graph. Describe how the resistance of the filament lamp changes as the current through it increases. [1 mark]


    4. Use the graph to estimate the resistance of the filament lamp when a current of 0.10A passes through the lamp. [1 mark]
      Resistance = Ω.

    5. The current-potential difference graphs of three components are shown below. Use answers from this list to identify each component: diode, filament lamp, light dependent resistor, resistor at constant temperature, thermistor

  2. A student investigated how current varies with potential difference for two different lamps. His results are shown in the graph.

    1. The student used a 12V battery in his experiment. Draw a diagram of a circuit that he could have used to take his measurements. [3 marks]

    2. Which lamp will be brighter at any given potential difference? Explain your answer. [2 marks]
      Answer: Lamp

    3. Which lamp has the higher resistance? Explain your answer. [2 marks]
      Answer: Lamp

    4. Both lamps behave like ohmic conductors through a range of values of potential difference. Use the graph to determine the range for these lamps. Explain your answer. [3 marks]

  3. The diagram on the right shows the apparatus used to investigate how the current through a thermistor depends on the temperature of the thermistor.

    1. Which one of the following is the correct circuit symbol for a thermistor? [1 mark]
      A.        B.        C.

    2. To get a range of results, hot water at 60oC was poured into the beaker. The temperature of the water and current through the thermistor were then recorded as the water cooled. The results of the investigation are shown in this graph. Suggest one way the investigation could have been changed to give a wider range of temperatures. [1 mark]


    3. Describe how the current through the thermistor depends on the temperature of the thermistor. [1 mark]


    4. Determine the current through the thermistor at 40oC. [1 mark] Amps.

    5. At 40oC, the thermistor has a resistance of 250Ω. Calculate the potential difference across the thermistor [2 marks]:

    6. The potential difference across the thermistor stays the same all through the investigation. Complete the following sentence with words/phrases from this list [1 mark]: increases, stays the same, decreases

      As the temperature of the thermistor decreases, its resistance

  4. The diagram on the right shows the inside of a battery pack designed to hold three identical 1.5 V cells.

    1. Which one of the following arrangements would give a 4.5V output across the battery pack terminals T? [1 mark] Answer:

      A. B. C. D.

    2. The circuit on the right shows a variable resistor and a fixed value resistor connected in series in a circuit. Explain how an ammeter might be connected to measure the current in the circuit. [1 mark]


    3. The graph on the right shows how the reading on voltmeter V1 and the reading on voltmeter V2 change as the resistance of the variable resistor changes. Calculate the potential difference of the battery: Volts.

    4. Calculate the resistance of the fixed resistor R [2 marks]: Ω

    5. Calculate the current through the circuit when the resistance of the variable resistor equals 200Ω: A

  5. The diagram on the right shows a three-pin plug.

    1. Name the materials used in the structure of a plug. Give the reason why each material is used. [1 mark]


    2. The three-pin plug contains a fuse. The fuse is connected to one of the wires inside the cable. Which one of the wires inside the cable is the fuse connected to? The fuse is connected to the wire. [1 mark]

    3. The fuse is a thin wire inside a closed glass tube. The wire acts as a resistor. What effect does a current through a wire have on the wire? [1 mark]


    4. A washing machine is connected to the mains electricity via a three-pin plug containing a fuse. The power of the washing machine varies between 0.7kW and 2kW depending on which part of the wash cycle is operating. Calculate the maximum current drawn from the mains electricity supply by the washing machine. The mains electricity supply is at a potential difference of 230V. [2 marks]
      Current = A

    5. The digram on the right shows how the mains electricity cable is connected to the washing machine. The earth wire is connected to the metal case of the washing machine. If a fault makes the metal case live, the earth wire and fuse inside the plug prevent the mains cable from overheating and causing a fire. Explain how. [2 marks]


    6. New research has shown that many people underestimate the hazards of using mains electricity. It is important that people do understand the hazards of using mains electricity. Suggest why. [1 mark]

  6. The current in a circuit depends on the potential difference provided by the cells and the total resistance of the circuit.

    1. The diagram shows the graph of current against potential difference for a component. What is the name of the component? [1 mark]

    2. In the circuit shown below, two resistors, X and Y, are connected in parallel to a 6V battery.
      What is the potential difference across X? [1 mark] V.

    3. Calculate the resistance of X. [2 marks] Ω

    4. What is the current in Y? [1 mark] Amp

    5. Calculate the resistance of Y. [1 mark] Ω

    6. Complete the following sentences with one of the following: decreases, stays the same, increases [3 marks]:

      When the temperature of resistor X increases, its resistance increases. The potential difference across X , the current in X and the total current in the circuit

  7. The graph on the right shows the current−potential difference graph for three wires, A, B and C.

    1. From the graph, how can you tell that the temperature of each wire was held constant? [1 mark]


    2. Which one of the wires, A, B or C, has the greatest resistance? [1 mark]
      Give a reason for your answer:


    3. A student measured the resistance of four other wires, J, K, L and M:
      Wire Type of metal Length in cm Diameter in mm Resistance in ...
      J copper 50 0.17 0.36
      K copper 50 0.3 0.12
      L copper 100 0.3 0.24
      M constantan 100 0.3 7.00
      The last column of the table should include the unit of resistance. What is the unit of resistance? [1 mark]

    4. The resistance of a wire depends on several factors. Look at the table. Which two wires from J, K, L and M show that the resistance of a wire depends on the length of the wire? [1 mark] Wire

    5. A student looked at the data in the table and wrote this conclusion: "The resistance of a wire depends on the type of metal from which the wire is made." The student could not be certain that her conclusion is true for all types of metal. Suggest what extra data is needed for the student to be more certain that the conclusion is correct. [1 mark]


    6. The student used the circuit on the right to measure the resistance of each wire, with a voltmeter connected into it. Four possible positions of the voltmeter are shown. Which position is correct for the student to measure the resistance of the wire?

  8. A student uses the circuit shown to measure the resistance of resistor R.

    1. Describe how a student would use the circuit to take the readings necessary to determine the resistance of resistor R. [6 marks]


    2. Explain why the student should open the switch after each reading. [2 marks]


    3. In an experiment using this circuit, an ammeter reading was 0.75A. The calculated value of the resistance of resistor R was 16Ω. What is the voltmeter reading? [2 marks] Volts

    4. In answering the previous part, what assumption are you making about the voltmeter?[2 marks]


    5. The student told his teacher that the resistance of resistor R was 16Ω. The teacher explained that the resistors used could only have one of the following values of resistance: 10Ω, 12Ω, 15Ω, 18Ω, 22Ω. Suggest which of these resistors the student had used in his experiment. Give a reason for your answer. [2 marks] Ω

    6. Describe the purpose of a fuse in a circuit. Why are fuses generally not used in circuits powered by batteries? [2 marks]