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DP IB Physics: SL

Topic Questions

Home / IB / Physics: SL / DP / Topic Questions / 5. Electricity & Magnetism / 5.2 Heating Effect of Electric Currents / Structured Questions


5.2 Heating Effect of Electric Currents

Question 1a

Marks: 3

Deborah is an aspiring electrical engineer who sets out to investigate the resistivity of a metal wire. The material of the wire is unknown.

She measures the diameter of the wire using a micrometer screw gauge and takes a reading from the main scale and micrometer scale.

ymaM0DFd_q1a_heating-effect-of-electric-currents_ib-sl-physics-sq-medium

(a)
Determine the cross-sectional area of Deborah’s wire. 
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    Question 1b

    Marks: 4

    Deborah then uses an ohmmeter to measure the resistance R for different lengths L of the wire.

    Length L / cm

    Resistance R / Ω

     

    80.0

    7.94

     

    70.0

    6.99

     

    60.0

    5.89

     

    50.0

    4.93

     

    40.0

    4.27

     
    (b)
    Use Deborah’s measurements to complete the final column in the table and then determine the resistivity of the wire.
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      Question 1c

      Marks: 4
      (c)
      Suggest and explain two improvements to Deborah’s experimental method that would reduce the uncertainty in the final value of resistivity. 
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        Question 1d

        Marks: 3

        Deborah swaps the sample of wire used in her experiment for a thin film of carbon.

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        (d)
        Calculate the current which passes through the carbon film in the diagram for an applied voltage of 2.5 mV.

        The resistivity of carbon is 4.0 × 10–5 Ω m.

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          Key Concepts
          Resistivity

          Question 2a

          Marks: 4

          A current I = 10 A flows through a network of six resistors as shown.

          q2_heating-effect-of-electric-currents_ib-sl-physics-sq-medium

          The potential difference across the line XY is 8 V.

          (a)
          Calculate the value of the unknown resistance R.
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            Question 2b

            Marks: 3

            Another network, comprised of four identical resistors each of resistance 2 Ω, is connected to a 6 V battery with negligible internal resistance.

            q2b_heating-effect-of-electric-currents_ib-sl-physics-sq-medium

            (b)
            Determine the reading on the ammeter.
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              Question 2c

              Marks: 1

              A resistor is made by connecting two uniform cylinders X and Y of the same material and equal in length, in series.

              q2c_heating-effect-of-electric-currents_ib-sl-physics-sq-medium

              Cylinder Y has a resistance of 5 Ω and is twice the diameter of cylinder X.

              (c)
              Calculate the total resistance of this series combination.
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                Question 2d

                Marks: 2
                (d)
                State and explain why knowledge of quantities like resistivity is useful to scientists.
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                  Key Concepts
                  Resistivity

                  Question 3a

                  Marks: 2

                  A variable resistor R1 has a resistance that varies between 0 and 10 Ω is connected to two resistors R2 and R3 and two cells of e.m.f. 5 V and 6 V.

                  q3a_heating-effect-of-electric-currents_ib-sl-physics-sq-medium

                  (a)
                  Use Kirchhoff’s junction law to deduce an equation for three currents I1, I2 and I3 at the junction between the resistors R1, R2 and R3.   
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                    Question 3b

                    Marks: 4

                    Initially, the variable resistor R subscript 1 is set to 0 Ω.

                    (b)
                    If R2 is 5 Ω and R3 is 10 Ω, determine the current through resistor R2.
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                      Question 3c

                      Marks: 3

                      The terminals of the 5 V cell are reversed, and the variable resistor is set to a resistance of 5 Ω.

                      q3c_heating-effect-of-electric-currents_ib-sl-physics-sq-medium

                      (c)
                      Using the current directions indicated, write:
                      (i)
                      Two unique equations using Kirchhoff’s circuit law for loops.
                      (ii)
                      One equation using Kirchhoff’s circuit law for junctions.
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                        Question 3d

                        Marks: 4
                        (d)
                        Hence, calculate the power dissipated in R subscript 3.
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                          Question 4a

                          Marks: 2

                          A circuit containing four resistors is connected to a 12 V power supply.

                          q4_heating-effect-of-electric-currents_ib-sl-physics-sq-medium

                          (a)
                          Show that the potential difference between X and Y is 1 V.
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                            Question 4b

                            Marks: 3

                            A wire joins X and Y in the circuit.

                            q4b_heating-effect-of-electric-currents_ib-sl-physics-sq-medium

                            (b)
                            Assuming current flows anticlockwise from the power supply, state and explain the direction of current along the line XY.
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                              Question 4c

                              Marks: 4

                              Another potential divider circuit includes a thermistor with resistance R.

                              q4c_heating-effect-of-electric-currents_ib-sl-physics-sq-medium

                              The battery has an e.m.f. of 12 V, with negligible internal resistance. At room temperature, the resistance of the thermistor is 4.0 kΩ.

                              (c)
                              Calculate the current in the battery at room temperature, giving your answer to an appropriate number of significant figures.

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                                Question 4d

                                Marks: 4
                                (d)
                                For temperatures higher than room temperature, describe and explain how the power dissipated varies across:
                                (i)
                                AE
                                (ii))
                                BD
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                                  Question 5a

                                  Marks: 2

                                  An electronic circuit contains two resistors connected as shown.

                                  q5_heating-effect-of-electric-currents_ib-sl-physics-sq-mediumq5-2_heating-effect-of-electric-currents_ib-sl-physics-sq-medium

                                  The material from which each resistor is made has a resistivity of 2.0 × 105 Ω m and both resistors have dimensions of 15 mm by 2.3 mm by 1.3 mm.

                                  (a)
                                  Calculate the total resistance of the electronic circuit.
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                                    Question 5b

                                    Marks: 2

                                    The circuit is designed such that changes to the dimensions of each resistor by a common factor x are easily accomplished.

                                    (b)
                                    Show that if the dimensions of each resistor are increased by a factor of x then the resistance decreases by the same factor.
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                                      Question 5c

                                      Marks: 4

                                      An electrical heating element is made of nichrome wire of resistivity 1.1 × 10–6 Ω m. It is required to dissipate 800 W when connected to the 230 V mains supply. The radius of the wire is 0.17 mm.

                                      (c)
                                      Calculate the length of wire required for the heating element.
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                                        Question 5d

                                        Marks: 2
                                        (d)
                                        Suggest two properties that the nichrome wire must have to make it suitable as an electrical heating element.
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