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ASPhysicsCIEExam Questions9. Electricity9.1 Current & Potential Difference

Current & Potential Difference (CIE AS Physics)

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9.1 Current & Potential Difference

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9.1 Current & Potential Difference

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11 mark

What describes the electric potential difference between two points in a wire that carries a current?

  • the force required to move a unit positive charge between the points

  • the ratio of the energy dissipated between the points to the current

  • the ratio of the power dissipated between the points to the current

  • the ratio of the power dissipated between the points to the charge moved

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21 mark

When there is no current in a wire, which statement about the conduction electrons in that wire is correct?

  • electrons in the wire are moving totally randomly within the wire

  • equal numbers of electrons move at the same speed, but in opposite directions, along the wire

  • no current is flowing therefore the electrons in the wire are stationary

  • no current is flowing therefore the electrons in the wire are vibrating around a fixed point

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31 mark

A filament lamp has a resistance of 180 Ω when the current in it is 500 mA.

 What is the power transformed in the lamp?

  • 45 W

  • 50 W

  • 90 W

  • 1400 W

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41 mark

When will 1 C of charge pass a point in an electrical circuit?

  • when 1 A moves through a potential difference of 1 V

  • when a power of 1 W is used for 1 s

  • when the current is 5 mA for 200 s

  • when the current is 10 A for 10 s

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51 mark

There is a current of 10 mA in a conductor for half an hour.

 How much charge passes a point in the conductor in this time?

  • 0.3 C

  • 5 C

  • 18 C

  • 300 C

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61 mark

The diagram shows the symbol for a wire carrying a current I

cie-ial-images423png

What does this current represent?

  • the amount of charge flowing past a point in XY per second

  • the number of electrons flowing past a point in XY per second

  • the number of positive ions flowing past a point in XY per second

  • the number of protons flowing past a point in XY per second

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71 mark

A 12 V battery is charged for 20 minutes by connecting it to a source of electromotive force (e.m.f.). The battery is supplied with 7.2 × 104 J of energy in this time.

 How much charge flows into the battery?

  • 5.0 C

  • 60 C

  • 100 C

  • 6000 C

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81 mark

The diagram shows four heaters and the current in each.

 Which heater has the greatest power dissipation ?

cie-ial-physics-images-9-1-e-q8-

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    91 mark

    Which equation that links some of the following terms is correct?

     

    potential difference (p.d.)

    V

    current

    I

    resistance

    R

    charge

    Q

    energy

    E

    power

    P

    time

    t

    • P equals fraction numerator Q squared R over denominator t end fraction

    • E R squared equals V squared t

    • fraction numerator V I over denominator P end fraction equals t

    • P Q equals E I

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    101 mark

    A copper wire of cross-sectional area 2.0 mm2 carries a current of 10 A.

     How many electrons pass through a given cross-section of the wire in one second?

    • 1.0 × 101

    • 5.0 × 106

    • 6.3 × 1019

    • 3.1 × 1025

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    11 mark

    The diagrams show two different circuits.

    cie-ial-images428png

    The cells in each circuit have the same electromotive force and zero internal resistance. The three resistors each have the same resistance R.

     In the circuit on the left, the power dissipated in the resistor is P.

     What is the total power dissipated in the circuit on the right?

    • P over 4

    • P over 2

    • P

    • 2P

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    21 mark

    The potential difference across a component in a circuit is 2.0 V.

    How many electrons must flow through this component in order for it to be supplied with 4.8 J of energy?

    • 2.6 × 1018

    • 1.5 × 1019

    • 3.0 × 1019

    • 6.0 × 1019

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    31 mark

    Two lamps are connected in series to a 250V power supply. One lamp is rated 240V, 60W and the other is rated 10V, 2.5W.

     Which statement most accurately describes what happens ?

    • both lamps light at less than their normal brightness

    • both lamps light normally

    • only the 60 W lamp lights

    • the 10 V lamp blows

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    41 mark

    Two copper wires of the same length but different diameters carry the same current.

     Which statement about the flow of charged particles through the wires is correct?

    • charged particles are provided by the power supply, therefore, the speed at which they travel depends only on the voltage of the supply

    • the charged particles in both wires move with the same average speed because the current in both wires is the same

    • the charged particles move faster through the wire with the larger diameter because there is a greater volume through which to flow

    • the charged particles move faster through the wire with the smaller diameter because it has a larger potential difference applied to it

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    51 mark

    A power cable X has resistance R and carries current I.

     A second cable Y has resistance 2R and carries current I over 2

     What is the ratio fraction numerator p o w e r space d i s s i p a t e d space i n space Y over denominator p o w e r space d i s s i p a t e d space i n space X end fraction  ?

    • 1 fourth

    • 1 half

    • 2

    • 4

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    61 mark

    A milliammeter shows a reading of 20 mA.

     How many electrons flow through the milliammeter in 10 seconds?

    • 0.20

    • 3.2 × 1020

    • 200

    • 1.3 × 1018

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    71 mark

    In a simple electrical circuit, the current in a resistor is measured as (2.50 ± 0.05) mA. The resistor is marked as having a value of 4.7Ω  ± 2 %.

     If these values were used to calculate the power dissipated in the resistor, what would be the percentage uncertainty in the value obtained?

    • 2 %

    • 4 %

    • 6 %

    • 8 %

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    81 mark

    A battery, with a constant internal resistance, is connected to a resistor of resistance 250 Ω, as shown.

    cie-ial-images430png

    The current in the resistor is 40 mA for a time of 60 s. During this time 6.0 J of energy is lost in the internal resistance.

     What is the energy supplied to the external resistor during the 60 s and the e.m.f of the battery ?

     

    Energy / J

    E. m. f / V

    A

    B

    C

    D

    2.4

    2.4

    24

    24

    2.4

    7.5

    10.0

    12.5

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      91 mark

      The current in the circuit shown is 4.8 A

      cie-ial-images431png

      What is the direction of flow and the rate of flow of electrons through the resistor R ?

       

      Direction of flow

      Rate of flow

      A

      B

      C

      D

      X to Y

      X to Y

      Y to X

      Y to X

      3.0 × 1019 s–1

      6.0 × 1018 s–1

      3.0 × 1019 s–1

      6.0 × 1018 s–1

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        101 mark

        The charge that an electric battery can deliver is specified in ampere-hours.

         For example, a battery of capacity 40 ampere-hours could supply, when fully charged, 0.2 A for 200 hours.

         What is the maximum energy that a fully charged 12 V, 40 ampere-hour battery could supply ?

        • 1.7 kJ

        • 29 kJ

        • 1.7 MJ

        • 29 MJ

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        11 mark

        Four point charges, each of charge Q, are placed on the edge of an insulating disc of radius r.

         The frequency of rotation of the disc is f.

        cie-ial-images432png

        What is the equivalent electric current at the edge of the disc ?

        •  4 Q f

        • fraction numerator 4 Q over denominator f end fraction

        • 8 πrQ space f

        • fraction numerator 2 Q f over denominator πr end fraction

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        21 mark

        The amount of energy transferred when 10 C of charge passes through a p. d. of 20 V is the same as the energy needed to raise a 2 kg mass through a distance x.

         Take gravitational field strength to be 10 N kg–1.

         What is the value of x?

        • 0.1 m

        • 1.0 m

        • 10 m

        • 100 m

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        31 mark

        The ratings of two lamps are as follows:

         

        X

        230 V, 100 W

        Y

        230 V, 60 W

         

        During normal operation, which of the lamps will have larger current and resistance?

        • I subscript X greater than I subscript Y space a n d space R subscript X greater than R subscript Y

        • I subscript X greater than I subscript Y space a n d space R subscript X less than R subscript Y

        • I subscript X less than I subscript Y space a n d space R subscript X greater than R subscript Y

        • I subscript X less than I subscript Y space a n d space R subscript X less than R subscript Y

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        41 mark

        A parallel beam of protons, each with charge e, travel at uniform velocity v. This results in current I being formed.

         What is the number of protons present in a unit length of the beam?

        • I over e

        • fraction numerator I over denominator e v end fraction

        • fraction numerator I space v over denominator e end fraction

        • I over v

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        51 mark

        The diagram shows a model of an atom in which two electrons move round a circular orbit. The electrons complete 1.0 × 1015 revolutions around the nucleus every second.

        cie-ial-images433png

        What is the current caused by the motion of the electrons in the orbit?

        • 1.6 × 10–34 A

        • 3.2 × 10–34 A

        • 1.6 × 10–4 A

        • 3.2 × 10–4 A

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        61 mark

        A slice of germanium of cross-sectional area 1.0 cm2 carries a current of 56 µA. The number density of charge carriers in the germanium is 2.0 × 1013 cm–3.

        cie-ial-images434png

         Each charge carrier has a charge equal to the charge on an electron.

        What is the average drift velocity of the charge carriers in the germanium?

        • 0.18 m s–1 

        • 18 m s–1

        • 180 m s–1

        • 1800 m s–1

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        71 mark

        I1 and I2 are currents flowing through two different circuits, as shown in the diagram below.

        cie-ial-images435png

        Calculate the difference in the total charge that flows through the two circuits in the first 7 seconds.

        • 0 C

        • 21 C

        • 42 C

        • 49 C

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        81 mark

        The Atlantic torpedo is a large electric fish capable of generating a voltage of 220 V between its tail and its head. This drives a pulse of current of 15 A lasting for a time of 2.0 ms. The fish produces 200 pulses per second.

         What is the average power output of the fish?

        • 33 W

        • 1.3 kW

        • 3.3 kW

        • 6.6 kW

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        91 mark

        A high potential is applied between the electrodes of an ionised gas. The gas carries a current of 8.16 mA and the number of electrons passing any point in the gas per unit time is 2.58 × 1016 s–1

         If the charge on each positive particle is 3.2 × 10–19 C, what is the number of positively charged particles passing any point in the gas per unit time?

        • 1.26 × 1016 s–1

        • 2.58 × 1016 s–1

        • 3.84 × 1016 s–1

        • 10.3 × 1016 s–1

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        101 mark

        An electron beam of current 50 μA flows in a cathode-ray oscilloscope. The time-base causes the beam to sweep horizontally across the screen at 1.0 × 104 cm s–1  

         What is the number of electrons arriving at the screen in one centimetre length of the horizontal trace?

        • 3.1 × 1010

        • 3.1 × 1013

        • 1.3 × 1013

        • 8.0 × 1014

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