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ASPhysicsCIEExam Questions9. Electricity9.1 Electric Current

Electric Current (CIE AS Physics)

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9.1 Electric Current

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9.1 Electric Current

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1
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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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2
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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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3
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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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4
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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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5
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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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6
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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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1
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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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2
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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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3
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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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    4
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    A wire with a resistance of 2.0 Ω has 8.2 × 1028 electrons pass through it at an average drift speed of 0.09 mm s-1. The potential difference of the resistor is 12 V.

    What is the cross-sectional area of the wire?

    • 5.1 µm2

    • 0.14 mm2

    • 5.1 mm2

    • 0.14 cm2

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    5
    Sme Calculator    1 mark

    A 3.0 Ω resistor has 7.5 × 1018 electrons pass through it in 5.0 s.

    What is the potential difference and charge of the resistor?

     

    Charge / C

    Potential difference / V

    A.

    1.2

    0.24

    B.

    1.2

    0.72

    C.

    12

    2.4

    D.

    12

    7.2

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      1
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      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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      2
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      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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      3
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      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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      4
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      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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      5
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      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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      6
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      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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      7
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      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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      8
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      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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