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Cambridge International AS & A Level · 9 · structured

Track charge and energy through a component

Track charge and energy through a component · Original GioPhysics question with a detailed, mark-by-mark answer guide.

Demand
demanding
Marks
14
Topics
5
Answer
Complete
structured14 marks

A steady current0.250mA passes through a component for2.00min. During this interval0.180 J is transferred in the component. Use e=1.60×10⁻¹⁹C.

  1. (a)

    Explain quantisation of isolated macroscopic charge. Which magnitudes,4.80×10⁻¹⁹C and4.00×10⁻¹⁹C, can arise by gaining or losing whole electrons? State the electron's charge.

    3 marks
  2. (b)

    Find total charge passing through the component and the number of electrons corresponding to its magnitude.

    3 marks
  3. (c)

    Define potential difference across the component and state the meaning of 1volt.

    2 marks
  4. (d)

    Calculate the component p.d. and the energy transferred when2.00 C passes at that same p.d.

    3 marks
  5. (e)

    State what electric current is in terms of charge carriers. Explain why random carrier motion alone does not give a steady net current, and state the conventional-current direction for drifting electrons.

    3 marks
Ready to self-mark?Reveal the detailed answer guide
Answer overview(a) Macroscopic charge changes in integer multiples of e.4.80×10⁻¹⁹C=3e is possible;4.00×10⁻¹⁹C=2.5e is not by whole-electron transfer. Electron charge−1.60×10⁻¹⁹C. (b) Q=0.250×10⁻³×120=0.0300 C; N=0.0300/e=1.875×10¹⁷≈1.88×10¹⁷. (c) Potential difference is energy transferred per unit charge between two points;1 V=1 J C⁻¹. (d) V=W/Q=0.180/0.0300=6.00 V; W=QV=2.00×6.00=12.0 J. (e) Electric current is net flow of charge carriers. Random motion in opposite directions cancels on average; a directed drift produces net transport. Conventional current is opposite electron drift.
01

(a)

3 marks

Explain quantisation of isolated macroscopic charge. Which magnitudes,4.80×10⁻¹⁹C and4.00×10⁻¹⁹C, can arise by gaining or losing whole electrons? State the electron's charge.

How to approach it

Identify what the question is testing, organise the response into distinct mark-earning points, and make every conclusion traceable to a physical principle or to the evidence supplied.

  1. 1

    Divide each charge magnitude by e.

  2. 2

    Require an integer electron count in the stated context.

  3. 3

    Give negative electron charge, distinguishing sign from magnitude.

02

(b)

3 marks

Find total charge passing through the component and the number of electrons corresponding to its magnitude.

How to approach it

List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.

  1. 1

    Convert current to amperes and2min to 120s.

  2. 2

    ApplyQ=It.

  3. 3

    Divide charge magnitude by elementary charge for carrier count.

03

(c)

2 marks

Define potential difference across the component and state the meaning of 1volt.

How to approach it

Identify what the question is testing, organise the response into distinct mark-earning points, and make every conclusion traceable to a physical principle or to the evidence supplied.

  1. 1

    Mention transferred energy and per unit charge.

  2. 2

    Give the joule-per-coulomb equivalence.

04

(d)

3 marks

Calculate the component p.d. and the energy transferred when2.00 C passes at that same p.d.

How to approach it

List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.

  1. 1

    Use the charge found in(b).

  2. 2

    Rearrange energy/charge relation for6.00 V.

  3. 3

    UseW=QV for12.0 J.

05

(e)

3 marks

State what electric current is in terms of charge carriers. Explain why random carrier motion alone does not give a steady net current, and state the conventional-current direction for drifting electrons.

How to approach it

Identify what the question is testing, organise the response into distinct mark-earning points, and make every conclusion traceable to a physical principle or to the evidence supplied.

  1. 1

    State charge-carrier flow/net transport.

  2. 2

    Explain cancellation of random directions and need for a mean drift.

  3. 3

    Give conventional direction opposite negative-electron motion.

Complete marking guidance

Use these worked steps alongside the part-by-part answers. They explain the method and mark allocation; they do not add extra marks.

  1. (a) Divide each charge magnitude by e.
  2. (a) Require an integer electron count in the stated context.
  3. (a) Give negative electron charge, distinguishing sign from magnitude.
  4. (b) Convert current to amperes and2min to 120s.
  5. (b) ApplyQ=It.
  6. (b) Divide charge magnitude by elementary charge for carrier count.
  7. (c) Mention transferred energy and per unit charge.
  8. (c) Give the joule-per-coulomb equivalence.
  9. (d) Use the charge found in(b).
  10. (d) Rearrange energy/charge relation for6.00 V.
  11. (d) UseW=QV for12.0 J.
  12. (e) State charge-carrier flow/net transport.
  13. (e) Explain cancellation of random directions and need for a mean drift.
  14. (e) Give conventional direction opposite negative-electron motion.

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