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A Levels Physics (9702)•9702/14/M/J/25
Question 29 from 9702/14/M/J/25

Explanation

Calculate electrons using current, charge, and electron charge

Steps:

  • Current I = V/R = 6 V / 10 Ω = 0.6 A
  • Time t = 24 hours = 24 × 3600 = 86400 s
  • Total charge Q = I × t = 0.6 A × 86400 s = 51840 C
  • Number of electrons N = Q / e = 51840 / (1.6 × 10^{-19} C) ≈ 3.24 × 10^{23}

Why D is correct:

  • Matches N ≈ 3.2 × 10^{23} from Q = It and N = Q/e, where e is elementary charge.

Why the others are wrong:

  • A: Underestimates by factor of 10^{23}, likely missing time conversion or e.
  • B: Too small, ignores full Q or uses wrong units for t.
  • C: Overestimates by factor of 10, possibly dividing by 1.6 × 10^{-20} instead of 10^{-19}.

Final answer: D

Topic: Electric current

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