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118.8cm2 surface of the copper cathode of a voltameter is to be coated with 10-6m...

Physics
JAMB 2007

118.8cm2 surface of the copper cathode of a voltameter is to be coated with 10-6m thick copper of density 9 x 103kgm-3. How long will the process run with 10A constant current?
[3.3 x 10-7kgC-1]

  • A. 5.4 min
  • B. 10.8 min
  • C. 15.0 min
  • D. 20.0 min
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Correct Answer: Option A
Explanation

From faradays law, M = itz
But mass, M = volume x density
and volume = cross-sectional area x thickness
M = 118.8 x 10\(^{-6}\) x 9 x 10\(^3\)
∴ 118.8cm2 x 10\(^{-6}\) x 9 x 10\(^3\) = 10 x t x 3.3 x 10\(^{-7}\)
∴ (118.8 x 9) x 10\(^{-7}\) = 10 x t x 3.3 x 10\(^{-7}\)

∴ t = \(\frac{118.8 \times 9}{ 3.3}\)

t = 324 seconds

Convert to minutes by dividing by 60

t = \(\frac{324}{60}\)

t = 5.4 mins.

There is an explanation video available below.


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