JAMB - Physics (2007 - No. 37)
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]
[3.3 x 10-7kgC-1]
5.4 min
10.8 min
15.0 min
20.0 min
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.
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.
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