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

### Question

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

### Explanation:

From faradays law, M = itz
But mass, M = volume x density
and volume = cross sectional area x thickness
M = 118.8cm2 x 10-6 x 9 x 103
∴ 118.8cm2 x 10-6 x 9 x 103 = 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 sec

## Dicussion (1)

• From faradays law, M = itz
But mass, M = volume x density
and volume = cross sectional area x thickness
M = 118.8cm2 x 10-6 x 9 x 103
∴ 118.8cm2 x 10-6 x 9 x 103 = 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 sec