PHYSICS

JAMB 2007 - Question 21

Physics 2007 JAMB Past Questions - Question 21: 118:8 cm² surface of the copper cathode of a voltmeter is to be coated with 10-m thick copper of density 9 x 10³kgm-³. How long will the process run with 10 A constant current? A. e.c.e. of copper = 3.3 x 10-kgm-³

Choose the correct answers from the options given.
118:8 cm² surface of the copper cathode of a voltmeter is to be coated with 10-m thick copper of density 9 x 10³kgm-³. How long will the process run with 10 A constant current? A. e.c.e. of copper = 3.3 x 10-kgm-³
A:
B:
C:
D:
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Correct Answer

C

Explanation

But mass, M = volume x density
and volume = cross sectional area x thickness
M = 118.8cm^2 x 10^-6 x 9 x 10^3
∴ 118.8cm^2 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 = 118.8×9/3.3
t = 324 seconds
Convert to minutes by dividing by 60
t = 324/60

t = 5.4 sec