Question

14. (a) Explain briefly the purpose of earthing an electrical appliance.
(b) An electric current passing through an electrolyte for 2 minutes deposited 200g of a substance. If the electrochemical equivalent of the substance is 8.33×10⁻⁴gC⁻¹, calculate the current that passed.

Accepted Answer

(a) Earthing an electrical appliance provides a low-resistance path to the ground for any fault current (e.g. from a short circuit where the live wire touches the metal casing of the appliance). This ensures that a large current flows to earth instead of through a person touching the appliance, protecting them from electric shock, and it also causes a fuse or circuit breaker to trip quickly, disconnecting the faulty appliance from the supply.

(b) m = zIt, so I = m/(zt) = 200/(8.33×10⁻⁴×120) ≈ 2000A (as computed in Q4(b) above, using the same given figures).

WAEC Physics 2012 Theory — Question 14

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