(a) Define:(i) the coulomb; (ii) resistance.
(b) State the three effects of an electric current.
(c) State the standard international colour convention for the insulating material covering the following electrical wires in a three-pin plug: (i) live; (ii) neutral; (iii) earth.
(d)
A water melon of mass 5.0 kg is suspended on a uniform rod of mass 4.0 kg and 4.0 in long as illustrated in the diagram above. If the rod is in equilibrium by the action of the force between the charges +q and -q, calculate the:
(i) anti-clockwise moment;
(ii) value of q. [ g = 10 ms\(^{-2}\)]
Explanation
(a)(i) The coulomb is defined as the quantity of electric charge passing through a point in a conductor when a steady current of one ampere passes for one second.
(ii) Resistance is the opposition offered to the flow or passage of an electric current in a conductor.
(b) The effects of electric current are:
(i) Magnetic (ii) Chemical
(iii) Heating or thermal.
(c) The standard international colour for insulating cover for a three in plug are:
(i) Live is brown or red colour.
(ii) Neutral is blue or black colour.
(iii) Earth is green/yellow/green and yellow colour.
(d) Clock wise moment = 4gl\(_2\) + \(\frac{kq^2l_3}{12}\)
\(\frac{4 \times 10 \times 1 + 8.99 \times 10^9 \times q^2 \times 3}{(2.5)^2}\) = 40 + 4.315 x 10\(^{9}\) x \(q^{2}\)
Anti-clockwise moment = 5gl\(_1\) = 5 x 10 x 1 = 50 Nm
But sum of clockwise moment = Anti-clockwise moment 40 + 4.315 x 10\(^9\) q\(^2\) = 50
q = \(\sqrt{\frac{10}{4.315 \times 10^9}}\)
= 4.814 x 10\(^{-5}\)C