(a)(i) Name and explain the common defects of a primary cell.
(ii) State two advantages of a secondary cell over a primary cell.
(b) Draw a labelled diagram to show the essential parts of a dry leclanche cell.
(c)(i) Explain why six accumulators each of e.m.f 2V connected in series can be used to start the engine of a car whereas eight dry cells each of e.m.f 1.5 V connected in series cannot be used.
(ii) Name the materials used for the positive terminal, the negative terminal and the electrolyte in a
I. leclanche cell;
II. charged lead acid accumulator.
Verified Correct Answer: .
Physical Principles & Numerical Solution
(a)(i) Primary cell defects:
— Polarization
— Local action Polarization
— This is due to hydrogen bubbles covering the positive electrode (copper plate). Local action
— This is due to the use of impure zinc or the gradual wearing away of the negative electrode zinc plate.
(ii) Advantages of secondary cell over a primary cell:
— a secondary cell can be recharged while primary cell cannot.
— secondary cell can supply current for a longer period while the primary cell has a short life-span.
(b)
(c)(i) The internal resistance of the dry cells is much larger than that of the accumulators, hence accumulators will produce larger currents needed to start the engine.
(ii)
Positive terminal
Negative terminal
Electrolyte
Leclanche cell
Carbon rod
Zinc rod
Ammonium chloride (NH\(_4\)
charged lead acid accumulator
Lead (IV) oxide or Lead peroxide
Lead
Lead Tetra oxo-sulphate (VI) acid (H\(_2\)SO\(_4\))
Source: Myschool Past Questions Archive (Record #53738)