Answered past questions on electrical maintenance and repair (EEC 226)

Mention four (4) changes that occur during the discharging of a battery (4 marks)
1. Color of both plates is changed. Positive plates become light brown and negative plates become light grey.
2. Specific gravity of acid decreases from 2.3 to 1.8v
3. Voltage of each cell decreases from 2.3 to 1.8v
4. The cell gives out energy.

Explain the term “solder”
Solder: solder is a metal mixture used to connect metal parts of components. A mixture of 60% tin and 40% lead is known as 60/40 solder.

Mention three (3) possible faults in an electric immersion heater. (3 marks)
1. Elements end may touch the corner of the metal tube short circuit and earth faults.

2. Broken supply cord terminals or wire in the plug top ( i.e discontinuity also called open circuit)
3. Burnt circuit — open circuit.

What are the four (4) precautions to be taken when soldering components to a PCB? (4 marks)
1. Never touch the element of the soldering iron at 400⁰c
2. Hold the wires to be heated with tweezers or clamp’s
3. Hold the cleaning sponge wet during use
4. Always return the soldering iron to it’s stand when not in use. Never put it down on the workbench.

Explain the use of heat sink. (1½ mark)
A heat sink is a better conductor of heat than the electrical part, so it will pick up the heat and stop it from going to the components.

Explain dry joint and it’s cause.
Dry joints: These are badly soldered joints
Cause: Due to high resistance

Mention three (3) types of electric stove (heaters). (3 marks)
1. Open coil type: ordinary table heaters made of low range coiled nichrome elements are used.
2. Solid plate type: heater element isn’t visible it takes much time to become hot and cool down.
3. Tube type: triangular shaped heating units are used. Nichrome wire, insulated wire, powder of magnesium oxide is fitted in the tube.

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