Question 3
-
(i) State four precautions to be taken in charging a battery. [4 marks]
(ii) Give two differences between primary and secondary cells [2 marks]
(iii) Explain briefly how a damaged socket can be replaced. [4 marks] - (i) List four types of measuring instrument used in an electrical workshop. [4 marks]
(ii) State one use of any of the instruments listed in 3b (i). [1 mark]
(iii) Explain briefly how electric current can be measured in a circuit. -
Sketch the British Standard (BS) graphical symbols for the following devices:
(i) fixed resistor;
(ii) a.c. motor;
(iii) fuse;
(iv) variable inductor;
(v) electric bell.
Observation
 Majority of the candidates that answered the questions performed very well.
In part (a), majority of the candidates stated the precautions to be taken in charging a battery.
Candidates gave two differences between primary and secondary cells
In part (b), candidates listed types of measuring instruments used in an electrical workshop. They equally stated the use of any of the listed instruments.
In part (c), majority of the candidates could sketch the graphical symbols for the listed devices.
The expected answers are:
(i)PRECAUTIONS IN CHARGING A BATTERY
- the battery charging room must be well ventilated
- ensure correct polarity of battery
- always add acid to water ( not water to acid )
- protective clothing / hand gloves should be used
- vent plugs must be removed before charging
- metals in the charging room should be painted to avoid corrosion
- no naked light (of any form) should be allowed in the charging room
- ordinary tap water should not be used for topping up the battery
- switch off charger before fixing the battery(ii)DIFFERENCES BETWEEN PRIMARY AND SECONDARY CELLS
(iii) REPLACEMENT OF A DAMAGED SOCKET
switch off / cut off supplyremove / unscrew the damage socketconnect a new socket with the live connected to the live, neutral to neutral and earth to earthscrew the new socket firmly and turn on the supply-
(i) TYPES OF A MEASURING INSTRUMENT
- ammeter
- voltmeter
- ohmmeter
- tachometer
- photometer - micrometer screw gauge / standard wire gauge
- hydrometer
- multimeter
- watt meter
- megger
- tape rule / measuring tape / ruler
- wheatstone bridge
- potentiometer
- verniercalipers(ii)USES OF MEASURING INSTRUMENTS
ammeter - used for measuring current
hydrometer - used for measuring specific gravity of electrolytes
voltmeter - used for measuring voltage
multimeter - used for measuring current/voltage/resista
ohmmeter - used for measuring resistance
tachometer - used for measuring speed of rotation
megger - used for measuring very high resistance
photometer - used for measuring illumination
measuring tape/ruler/tape rule - used for measuring length / breadth / distance micrometer screw gauge
standard wire guage - used for measuring diameter of wires
wheatstonebrigde - measuring resistance
potentiometer - measuring voltage
vernier callipers - used for measuring diameter of wires(iii)MEASURING ELECTRIC CURRENT IN A CIRCUIT
identify the component terminal to be measured (1) break/open the circuit (1) insert an ammeter in series/ in line with the circuit (1) to the meter’s two points of break(1)and select the correct range (1) - BS GRAPHICAL SYMBOLS
