Domestic Wiring and Illumination Questions and Answers

Answer: C

The regulations require one ring circuit for every 100 m² of floor area or part of it. A ring final circuit feeds socket outlets and one ring is allowed to serve a limited area so that the load is spread.

The figures 10 m², 50 m² and 1000 m² are not the limit in the regulations. A limit of 10 m² would need far too many rings and 1000 m² would overload one ring. So the third option is correct.

Answer: C

The choke required is rated 40 W. When two tubes are connected in series with one choke, the choke has to carry the current for both tubes, and its rating is the sum of the tube wattages, 20 W + 20 W = 40 W.

A choke of 10 W or 20 W would be too small for the tubes in series, and 80 W would be double what is needed. So the third option is correct. The choke limits the current through the tubes and, with the starter, gives the voltage pulse that lights them, so its rating has to suit the tubes it serves.

Answer: A

The key gives about 80 % as the reduction in the life of a fluorescent tube on DC operation compared with AC. On DC the mercury and the ions move towards one electrode, so one end of the tube darkens and wears faster, which shortens the life of the tube.

I could not confirm the exact percentage from a source, and some books give a smaller reduction, so the figure rests on the key. The first option is the answer given.

Answer: B

The wrong pair is the sodium vapour lamp as a night lamp. Sodium vapour lamps give a yellow light and are used for street and highway lighting, where their high efficiency matters, not as a small night lamp in a room.

The other pairs are right: the carbon arc lamp as a cinema projector lamp, the neon discharge lamp as an indicator lamp, and the mercury vapour lamp for industrial lighting. So the second option is the answer.

Answer: B

In a microwave oven, cooking is done with microwave energy of 2450 MHz frequency, that is 2.45 GHz. At this frequency the water molecules in the food absorb the energy and heat up.

The options of 2450 GHz, 2450 kHz and 2450 Hz are off by factors of a thousand or more: 2450 GHz would be in the terahertz range, and 2450 kHz and 2450 Hz are radio and audio frequencies. So the second option is the answer.

Answer: D

A sole plate is not a part of an electric bell. It is a part of an electric iron, the flat plate that is heated and pressed on the clothes.

An electric bell has an electromagnet, an armature that is pulled by it, a hammer fixed to the armature, a gong that is struck and a contact screw that breaks the circuit to make the armature vibrate. So the fourth option is the answer.

Answer: C

The key gives 1 MΩ as the minimum acceptable insulation resistance of a food mixer. An appliance with a metal body and a motor must have a high insulation resistance between the live parts and the body to prevent a shock, and a megohm is the usual order of the minimum value for such appliances.

I could not check the exact figure in a standard, so the answer follows the key. Values of 10 Ω, 100 Ω and 1 kΩ are far too low to be safe for insulation. The third option is the answer.

Answer: A

High capital cost is not a characteristic of cleat wiring. Cleat wiring is a cheap and temporary system in which the wires are held in porcelain cleats, and it is quick to put up and take down.

The other statements are its characteristics: faults are easy to find because the wires are in the open, it is easy to repair, and it is used for temporary purposes such as a wedding or building work. So the first option is the answer.

Answer: B

The BIS symbol shown, a box with a hatched strip, stands for a distribution fuse board with switches. The figure is a rectangle that contains a hatched strip.

I could not check the symbol in the Bureau of Indian Standards drawing sheet, so the answer follows the key. The options 'without switches' and 'main fuse board' are the other symbols of the set. The second option is the one given.

Answer: A

The key gives a godown (storage room) lighting system for the diagram. In the diagram four lamps L1 to L4 are fed from the phase and neutral through a chain of switches, with S1 a one-way switch and S2, S3 and S4 two-way switches.

I could not check this against a textbook drawing, so the answer follows the key. A staircase or corridor system uses two-way switches for the same lamp or lamps from two ends, and a garden system uses outdoor fittings. The first option is the answer given.