Domestic Wiring and Illumination Questions and Answers

Answer: B

Cleat wiring is the quickest and the cheapest system to put up and to take down, since the wires are held in porcelain cleats fixed to the wall or ceiling, and the material can be used again. This makes it the most suitable for temporary installations, such as at fairs and functions. Conduit wiring is a permanent and costly system, batten wiring and wood casing wiring are also fixed and are used in permanent work. The answer is cleat wiring, option (B).

Answer: B

Lighting systems are classified by the share of the light sent downward and upward: direct lighting sends 90 to 100 percent downward, semi-direct sends 60 to 90 percent downward, general diffused sends about equal amounts both ways, semi-indirect sends 60 to 90 percent upward, and indirect sends 90 to 100 percent upward. A system with 30 percent downward and 70 percent upward is therefore semi-indirect, option (B). The quantity is the upward light output divided by the total, and 70 percent upward is between the semi-indirect limits of 60 and 90 percent.

Answer: D

A geyser is a water heater, and its purpose is to keep the heat in the water. The space between the outer casing and the inner tank is therefore filled with a heat insulating material, such as glass wool, so that little heat is lost to the surroundings and the water stays hot. A material of high heat conduction would carry the heat away, and high electric conductivity and high magnetic permeability have no use in the filling. The answer is heat insulation, option (D).

Answer: D

A ratchet brace holds a bit and is turned by hand with a ratchet action, so it can be used to drill holes in wooden blocks even where there is little room to turn it a full circle, since the handle can be moved to and fro. A spanner is used to turn nuts and bolts, a hacksaw cuts metal and pincers grip or pull out nails and wire. So the tool for drilling holes in wood is the ratchet brace, option (D). The bit is held in the chuck of the brace and the sweep of the handle gives the turning force, so the worker can bore holes of a fairly large size in wood by hand.

Answer: C

The try square is the tool used to check the squareness of a job, that is, whether two surfaces meet at 90 degrees, and to mark lines at right angles. A staggered square is not a measuring tool, a jenny (odd-leg) caliper scribes lines parallel to an edge and does not check a right angle, and a spring joint square is not a tool at all in this sense. The answer is Try square, option (C). It has a stock and a blade fixed at 90 degrees to each other, and when the stock is held against one edge of a job the blade shows whether the adjoining surface is square.

Answer: A

When two wires are to be tapped from a main wire at the same time, the joint used is the duplex cross tap joint, in which two tap wires are joined to the main wire at one place. An aerial tap joint is used on overhead lines, a Western union joint is a straight joint between two wires, and the Britannia tee joint is a tee joint of a single branch. So the answer is Duplex cross tap joint, option (A). A tap joint of this kind is used in conduit and cleat wiring to supply two branches from one place on the main wire, and the joint is taped to insulate it.

Answer: C

The rivet in the figure has a head shaped like a half-sphere, a dome, on a cylindrical shank, and the head sits above the surface of the plate. This is the round head rivet, also called the snap head or button head rivet. A flat head rivet has a flat top, a countersunk rivet has a conical head that sinks flush into the plate, and a tinman's rivet is a small rivet with a thin flat head used in sheet metal work. The answer is Round head rivet, option (C).

Answer: C

In decorative lighting a bimetallic flashing unit has a bimetallic strip that bends when heated by the current and then opens or closes a contact, and so makes and breaks the circuit again and again. It therefore acts as a switch for the other lamps, which flash on and off. It is not an emergency lamp, it does not limit the current to a safe value, and it does not give a voltage boost. The answer is act as a switch for other lamps, option (C).

Answer: C

The stroboscopic effect is the apparent slowing or standing still of a rotating machine seen under a lamp that flickers at the supply frequency, since the light of a fluorescent lamp falls to zero twice in each cycle. It is prevented by the twin tube arrangement, in which two tubes are run with their currents out of phase, one with a capacitor, so that the dips in the light of one tube are filled by the other. Connecting adjacent points to the same phase would add to the flicker, and a colour filter or a stabiliser does not remove it. The answer is option (C).

Answer: B

The recommended cutting speed for drilling depends on the material being drilled. For thermo-setting plastic, the key gives a cutting speed of 20 to 30 metres per minute, option (B). A speed of 5 to 8 m/min is used for harder metals, and the higher speeds of 40 to 50 and 70 to 100 m/min would overheat the plastic and the drill, and burn or crack the material. The key is followed for this recall item. Plastics are drilled at moderate speeds with sharp drills, and the thermo-setting kinds are hard and brittle, so too high a speed would burn and crack the material.