Class 7 Science Chapter 10 MCQ

An extremely large current can flow in household electric wiring circuit under two circumstances short circuit and overloading. Short circuit is the touching of live wire and neutral wire directly is known as short circuit. And second is when house or some other building is wired, the wiring is protected by fuses. When a short circuit or overloading occurs the flow of current increase heavily, the fuse wire blows out cutting off the “Electric Supply”.

The electric bulb has very thin filament of tungsten metal. The filament of an electric bulb has a high resistance. When electric current passes through the very thin, high resistance filament of an electric bulb, heat is produced in it. Due to this the filament of electric bulb gets heated to a very high temperature and starts glowing.

Here are all the statements are correct. Hence your answer will be option [D].

The electric heating appliances (such as electric room heater, electric iron etc.) works on the heating effect of electric current. All the electric heating appliances contains coils of high resistance wire, made of nichrome alloy. A lot of heat is produced in the heating element because it is made of high resistance nichrome-wire and negligible heat is produced in the connecting wires of copper because copper has very low resistance.

Portable generators as well as inverters has very high voltage of 220 volts.

A fuse is a safety device which prevents electric fires and damage to electrical appliances due to excessive flow of current. A fuse works on the heating effect of current. A fuse consists a short length of a thin, tin-plated copper wire having low melting point. If due to some reason the current in household wiring suddenly becomes too large or exceeds the safe limit, then the fuse will blow off or cut or melt (its wire will be we get heated to much, melt and break the circuit). When the fuse wire breaks, electricity supply in the household wiring is automatically cut off before any damage can be done to the rest of wiring or to the electrical appliances being used.

Here are all the statements are correct. Hence your answer will be option [D].

The symbol for representing a battery for three cells will have three pairs of long and short parallel lines connected to one another.

MCB stand for miniature circuit breaker. These days MCBs or miniature circuit breakers are being used increasingly in household electric wiring, in place of traditional fuses. MCB does not work on the heating effect of current. MCB works on the magnetic effect of current.

All the bulbs will glow simultaneously because there is no time lag in the flow of current as soon as the circuit is complete.

Here all the statements are correct. Hence your answer will be option [D].

MCB stand for miniature circuit breaker. These days MCBs or miniature circuit breakers are being used increasingly in household electric wiring, in place of traditional fuses. MCB does not work on the heating effect of current. MCB works on the magnetic effect of current.

The magnetic effect of current was discovered by scientist named “Hans Christian Oersted”. When electric current passes through a wire, the current-carrying wire behaves like a magnet. It is this magnetic field produced by the current carrying wire which exerts of force on the compass needle and deflects it.

MCB stand for miniature circuit breaker. These days MCBs or miniature circuit breakers are being used increasingly in household electric wiring, in place of traditional fuses. MCB does not work on the heating effect of current. MCB works on the magnetic effect of current.

The fluorescent tube lights and compact fluorescent lamps do not have filaments. Fluorescent tube lights and compact fluorescent lamps do not work on the heating effect of current. The fluorescent tube light on lamp contains mercury vapor, which is a kind of gas.

An electrical fuse is a safety device in the circuit that protects electrical appliances and systems by breaking the connections when a short circuit is occurring. The fuse wire is made up of Sn (tin) and Pb (lead) alloy because of its high resistance and low melting point.

Generally, electric current can produce three effects which are heating effect, magnetic effect and chemical effect.

A fluorescent tube light a lamp contains mercury vapor. The inside of glass tube is coated with an opaque, white material called “phosphor”. When a fluorescent tube light is switch on and current passes through it, the mercury vapor emits invisible ultraviolet radiations. The phosphor absorbs this ultraviolet radiations and glows to emit white light. Though fluorescent tube lights and CFLs are initially more expensive to buy but there a running cost is much less because they consume much less electricity and they also last much longer.

Here all the statements are correct. Hence your answer will be option [D].

Here all the statements are correct. Hence your answer will be option [D].

Here all the statements are correct. Hence your answer will be option [D].

Here all the statements are correct. Hence your answer will be option [D].

Steel is not used for making electromagnets because when current is switched off from the coil of an electromagnet made of a steel pieces, it does not lose all its magnetic. The still remains the magnetism and becomes a permanent magnet.

Here all the statements are correct. Hence your answer will be option [D].

For using electric gadgets or appliances or circuit, we have to turn the switch in ON position. Therefore, precautions given in option [D], need not to be considered.