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”.

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

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

The electric bulb or electric lamp which we use for producing light works on the heating effect of electric current. An electric bulb is basically used for producing light but it also gives out heat. In fact, a major part of the electricity consumed by the filament of an electric bulb is converted into heat (due to which the bulb becomes hot), only a small part of electricity is converted into light.

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

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.

The heating elements of most of the electric heating appliances such as, electric iron, electric kettle, electric geyser, electric oven, hot plates and hair dryer etc., cannot be seen by us because they are concealed inside the body of these appliances.

In case of electric fuse, there is only a maximum limit on the current which can safely flow in the electric circuit.

Electromagnets are used in the construction of a large number of devices like electric bells, loudspeakers, electric motors etc. The electric bell works on the magnetic effect of current. Electromagnet attract the iron armature and the clapper strikes the gong which producing a ringing sound.

We use a thin wire in a fuse because it has a much greater resistance than the rest of connecting wires. When a fuse gets blown or breaks a new fuse has to be fitted in its place to restore the electricity supply in the household circuit. We should not use a thick wire as a fuse wire because it will have a low resistance and then it will not get heated to its melting point easily.

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.

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.

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

When the switch is in off position, circuit is incomplete. It is said to be open and therefore, no current flows through it.

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.

The electric bell works on the magnetic effect of current, not the heating effect of current.

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.