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Q1. What are the causes of short circuiting and overloading?

Solution

The short circuiting may occur due to the touching of live wire and neutral wire directly. Overloading may be due to the flow of excessive current when many devices are connected to a single socket.

Q2. Who first noticed the deflection of compass needle due to current carrying wire?

Solution

The scientist named 'Hans Christan Oersted' noticed the deflection of compass needle when the current passed through the wire.

Q3. How a fuse wire prevents damages to electrical circuits and possible fires?

Solution

There is a maximum limit for the current to flow through the circuit. If accidentally, the current exceeds the safe limit, the wire may become overheated and may cause fire. In this case, the fuse wire blows off and breaks the circuit thus prevents the damages to electrical circuit.

Q4. What is a circuit diagram? What is its use?

Solution

A diagram which tells us how the various components in a circuit have been connected by using the electrical symbols of the components, is called a circuit diagram. We usually represent an electric circuit by its circuit diagram because it is much easier to draw a circuit diagram by using symbols.

Q5. Give two advantages of electromagnets over permanent magnets.

Solution

1. The magnetism of an electromagnet can be switched on or switched off as desired. This is not possible with a permanent magnet. 2. An electromagnet can be made very strong by increasing the number of turns in the coil, and by increasing the current passing through the coil. On the other hand, a permanent magnet cannot be made so strong.

Q6. Why is it that same current flowing through the tungsten filament of an electric bulb produces enormous heat but almost negligible heat is produced in the connecting wires of the bulb?

Solution

This is because of the fact that the fine tungsten filament has a very high resistance whereas copper connecting wires have very low resistance.

Q7. What is the characteristic of fuse wire?

Solution

Fuse wire should have low melting point and high resistance.

Q8. Give two advantages of CFLs.

Solution

Two advantages of CFLs are: (i) CFLs do not have filaments and do not work on  heating effect of current. So, they do not waste electricity by producing heat. (ii) CFLs can be fixed in ordinary bulb holders which are used for traditional, filament-type electric bulbs.

Q9. Some electrical appliances have elements in them. How do you notice that they have become hot?

Solution

Some electrical appliances have elements in them. When they are switched on after connecting to the electric supply their elements becomes red hot and give out heat.

Q10. What happens when a large amount of current passes through a wire?

Solution

If large amount of current passes through a wire, the wire may become so hot that it may even melt and break.

Q11. What happens when the bulb gets fused?

Solution

When the bulb gets fused, its filament breaks and it does not glow.

Q12. What do you mean by an electromagnet?

Solution

Electromagnet is a temporary magnet which behaves like a magnet only when electric current flows through it. When the electric current is switched off it looses its magnetism.

Q13. If the filament of the bulb is broken, would the circuit be complete? Would the bulb still glow?

Solution

If the filament of the bulb is broken then the circuit would be incomplete and the bulb will not glow.

Q14. What do you observe if the electric bulb remains switch 'ON' for a long period?

Solution

The temperature of the electric bulb will be raised and it becomes hot.

Q15. What is the function of needle in a magnetic compass?

Solution

The needle in a magnetic compass is a tiny magnet which points in the north-south direction.

Q16. Give two uses of electromagnets.

Solution

Two uses of electromagnets are:

• Electromagnets are used in the construction of a large number of devices like electric bells, loudspeakers, electric motors, electric fans, etc.
• Electromagnets are used by doctors to remove tiny iron pieces from the eyes of a person (which may have fallen into the eyes accidently).

Q17. What is a battery? Give some examples of devices where battery is used.

Solution

A combination of two or more cells is called a battery. Some devices which use battery are - torches, transistors, toys and TV remote controls.

Q18. What is the magnetic effect of electric current?

Solution

When electric current passes through a wire, it behaves like a magnet. This is called magnetic effect of electric current.

Q19. What is the usual name of magnets whose magnetism can be turned on or off as desired?

Solution

The magnets whose magnetism can be turned on or off when desired are called electromagnets.

Q20. Describe an activity to make an electromagnet.

Solution

(i) Take a long piece of insulated wire and an iron nail. (ii) Wind the wire tightly around the nail. (iii) Connect the free ends of the wire to the terminals of a cell through a switch. (iv) Place some pins on or near the end of the nail and switch on the current. The pins cling to the tip of the nail. (v) The coil behaves like a magnet till the current flows through it.

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