18. Explain the following.
(A) Why is the tungsten used almost exclusively for filament of electric lamps?
(b) Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?
(c)Why is the series arrangement not used for domestic circuits?
(d) How does the resistance of a wire vary with its area of cross-section?
(e) Why are copper and aluminium wires usually employed for electricity transmission?
Answers
Answer:
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Explanation:
a) Tungsten metal is used exclusively for making the filament of electric bulbs because it has a very high melting point. Due to its high melting point, the tungsten filament can be kept white hot without melting away.
b) Conductor of electric heating devices such as toaster or electric iron is made of an alloy rather than pure metal because if electric heating devices are made up of pure metal then the metal melt easily when heat is increase and pure metal get corrode easily.
c) When appliances are connected in series, the damage of one of the appliances can disconnect the whole circuit, which means the circuit would stop conducting current.
d) It is inversely proportional to the area of cross section of the wire. The more the area of cross section of the wire,the less is the resistance and the less the area,the more is the resistance.
e) Copper and aluminium are good conductors of electricity. They have very low resistance and allow the current to flow through them easily. Hence, they are used to make wires for electrical transmissions.
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ExplanatioN :-
Q)Why is the tungsten used almost exclusively for filament of electric lamps?
A:- Tungsten has a high melting point.Due to its high melting point,it does'nt melt even at high temperatures.And the electric lamp heats up with time as they are being used.Therefore,the tungsten filament can be kept hot without melting away.
Q)Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?
A:- In electric heating devices,the heat increases with time as they are being used.Pure metal would easily metal and corrode.Whereas,an alloy has high melting point and has high resistivity than that of a pure metal.Hence,it doesnt melt away or corrode.This is why we prefer alloy rather than a pure metal.
Q) Why is the series arrangement not used for domestic circuits?
In series circuits,all electrical switches will have common switch.So they cannot be turned off/On separately.
The voltage will be divided across all electrical appliances .Damage of one component disconnects the whole circuit.
Q)How does the resistance of a wire vary with its area of cross-section?
The resistance is inversely proportional to the area of cross section of the wire. That is,the more is the area of cross section of the wire,the less is the resistance and the less the area,the more is the resistance.
✦R ∝ 1/Area of cross section
Q)Why are copper and aluminium wires usually employed for electricity transmission?
Copper and aluminium are good conductors of electricity.They have very low resistance.Hence they decrease the rate of resistance and allow the current to flow through them easily and the current is not wasted in large amount.Hence, they are used to make wires for electrical transmissions.