Explain the following: (i) Why is tungsten used almost exclusively for filament of electric lamps ? (ii) Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal ? (in) Why is the series arrangement not used for domestic circuits ? (iv) How does the resistance of a wire vary with its area of cross-section ? (v) Why are copper and aluminium wires usually employed for electricity transmission?
Answers
Answer:
Electrical resistance is directly proportional to the length (L) of the conductor and inversely proportional to the cross-sectional area (A). ... Resistance is inversely proportional to the area of cross-section. When the area of cross-section increases the resistance decreases and vice versa.
Explanation:
(I)The metal tungsten is almost exclusively used for the filament of the electric lamp because it has a very high melting point due to which it does not melt even when it is heated to high temperatures due to the passage of electric current.
(ii)
The conductors of electric heating devices such as bread toasters and electric irons are made of alloy because the resistivity of an alloy is more than that of metals which produces a large amount of heat. At high temperatures, the alloys do not oxidize. Alloy does not melt readily and get deformed.
(iii)
Each component of a series circuit receives a small voltage so the amount of current decreases and the device becomes hot and does not work properly. ... Hence, the series arrangement is not used in domestic circuits.
(iv)
Electrical resistance is directly proportional to the length (L) of the conductor and inversely proportional to the cross-sectional area (A). ... Resistance is inversely proportional to the area of cross-section. When the area of cross-section increases the resistance decreases and vice versa.
(v)
copper and aluminium wires usually employed for electricity transmission because they are good conductors of electricity
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Answer:
1) The metal tungsten is almost exclusively used for the filament of the electric lamp because it has a very high melting point due to which it does not melt even when it is heated to high temperatures due to the passage of electric current.
2) The electrical heating devices such as toaster or electric iron is made of an alloy rather than pure metal because if electrical heating devices are made by pure metal then the metal melts easily when heat is increased and pure metal gets corroded easily.
3) In series circuits voltage is divided. Each component of a series circuit receives a small voltage so the amount of current decreases and the device becomes hot and does not work properly. Hence, the series arrangement is not used in domestic circuits.
4) Copper and aluminium are good conductors of electricity also they have low resistivity. So they are usually used for electricity transmission. They have very low resistance and allow the current to flow through them easily. Hence, they are used to make wires for electrical transmissions.