Question

19. a) Though same current flows through the electric line wires and the filament of bulb,
yet only the filament glows. Why?
(b)The temperature of the filament of bulb is 2700°C when it glows. Why does it not get
burnt up at such high temperature?
(c)The filament of an electric lamp which draws a current of 0.25 A is used for four hours.
Calculate the amount of charge flowing through the circuit.

(d) An electric iron is rated 2 kW at 220 V. Calculate the capacity of the fuse that should be
used for the electric iron.
(e). copper wires are used in transmission lines.

Answer 1

Explanation:

a) The cord of electric line wires is made up of thick copper wires which means it has low resistance and if there is low resistance the current will easily pass through it without any heating and hence will not glow.

But the filament of bulb has very high resistance which in turn will produce very large amount heat(acc. to Joule's law of heating-H is directly proportional to R) so more heat will produce a glowing effect on filament and thus gives us light.

b) The filament of Bulb is made up of Tungsten which has a very high melting point i.e. 3422°C.So it will not burn up till it attain 3422°C.

c)I=Q/t

0.25=Q/14400sec

Q=14400*0.25

Q=3600Coulombs.

d) P=VI

2000=220*I

I=2000/220

I=9.02 A

e) This answer is Mentioned above.(a)