Over time, atoms \"boil off\" the hot filament in an incandescent bulb and the f

Question

Over time, atoms "boil off" the hot filament in an incandescent bulb and the filament becomes thinner.

Part A

How does this affect the brightness of the lightbulb?

the brightness does not change

Multiple Choice Question 22.27

Part A

If a 1.8 battery stores 6.8 of energy (a reasonable value for an inexpensive C cell), for how many minutes could it sustain a current of 1.2 ?

the brightness increases the brightness decreases

the brightness does not change

Multiple Choice Question 22.27

Part A

If a 1.8 battery stores 6.8 of energy (a reasonable value for an inexpensive C cell), for how many minutes could it sustain a current of 1.2 ?

2.9 min 6.8 min 9.5 min 52 min

Explanation / Answer

1)the brightness decreases

Because the resistance increases, as R varies, R = rho L/A; less the cross sectional area, more the resistance. Power dissipated would be less and hence its brightness decreases.

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Ans: 52 min

explanation

we know that, Power is:

P = VI = 1.8 x 1.2 = 2.16 W

Also, P = E/t

t = E/P = 6.8 x 10^3/2.16 = 3148 s

t = 3148s = 3148/60 = 52 min

Hence, t =52 min

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