What current flows through the bulb of a 3.15 V flashlight when its hot resistan

Question

What current flows through the bulb of a 3.15 V flashlight when its hot resistance is 3.85 a? If the 0.150 mm diameter tungsten filament in a light bulb is to have a resistance of 0.200 at 20.0 degree C, how long should it be? What current flows through a 2.58 cm diameter rod of pure silicon that is 18.0 cm long, when 1000 V is applied to it? (Such a rod may be used to make nuclear particle detectors, for example.) A certain circuit breaker trips when the rms current is 10.5 A. What is the corresponding peak current? A tourist takes his 22.5 W, 120 V AC razor to Europe, finds a special adapter, and plugs it into 230 V AC. Assuming constant resistance, what power does the razor consume as it is ruined?

Explanation / Answer

(1)

I = V/R =3.15/3.85 = 0.8181 A

(2)

R = rho L/A

L = RA/ rho.

=0.2(pi ( 0.150* 10^-3 /2)^2/5.6* 10^-8

=6.3 * 10^-2 m

(3)

I = V/R = V/  rho L/A

=1000 V/(0.1)(0.18)/ pi (2.58 * 10^-2/2)^2

=29 A

here rho I took 0.1 it varies from 0.1 to 60 if you have particular value you will get different answer

(4)

I _rms = I_max/ sqrt 2

I_max = 10.5 ( 1.414) = 14.847 A

(5)

P1= V1^2/R

P2 = V2^2/R

P2= P1 (V2/V1)^2.=22.5( 230/120)^2 = 82.65625 W

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