Light bulb resistance question!

Question

Hello Everyone,

I'm new at this yahoo answers thing. So I hope you can help me figure out some questions I have on my work.

Thanks to all who help me!!

A 95 watt light bulb uses 95 watts of power (i.e., time averaged power) when its lamp is plugged into a wall socket (alternating emf at a frequency of 60 hertz with RMS voltage 120 volts). Determine the electrical resistance of the light bulb filament.

Answer 1

The others have correctly calculated the resistance of the filament while it is hot. However, you will get a much lower reading if you measure it with an ohmmeter because tungsten wire has 17.62 times more resistivity at 3200 deg K than it does at 300 deg K; the cross sectional area expands only about 0.3 percent, and the length expands by about .155 percent. That makes the resistance of the fillament about 17.6 times greater at 3200 deg K than it is at 300 deg K.

The fillament also has a very slight electrical impedence due to its helical shape. You might need to know how much impedence it has at 60Hz if you want a highly accurate result.

My answer was delayed about 8 hours because of symbols for deg and percent. This is a bug in the new format.  

Answer 2

Simplicity itself, when you know the equation!

Using Ohm's law, R = V^2 / P.  So, R = (120V)^2 / 95W.  This gives you a resistance of 151.5 Ohms.

I hope this was helpful.

Answer 3

P=95w,F=60Hz,V=120v,R=?

P=v^2/R  95=120^2/R 14400/95=R   151.57ohms

Answer 4

P = E²/R

95 = 120²/R

R = 120²/95 = 152 ohms

.