I have three questions -- help please!! :( 1.) Calculate the diameter of a 3.19

Question

I have three questions -- help please!! :(

1.) Calculate the diameter of a 3.19 cm long tungsten filament in a lightbulb if its resistance is 0.449 . (The resistivity of tungsten is 5.60×10-8 m.)

2.) If a copper wire has a resistance of 31.2 at a temperature of 19.2 oC, what resistance does it have at 95.0 oC? (Neglect any change in length or cross-sectional area resulting from the change in temperature.)

3.) How much does it cost in dollars to watch the 5.20 hour-long coverage of the Super Bowl on a 145 Watt television set? Assume that one kWh electricity costs 9.25 cents.

Explanation / Answer

The electrical resistance of a wire is given by
R = (p * L)/A
where,
R = Resistance of wire = 0.448 ohm
p = Ressistivity of wire = 5.6 * 10^-8 ohm-meter
L = length of wire = 3.19 * 10^-2 m
A = area of cross section = 3.14 * (d/2)^2
where d = diameter of wire.

Substituting Values -
R = (p * L)/A
A = (p * L) / R
3.14 * (d/2)^2 = (5.6 * 10^-8 * 3.19 * 10^-2) / 0.449
d/2 = sqrt((3.98 * 10^-9) / 3.14)
d = 2 * sqrt((3.98 * 10^-9) / 3.14) m
d =  7.127 * 10^-5 m
Diameter of wire d = 7.127 * 10^-5 mm

Please post seperate question in seperate post

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