A length of metal wire has a radius of 0:002 m and a resistance of 0.1. When the potential difference across the wire is 14 V, the electron drift speed is found to be 0:000229 m/s. Based on these data, calculate the density of free electron in the wire. Answer in units of m^-3.(adsbygoogle = window.adsbygoogle || []).push({});

r=.002m R=.1 Vd=.000229

V/R=i

14/.1=140

Vd= drift velocity.

i/(Vd*A)=ne

140/(.000229*pi*.002squared)=4.86499826e10

j=neVd

11140846.02 (I tried plugging in this answer, it's wrong)

11140846.02/1e-3 = 1114084602e10 (I did this because it says answer is

supposed to be in 1e-3)

The answer is wrong I don't know why.

A 72:5 W, 191.2 V light bulb is plugged into a 61:6 V outlet. If energy costs 4.7 cents/kWh, how much does it cost per month (30 days) to leave the light bulb turned on? Answer in units of

cents.

light bulb = 72.5W, 191.2V

outlet = 61.6V

Energy = 4.7 cents/kWh

Days = 30

P/V = i

72.5/191.2 = .3791841

i*V=P

.3791841*61.6 = 23.35574059W

23.35574059/1000 = .02335574059kW

Pt = P*t

.02335574059*30*24 = 16.81757322

Cost = P*cents

16.81757322* 4.7 = 79.04259414 cents

This is also wrong, I don't know why.

Any help is appreciated.

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# Homework Help: 2 problems

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