PLEASE SHOW ALL WORK. THANKS. 1. [2pt] A #14 copper wire has a diameter of 1.628
ID: 1451441 • Letter: P
Question
PLEASE SHOW ALL WORK. THANKS.
1. [2pt]
A #14 copper wire has a diameter of 1.628 mm. Calculate the resistance of a 31 m long piece of such wire. Use = 1.72x10-8 m for the resistivity of copper.
Answer:
2. [2pt]
A typical household circuit is capable of carrying 30.0 A of current at 120 V before the circuit breaker will trip. How many 1500 W hair dryers can run off one such circuit?
Answer:
3. [2pt]
In the rush to get ready for lecture, a physics professor leaves the hair dryer described in the previous problem running and does not turn it off until he gets home 6.7 hours later. If electricity costs $0.078 per kilowatt-hr, how much will this add, in dollars, to his next electric bill? [Please enter the answer with no units]
Answer:
4. [2pt]
When a defribillator is used, 17.0 A of current passes through the patients body for 0.06 s. How much charge goes through the patient's skin?
Answer:
5. [2pt]
A current of 4.0 A is maintained in a circuit with a total resistance of 1.5 . How much heat is generated in 2.0 s?
Explanation / Answer
1) R = rho*L/A
= 1.72*10^-8*31/(pi*0.001628^2/4)
= 0.256 ohms
2) no of hair dryers, N = P_output/P_hairdryer
= 30*120/1500
= 2.4
3) energy consumed in 6.7 hours, E = power*itime
= 30*120*6.7*60*60
= 86832000 J
= 86832000/(3.6*10^6)
= 24.12 KWh
so, total cost = 24.12*0.078
= $1.88
4) Q = i*t
= 17*0.06
= 1.02 C
5) Heat generated = P*t
= (I^2R)*t
= 4^2*1.5*2
= 48 J
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