Electricity?

Question

can u guys help me please.

How much would you have to raise the temperature of a copper wire (originally at 20C) to increase its resistance by 20 percent?

A length of aluminum wire is connected to a precision 10.00 V power supply and a current of 0.4212 A is precisely measured at 20C. The wire is placed in a new environment of unknown temperature where the measured current is 0.3618 A. What is the unknown temperature?


What is the maximum power consumption of a 9.0 V portable cassette player that draws a maximum current of 350 mA of current?

Answer 1

The temperature coefficient of resistance for copper is 0.0039 1/ºC. The resistance is

R(T) = R(20ºC) *[1 + ∆T*0.0039]

An increase of 20% from 20ºC is R(20ºC)*(1+0.2), so
∆T*0.0039 = 0.2, ∆T = 51.28ºC

The initial resistance of the aluminum wire is 10.00/0.4212 = 23.74 ohms, and this is at 20ºC In the new environment, R = 10.00/0.3618 = 27.64 ohms. ∆R = 3.9 ohms.

From the above equation, R(T)= R(20ºC)*(1+∆T*K). For aluminum, K = 0.0039, so

R(T) = R(20ºC)*(1+∆T*0.0039)

27.64 = 23.74*(1+∆T*0.0039)

1.164 = 1 + ∆T*0.0039

0.164 = 0.0039*∆T

∆T = 42.12ºC

The new temp is this plus 20ºC, or 62.12ºC

Power = Voltage * Current, 9.0*0.350 = 3.15W