Physics practice test can someone help? A 120V (rms) power source is to be conne
ID: 1384829 • Letter: P
Question
Physics practice test can someone help? A 120V (rms) power source is to be connected to a remote cabin by a pair of long wires with a total resistance of 0.3 ohms (a very long extension cord). 12KW of power is being drawn from the power source, (a) In situation I) shown below, what is the rms current in the cables? (b) What is the average power dissipated in the cable in situation I ? (c) What is the mis line voltage at the cabin in situation I ? (d) Now if a pair of ideal transformers w ith turns ratios of 100:1 are used as shown in II) below, what is the rms current in the cable? (c) Mow- much power (average) is dissipated in the cable for situation II? (f) What is the rms line voltage at the cabin in situation II?Explanation / Answer
Given that,
rms voltage of the cables is Vrms=120 V
total resistance R= 0.3 ohms
the power is dissipated by P=12 KW
a)
P=Irms2R =>Irms=sqrt(P/R)
substitute the values in above,
Irms=20 A
b)
Paverage=Vrms^2 /R
= 1202 V/0.3 ohm
=48 KW
c)
at cabin line voltage is,
V=I*R
=20 A*0.3 ohm
= 6 V
d)
in transformers no of turns ratio is N1:N2=100:1
the secondary current is passing through near the cabin is,
I2/I1=N1/N2
I2/20=100/1
I2=2*10^3 A
e)
the average power dissipated through the cables is,
Paverage=Vrms^2/R
=1.22 V / 0.3 ohm
= 4.8 W
f)
rms line voltage at cabin,
V1/V2=N1/N2
120/V2=100/1
V2=1.2 V