1. An AC power generator produces 25 A (rms) at 3 600 V. The energy is transmitt
ID: 2299199 • Letter: 1
Question
1. An AC power generator produces 25 A (rms) at 3 600 V. The energy is transmitted through a long-distance power line, which has a total resistance of 100 ohms. What percentage of the power delivered by the generator is dissipated as heat in the long-distance line if a step-up transformer is not used? a.
0.09%
b.
1.8%
c.
32%
d.
69%
2. An electromagnetic wave with a peak magnetic field component of 1.5x10^-7 T carries what average power per unit area? (u0 = 4pi x10^-7 Txm/A, E0 = 8.85x10^-12 C2/Nxm2 and c = 3.0x10^8 m/s) a.
12 W/m2
b.
2.7 W/m2
c.
3.0 W/m2
d.
1.3 W/m2
Determine the amount of energy carried in l.0 m of a 3.5-mW He-Ne laser beam if the cross-sectional area of the beam is 5.0 x10^-6 m2. a.
0.012 J
b.
4.1x 10^
1. An AC power generator produces 25 A (rms) at 3 600 V. The energy is transmitted through a long-distance power line, which has a total resistance of 100 ohms. What percentage of the power delivered by the generator is dissipated as heat in the long-distance line if a step-up transformer is not used? a.
0.09%
b.
1.8%
c.
32%
d.
69%
Explanation / Answer
1) Is = Ip Vp / Vs = 25 * 3600 / 100000
= 0.9
Pavg = V I = 0.9 * 100000 = 90000 W
Energy dissipiated = I2 R = 0.92 * 100 = 81 W
percentage = 81 / 90000 * 100
= 0.09 %
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2)Eo = C Bo / 2 mu
= 3 * 108 * (1.5 * 10-7 )2 / 2 4 pi * 10-7
= 2.7 W/m2
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3) U = p I / c
= 3.5 * 10-3 * 1 / 3 * 108
= 1.2 * 10-11 J
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4) v = c/lambda
= (3.00*108) / (10*10-10)
= 3.00 * 1018 Hz
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5) All of the above give the same shift.
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6) red shift
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