A stereo system draws 2.4 A at 120 V. The audio output power is 50 W.?

S

Shahad

New member
A stereo system draws 2.4 A at 120 V. The audio output power is 50 W.
a- How much power is lost in the form of heat in the system?
b- What is the efficiency of the system?
 
R

reelslick

New member
P = I*V
P = 2.4A * 120V
P = 288 W

if the output power is 50W, the efficiency of the output is
50W/288W ~ 17%

how much power is lost to heat is not obvious. there are other sources of losses besides heat (the efficiency of the speakers themselves etc etc).
but i guess we're supposed to assume that all inefficiency goes into heat. if so, 288W-50W = 238W is lost to heat (?).

cheers
 
N

npolynomial

New member
If the 120V input is peak voltage of an alternating current... and if the waveform is a sine wave you'll have to multiply by the average value of a sine wave which is the squareroot of 2 divided by 2... approximately 0.707 * peak...

That means that the average voltage is 84.84 volts, multiplying that by 2.4amps = 203.616 watts

153.616 watts of power are lost due to inefficiencies.

-NPolynomial
http://novaconceptions.blogspot.com
 
K

KENNETHW

New member
If the stereo system is 50 watts per channel; and using ohms law, the output would equal around .8 amps: which means that 1.6 amps of power is unaccounted for...due to heat, or resistance, or a small amount of voltage drop. Not sure about the effiecency...but it would not seem to be all that great.
 
W

wjllope

New member
P = I*V
P = 2.4A * 120V
P = 288 W

if the output power is 50W, the efficiency of the output is
50W/288W ~ 17%

how much power is lost to heat is not obvious. there are other sources of losses besides heat (the efficiency of the speakers themselves etc etc).
but i guess we're supposed to assume that all inefficiency goes into heat. if so, 288W-50W = 238W is lost to heat (?).

cheers
 
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