# Electrical power

• Oct 17th 2009, 02:42 PM
Raul780
Electrical power
Which requires the most electrical power during operation?

1. A 12 volt motor requiring 8 amperes.
2. Four 30 watt lamps in a 12 volt parallel circuit.
3. Two lights requiring 3 amperes each in a 24 volt parallel system.
• Oct 17th 2009, 02:43 PM
e^(i*pi)
Quote:

Originally Posted by Raul780
Which requires the most electrical power during operation?

1. A 12 volt motor requiring 8 amperes.
2. Four 30 watt lamps in a 12 volt parallel circuit.
3. Two lights requiring 3 amperes each in a 24 volt parallel system.

Power = Potential Difference x Current

$\displaystyle P = VI = I^2R = \frac{V^2}{R}$
• Oct 21st 2009, 07:56 AM
PT321
Hello Raul: see if this helps:

for case 1, power P =V(volts)* I(amperes), P = 12*8=96W

for case 2, you have to determine whether you can use any of the three Ohms Law formulas for power: P=VI, P=V^2/R, P=I^2*R. Because you are only given one measurement, the voltage V, and I is not defined, and R is not defined, you cannot find the total power with Ohms Law. The answer is allready given in implied form:

total Watts = P = (30W + 30W + 30W + 30W) =120W

for case 3 you have two measurements and so can use
P = VI for each bulb: P=24*3=72W per bulb, since you have two bulbs the total P = 2(24*3)= 144W.

The most power is used in case 3.
• Oct 22nd 2009, 06:49 AM
CaptainBlack
Quote:

Originally Posted by Raul780
Which requires the most electrical power during operation?

1. A 12 volt motor requiring 8 amperes.
2. Four 30 watt lamps in a 12 volt parallel circuit.
3. Two lights requiring 3 amperes each in a 24 volt parallel system.

1. 8 amps through 12 volts

2. 4 x 30 watt lamps = 120 watts

3. 3 x 2 amps=6 amps through 24 volts (the lamps are in parallel so each is drawing 3 amps)

CB