# Physics

The voltage across a 10-ohm resistor carrying 3 amps must be? I got 30 volts-v=?, I=3 amps, R= 16 ohm. v= 30 amps * 10 ohm=30 volts

A 4-ohm resistor is connected in parallel with a 6 ohm resistor. What is the total resistance of this pair of resistors? I got 6.87 ohms
rt=r1+r2/r1+r2 = rt= 4 ohm+6ohm/4 ohm+6ohm= rt=.25+.167/.25+.167=6.87
how I got .25 and .167 its from the decimal 1/4=.25 and 1/6=.167

The power dissipated in a 4-ohm resistor carrying 3 amps is? I wasn't too sure about this one, but I got 12 watts this is how I did it: power=current * voltage, power= 4 ohm* 3 amps= 12 watts

What is a device that produces AC electricity? Why does our power grid use AC electricity? (For the first part I got an alternator and for the second part I don't understand)

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1. 1. 30 volts is correct
2. 6.87 is not correct
For parallel resistors,
1/RT = 1/R1 + 1/R2 + 1/R3...
For two resistors, 4 ohm and 6 ohm
1/RT = 1/4 + 1/6

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2. 3. 12 watts is not correct
A 4 ohm resistor carrying 3 amps has a voltage drop of 3 * 4 or 12 volts.
The current throught the resistor is 3 amps. Volts * Amps = 3 * 12 = 36 Watts.

4. AC voltage is easily changed with a transformer. High voltage is good for long distance transmission since for the same power, the current is less at higher voltages. For a fixed resistance of a transmission line, high voltage/low current has lower heating losses. For consumer use, the higher voltage is converted back to the lower voltage required by most user products.

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3. Name a device that produces DC electricity. What does 60Hz, 120V electricity mean?

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