Question

Please check my answers: 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)

Answer 1

1) 30 volts is correct
2) Rt = (4x6)/(4+6)=2.4 Ω
3) P = I^2 x R = 36 W

we use AC because it's easy to transmit via 3 phase on cables and easy to step up and down