Question

explain how you can determine how much power a circuit will generate if you know the voltage and resistance but not the current

Answer 1

The general formula for power dissipation is:
Power = Current x Voltage
However, if you only know the voltage and the resistance, you can calculate the current using Ohm's Law, which is usually given as:
Voltage = Current x Resistance
However, you can rearrange this to give:
Current = Voltage/Resistance
You can then substitute this into the expression for power dissipation to yield an equation that gives an expression for power in terms of only voltage and resistance:
Power = $Voltage^{2}$ / Resistance