A resistor uses 100 w of power when connected to 120 v emf. What is the current through the same resistor when connected to a 220 v emf?

Let the resistance of resistor be R.

Power of resistor V² / R, where V is potential applied.

V² / R = 100

120² / R = 100

R = 120² / 100

= 144 ohm.

Now potential diff applied = 220 V

current = potential diff / resistance

= 220 / 144

= 1.53 A approx.