a 4 ohm resistor is connected across a 12 volt battery.How much power will the resistor dissipate?

 

Hello,

Take a look at this page of the AAC eBook.
http://www.allaboutcircuits.com/vol_1/chpt_2/4.html

Greetings,
Bertus

 

P=V*I or

P=(V^2)/R or

P=(I^2)*R

where

P=power in Watts
V=voltage across the resistor in Volts
I=current through the resistor in Amps
R=resistance of the resistor in Ohms

Choose one and make the calculation, the second one suits better in your case because you know the voltage across the resistor and R.