CURRENT ELECTRICITY

1. 
   where P is the power dissipated when a current I is driven by a potential difference V.
2. The definition of resistance:
   
   where R is the resistance of a material when a potential difference V across it drives a current I.
3. Ohm’s Law:
   A conductor obeys Ohm’s law if the potential difference, V, across its ends is directly proportional to the current, I, flowing through it whenever the temperature is constant, i.e.
   
4. 
   where R is the effective resistance of three resistors in series.
5. 
   where R is the effective resistance of three resistors in parallel.
6. 
   where  is the resistivity of a conductor of uniform cross section A, length l and resistance R.
7. 
   where  is the resistivity of a wire of diameter d, length l and resistance R.
8. Wheatstone Bridge Formula (when the bridge is balanced):
   

9. Joule’s Law:
   
   the heat, W, liberated when a current I flows through a wire of resistance R for a time t.
10. 
    where P is the power developed in a wire of resistance R when it carries a current I.