Help with electric field, potential, and resistance homework

[thspoq2]

Im doing some homework problems and I cannot figure out how to do these for the life of me. Any help would be appreciated.

1. An airplane is flying through a thundercould at a height of 2000 m. If there is a charge concentration of +40 C at 3000 , within the cloud and -40 C at height 1000 m, what is the electric field at the aircraft?

2. Two point charges of values +3.4 and +6.6 C are separated by .10 m. What is the electrical potential at the point midway between the two point charges?

3. If a lamp has resistance of 120 Ohms when it operates at 100W, what is the applied voltage?

4. The temperature coefficient of resistivity for a "perfect" ohmic material would be?

 

[thspoq2]

Sorry, make it 5.

5. A pair of parallel plates, forming a capacitor, are charged. The plates are pulled apart to double the original separation, the charges on the plates remaining the same. What is the ratio of the final energy stored to the original energy stored?