having lots of trouble with a few problems that are due tonight...please help!!!

[supermenscher]

1. A 0.28F capacitor is desired. What area must the plates have if they are to be separated by 1.2mm air gap?

I used C=E0 (A/d) and I keep getting the same and wrong answer. What am I doing wrong?

2. What potential difference acting over a distance of 3.5cm would be needed to balance the downward force of gravity so that an electron would remain stationary? Assume the electric field is uniform.

I used V=mass of electron*gravity*0.035m/1.6*E-19, and that gave me the wrong answer. Help anyone.

3. A 9.4V battery is connected to a bulb whose resistance is 2.1ohms. How many electrons leave the battery per minute.

I used ohm's law I=9.4/2.1 to get the current 4.476C/s. Then I multiplied 4.476c/s*60s/1.6E-19 and got 1.68E-17 electrons/minute...and that answer was wrong...any help?

[Doc Al]

Your methods all look correct. Show your work in the first two problems--I suspect an arithmetic error. That's what happened in problem 3: check those exponents.

[supermenscher]

I still keep getting the wrong answers can you show me what to do...I just plugged the numbers into the formulas

[Doc Al]

You know what to do, you are just making arithmetic errors. Show the actual numbers you are plugging into the equations.

For example, you showed your work for problem 3: The numbers are right, but the answer is wrong. Redo your calculation carefully. You messed up the exponent in the answer.