# Problem in electrostatics

1. Mar 13, 2004

### nisha

we meet again .. here ,i have a question about electrostaatics...
in a particular experiment, a high voltage is created by charging an isolated metal sphere,the sphere has diameter 42 cm and any charge on its surface may be considered as if it were concentrated at its centre. The air surrounding the sphere loses its insulating properties, causing a spark, when the electric field exceeds 20kvcm-1... Calculate the charge on the sphere and its potential,
i know this question involving the equation v=Q/4pi(permittivity of free space)r but how to calculate the charge if we are given electric field?need help....

2. Mar 14, 2004

### Staff: Mentor

Use Coulomb's law.

3. Mar 27, 2004

### nisha

hello.. tell me more about quantum physics and photoelectric effect.. Is x-ray one of application of photoelectric effects...

4. Mar 28, 2004

Why don't you try doing a bit of research about it on your own first? If you have a specific question, we'd be more than happy to answer that, but explaining the entire thing from scratch would be like reinventing the wheel.

And x-rays are just electromagnetic waves with a wavelength in a specific range. What do you mean by "application?"