problem in electrostatics

[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....

[Doc Al]

Use Coulomb's law.

[nisha]

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

[cookiemonster]

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?"

cookiemonster