In a dentist's office, an X-ray of a tooth is taken using X-rays that have a frequency of 9.81 1018 Hz. What is the wavelength in vacuum of these X-rays?

Explanation:

The equation that involves frequency (f) and wavelength () of a wave is , where v is the speed of the wave. X-rays are a type of electromagnetic wave, so in vacuum it moves at the speed of light c, which means that our wavelength will be:

r=rho l/a where a is the area, l is the length and rho is resistivity so the greater the area the lesser the resistance thats why the earth pin is thicker bcos current follow the shortest path, so less resistive .