00:01
All right, so let's say the electric field at earth near the surface is 167 newtons per kulam directed downwards.
00:11
And so for part a, we want to know what's the surface charge density of the ground.
00:16
So basically, we're going to treat the electric field as coming from an infinite plate.
00:20
So this will be sigma over epsilon not, or sigma over two epsilon not.
00:27
And so we can see sigma is two epsilon not times our electric.
00:31
Field strength.
00:33
And so this will be negative 2 .96 times 10 to the negative 12th kulams per square meter.
00:42
And then part b asks, if the surface charge density is uniform over the whole planet, then what's the charge of earth? so this is going to be the surface area of earth times the surface charge density.
00:54
All right.
00:55
So this is about negative 1 ,5007 .2 coulams.
01:00
Part c, and part c, asked what is the electric potential due to this charge so v is just going to be k times q over the radius of earth and so if we do that this is about 2 .13 time and negative 2 .13 times 10 to the 6th volts and then part d what's the difference in potential between the head and feet of a person in 1 .5 meters tall so basically delta v is going to be negative e times you know, delta y, i guess.
01:36
And so this is 252 .17 volts...