# Electric Charge of Earth

https://isaacphysics.org/questions/rmets_electric_charge_of_earth?board=d5cd3e50-abfc-42f3-9182-00b6845709ae&stage=a_level

Stuck on Part B, how can the Gauss's Law be applied to solve the problem, it is extremely confusing that there's no electric field inside the earth and so it can't be treated as a point charge.
Original post by Fach1mo
https://isaacphysics.org/questions/rmets_electric_charge_of_earth?board=d5cd3e50-abfc-42f3-9182-00b6845709ae&stage=a_level

Stuck on Part B, how can the Gauss's Law be applied to solve the problem, it is extremely confusing that there's no electric field inside the earth and so it can't be treated as a point charge.

How do you apply Gauss’s law for part A?
Do the same but this time the “radius of the sphere” is the radius of the Earth plus 100 m.
all you do is just do the same in part b and divide by change in V
Original post by Eimmanuel
How do you apply Gauss’s law for part A?
Do the same but this time the “radius of the sphere” is the radius of the Earth plus 100 m.
I did 100*4pi*(6371100)^2, it seems incorrect
Original post by mosaurlodon
all you do is just do the same in part b and divide by change in V
I did 100*4pi*(6371100)^2 and divided by 50, which seems incorrect
You have to use volume equation 4/3 pi r^3 NOT surface area
The equation you should have is (q_a - q_b)/(V_a-V_b)
q_a you calculated.
q_b can be calculated using the same equation.
V_a and V_b can be calculated using the above equation in previous post.