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### Course: AP®︎/College Physics 2>Unit 2

Lesson 2: Electric fields

# Magnitude of electric field created by a charge

An electric field is a vector field that describes the force that would be exerted on a charged particle at any given point in space. A point charge is concentrated at a single point in space. Learn about the formula used to find the magnitude and direction of the electric field between two point charges, and see two examples of how to calculate the magnitude of an electric field. Created by David SantoPietro.

## Want to join the conversation?

• Should not the direction depend upon the type of charge that is whether the charge is positive or negative not only for the central charge but the test charge too. Like I have a negative charge and I bring a positive test charge, will the same maths apply?
• The electric field stays the same whether your charge is positive or negative. What changes is the direction of the electric force generated by that field.
• Why aren't the electric field lines closed as that of magnetic?
• E fields can be closed loops if they are formed from a changing magnetic field.
But E fields from a charge source will not be closed loops. B fields however will always be closed loops. This comes out of Maxwell's equations.
• So, does the formula mean that you could infinitely far from a charge but the electric field will still be acting?
Thanks!
• Yes! , definitely , you are being atracted gravitationally by starts thousands of light years from you , but very very slightly
• how can coulomb's law be used to describe the electric force between a neutral object and a charged object? although neutral object is polarized, the overall charge of it is 0 so the product of k*Q1*Q2 is 0. Also, how did Coulomb get the constant k? Does a polarized neutral object have electric field?
• Maybe it would be more clear if the magnitude of the electric field was said to be equal to k times the absolute value of the charge creating the field divided by the distance squared. This would eliminate the discussion about whether or not to include the sign in the computation.
• Isn't Q2 zero and so is force at that point?
• If there's only one charge, there's no force, but there's still a field from that charge. Don't confuse E with F.
• Do field lines of an electric field only depict its direction ?
• the distance between them (or their density) indicates the strength
• What is the difference between electric field and magnitude of electric field?
• Electric field is basically a vector quantity.
It has a direction. So, either it will be a positive vector or negative one.
So, coming to your point, Electric field as I told can be negative or positive but when we consider magnitude of we only consider the number not the sign.
Hope you got the answer :)
(1 vote)
• Are all protons are identical ?
• It depends on what you mean by identical. The intrinsic attributes of the proton like spin, charge and a few others are the same but the attributes like position and momentum are not the same.

There is a subtle aspect of protons and neutrons that you could argue that there are 3 types of protons and 3 types of neutrons. Protons and neutrons are composite particles, they are not fundamental particles. They are made of quarks, a proton is 2 up quarks and 1 down quark where as the neutron is 1 up and 2 down quarks. Quarks have a different type of charge related to the strong nuclear force/interaction that is called color charge. Color charge has 3 values: Red, Green, Blue. These color charges have nothing to do with colors we see in the world around us. The proton has no net color charge so it has to have a quark of each of the colors. With 1 down quark and 2 up quarks the possible combinations are:
Type 1: Red Down quark and a Green and Blue Up quarks
Type 2: Green Down quark and a Red and Blue Up quarks
Type 3: Blue Down quark and a Red and Green Up quarks

Even with these 3 type of proton the strong nuclear force causes the quarks to change color charge so a single proton is continually changing between the 3 types so you can't say that a specific quark is a specific type so while there are 3 types of protons they are effectively the same.