It's not that hard. Let me explain...
There are two ways to remember this.
The first one is by using the formula for the electric strength (E)
E = k × (Q / r^2) , where:
- k is a constant
- Q is the "central" charge. The one producing the electric field. Not the one we use to test it.
- r is the distance between the charges
As you can see, field's strength is proportional to the magnitude of Q, and inverse proportional to the square of the distance. The field does not care how much you alter the charge you positioned in ot to test it.
Although that is the only way to work out the problem, there are many ways to remember it. Given that i have difficulty in remembering formulas, i always try to derive it from something i know.
By definition: E is equal to the force acted on the test charge, divided by its value.
E = F / q
- F --> Coulomb's force
- q --> test charge
Since i remember that:
F = k ( Q × q) / r^2
just take out from the expression the q term, since you divided by it, and all it remains is the strength of the field.
In other words, the strength changes as long as something from the expression is altered.
