# Electric field of Charge in above picture,we have a fixed positive charge. this positive charge create electric field in its surrounding.

we consider a special point in left of positive charge.

Is electric field different at that point when we put negative or another positive charge there?

state 1 refer to absence another charge and state 2 refer to presence a negative charge at that point.

• I think electric field increases and direction of filed is to left.correct? – user3728644 Jul 30 '19 at 9:44
• because of this we must use infinitesimal test charge to measure electric field of another charge. because this test charge has no effect on electric field of main charge. correct? – user3728644 Jul 30 '19 at 9:47
• Related question Electric field at location of a charge due to the charge itself? – Aaron Stevens Jul 30 '19 at 11:47

If on the other hand you have an extended spherical charged sphere placed at the point you are measuring the E-field, the answer depends. If the free charge distribution in this sphere is spherically symmetric and the sphere is a non-polarizable insulator (its permittivity is $$\epsilon_0$$), then the value of the E-field is not affected by this sphere. This is because the E-field here is the superposition of the E-field due to the charged sphere and the positive charge on the right, and because of the spherical symmetry, the E-field due to the sphere at the center of this sphere is zero.
In other cases, if you still assume extended charges, but the charge distribution is no longer spherically symmetric or the charged object is made of a dielectric with $$\epsilon \ne \epsilon_0$$, the E-field will in general be different from the case with only the positive charge.