Question 7

7.1 Two small, identical spheres, P and T, are placed a distance of 0,1 m apart, B as shown in the diagram below. P carries a charge of +3 x 10^-6 C and T carries a charge of -3 x 10^-6 C.

7.1.1 State Coulomb’s law in words. (2)

7.1.2 Draw the resultant electric field pattern due to the charges on P and T. (3)

A third charged sphere S of unknown charge Q_s is placed a distance of 0,15 m from sphere T such that the three charged spheres are at the vertices of a right-angled triangle.
The net electrostatic force on sphere T due to the other two charged spheres has a magnitude of 10 N, as shown in the diagram below.

7.1.3 Is charge Q_s POSITIVE or NEGATIVE? (1)

7.1.4 Calculate the number of electrons added to or removed from sphere S to give it a charge of Q_s. (6)

7.2 P is a variable point in the electric field of charged sphere A and r is the distance between point P and the centre of sphere A. See the diagram below.

A learner determines the magnitude of the electric field (E) at point P for different values of r.
Sphere A is then replaced by another sphere, B, of a different charge. Another set of results are obtained.
The graphs below are obtained from the results for sphere A and sphere B.
E_A is the magnitude of the electric field at a distance of 0,04 m from the centre of charged sphere A.