In a diagram of charges and electric field lines charge has twelve field lines going outward from it and charge has three field lines going into it. If one of the charges is 100 nC, what is the other one?
A) 25 nC
B) 100 nC
C) -25 nC
D) -100 nC
E) Both answers b and c can be correct.

Question

In a diagram of charges and electric field lines charge  has twelve field lines going outward from it and charge  has three field lines going into it. If one of the charges is 100 nC, what is the other one?
A) 25 nC 
B) 100 nC 
C) -25 nC 
D) -100 nC 
E) Both answers b and c can be correct.

Quizplus · Accepted Answer

The number of field lines going out from or into a charge is directly proportional to the charge. Since one charge has 12 field lines going outward while the other has only 3 going inward, the charge with 12 field lines must be larger. Therefore, it is not possible for the larger charge to be 100 nC. The only option left is for the larger charge to be -100 nC, and the smaller charge to be 25 nC. This configuration would result in 12 field lines going out from the positive charge and 3 going into the negative charge. Therefore, the answer is choice C, -25 nC (the smaller charge with 3 field lines going into it).

In a Diagram of Charges and Electric Field Lines Charge