Question

1. Suppose you have two electrical charges with equal magnitude, but you don't know what the sign of their charge is. As you bring them closer, you notice the electric potential energy between them increases. What can you determine about the sign of each charge? Suppose you have two electrical charges with equal magnitude, but you don't know what the sign of their charge is. As you bring them closer, you notice the electric potential energy between them increases. What can you determine about the sign of each charge?

A. The charges have the same sign

B. Impossible scenario; energy remains constant

C. None of the above

D The charges have opposite sign

Which of the following statements is true about parallel plate capacitors?

2. Which of the following statements is true about parallel plate capacitors?

A. Capacitors charge by AC current

B. Capacitors dissipate energy by allowing current to flow through them

C. Capacitors can be made of two plates separated by a conducting medium

D. If one plate has a charge of +Q, the other plate must have a charge of -Q

How should the distance, D, between two point charges, q₁ and q₂, be changed to double their electric potential energy?

3. How should the distance, D, between two point charges, q₁ and q₂, be changed to double their electric potential energy?

A. D/2

B. D/8

C. D/4

D. 4D

Answer 1

1. Answer: A. The charges have same sign

Explanation: Electrical potential energy(U) of two charges having equal magnitude and having same sign is  given by

where q is magnitude of charge . r = distance between charges . is permittivity of free space.

now from above relation it is clear that if we decrease then the electrical potential energy will increase.

As in the question the potential energy increase as we bring the charges closer so the charges must have same sign.

2. Answer: D. If one plate has a charge of +Q, the other plate must have a charge of -Q

Explanation: For a parallel plate capacitor the two plates must have equal and opposite charge. So if one plate has a charge of +Q, the other plate must have a charge of -Q.

3. Answer: A. D/2

Explanation:

Electric potential energy of two charges q₁ and q₂ and having distance between them D is given by

so it is clear that potential energy is inversely proportional to the distance between the charges(D) .

so to double the potential energy the distance must be half(D/2) the initial distance (D) .

so answer is D/2

Thank You.