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+q . . . . . . . . . . . . . . . . -q |<--------- d ---------->| Two charges +q

ID: 1624045 • Letter: #

Question

+q . . . . . . . . . . . . . . . . -q
|<--------- d ---------->|

Two charges +q and -q are at distance d apart, as indicated above, and the force between them has magnitude F.

The left hand charge is now doubled and made negative, becoming -2q, and the right hand charge remains the same, at the same position.

Which of the following best describes the forces now, in terms of the original force F?

Select one:

a. Force on the left hand charge is 2F to the left and the force on the right hand charge is 2F to the right.

b. Force on left-hand charge is 2F to the right and the force on the right-hand charge is F to the left.

c. Force on left-hand charge is 2F to the left and the force on the right hand charge is F to the left.

d. Force on left-hand charge is 2F to the right and the force on the right-hand charge is 2F to the left.

e. Force on left-hand charge is 2F to the right and the force on the right-hand charge is 2F to the right.

Which ONE of the following is INCORRECT?

Select one:

a. If one K+ leaves the cell and one Na+ enters at the same time, membrane potential will remain the same

b. If many K+ channels AND many Na+ channels were open at rest, the cell would find it difficult to maintain a resting membrane potential

c. Due to the relatively large number of open K+ channels, the number of K+ entering the cell equals the number of K+ leaving the cell

d. If a K+ leaves the cell, the inside of the cell becomes a little more negative.

e. The urge for Na+ to enter the cell is very great – both concentration gradient and membrane potential attracts Na+ entry

Explanation / Answer

Force two chareged particles is

F= kq2 / r2

since the magnitude of charge on the left is doubles, the force on left is 2F to the right and the force on right is F to the left.

Answer is 'b'