36 points I Previous Answers My Notes Two point charges, 5.0 uc and -2.0 uc, are

Question

36 points I Previous Answers My Notes Two point charges, 5.0 uc and -2.0 uc, are placed 4.2 cm apart on the x axis, such that the -2.0 uc charge is at x o and the 5.0 uc charge is at 4.2 cm. (a) At what point(s) along the x axis is the electric field zero? (If there is no point where E- 0 in a region, enter "o" in that box.) 0 x 4.2 cm 0 cm 4.2 cm x V cm (b) At what point(s) along the x axis is the potential zero? Let v- o at r co. (If there is no point where v- o in a region, enter in that box.) X

Explanation / Answer

  electric field is the force per unit charge.

The given two charges are oppositely charged . A positive unit charge placed in between them will be repelled by the positive charge of 5 C and hence the force is toward the origin .

The negative charge will attract this unit charge and hence this force is also toward origin.

Hence the unit charge has to be away from both charges so that the net force is zero.


Let the charge be at a distance a from the origin.
Since the forces are equal and opposite

2 / a² = 5 / (a - 4.2) ²

a = 0.20 cm or -5.80 cm from the origin.

Both distances give the point where the field is zero.
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b)Let at a point distant a from the origin the potential is zero.
Then
-2 /a + 5 / ( 4.2 –a) =0

a = 1.2 cm from the origin .

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