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# Physics: Position and magnitude of electric charge

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A +3.0 charge is at and a -1.0 charge is at .
At what point or points on the x-axis is the electric potential zero?
X = ___________ cm

A -2.0 charge and a +2.0 charge are located on the x-axis at and , respectively.
At what position or positions on the x-axis is the electric field zero?
At what position or positions on the x-axis is the electric potential zero?

Estimate the magnitude of the electric field in a cell membrane with a thickness of 8 .

A ion moves from inside a cell, where the electric potential is -70 , to outside the cell, where the potential is 0 .
What is the change in the ion's electric potential energy as it moves from inside to outside the cell?
A 3.0 3.0 parallel-plate capacitor has a 3.0 spacing. The electric field strength inside the capacitor is 1.5×105 .
How much charge is on each plate?

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#### Solution Preview

A +3.0 charge is at and a -1.0 charge is at .
At what point or points on the x-axis is the electric potential zero?
X = ___________ cm

Electric potential at distance r from a point charge q is given by

A) Lat the point is at x = x (x> 4 cm)the potential is zero.
Potential due to positive charge at that point is given by

And field due to negative charge will be

As the net potential at the point will be

Or
Gives 3x - 0.12 = x
Gives x = 0.06 m = 6 cm
B) Lat the point is at x = x (x< 4 cm)the potential is zero.
Potential due to positive charge at that point is given by

And field due to negative charge will be

As the net potential at the point will be

Or
Gives 0.12 -3x = x
Gives x = 0.03 m = 3 cm
Thus the potential is zero at x = 3 cm and x = 6 cm.

A -2.0 charge and a +2.0 charge are ...

#### Solution Summary

The expert examines the position and magnitude of electric charge in physics.

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