# Electric voltage – problems and solutions

1. Determine the electric potential at a point located at 1 cm from a charge 5.0 μC. Coulomb constant (k) = 9 x 109 Nm2C−2, 1 μC = 10−6 C.

Known :

The distance from charge (r) = 1 cm = 1/100 m = 0.01 m = 10-2 m

Charge (q) = 5.0 μC = 5.0 x 10-6 C

Coulomb constant (k) = 9 x 109 Nm2C−2

Wanted : Electric potential (V)

Solution :

Electric potential : Electric potential is 4.5 x 106 Volt

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2. Charge Q1 = 5.0 μC and charge Q2 = 6.0 μC. Coulomb’s constant (k) = 9 x 109 Nm2C−2, 1 μC = 10−6 C. Point A located between the charges. Determine electric potential at point A. Known :

Charge Q1 = -5.0 μC = -5.0 x 10-6 C

The distance of point A from Q1 = 10 cm = 0.1 m = 10-1 m

Charge Q2 = 6.0 μC = 6.0 x 10-6 C

The distance of point a from Q2 = 10 cm = 0.1 m = 10-1 m

Coulomb’s constant (k) = 9 x 109 Nm2C−2

Wanted : Electric potential at point A

Solution :

Electric potential 1 : Electric potential 2 : Electric potential at point A :

V = V2 – V1

V = (54 – 45) x 104

V = 9 x 104

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3. Charge q1 = 5.0 μC and charge q2 = 6.0 μC. Coulomb’s constant (k) = 9 x 109 Nm2C−2, 1 μC = 10−6 C. Determine the electric potential at point A. Known :

Charge Q1 = -5.0 μC = -5.0 x 10-6 C

The distance of point A from Q1 = 40 cm = 0.4 m = 4 x 10-1 m

Charge Q2 = 6.0 μC = 6.0 x 10-6 C

The distance of point A from Q2 = 50 cm = 0.5 m = 5 x 10-1 m

Coulomb’s constant (k) = 9 x 109 Nm2C−2

Wanted : Electric potential at point A

Solution :

Electric potential 1 : Electric potential 2 : Electric potential at point A :

V = V1 + V2

V = (-11.25 + 10.8) x 104

V = -0.45 x 104

V = -4.5 x 103

Electric potential at point A is -4.5 x 103 Volt 