Electric Charges & Fields
Q. A charge of +10μC is placed in a uniform electric field of strength 500 N/C. What is the work done in moving the charge 2m in the direction of the field?
A.
10 J
B.
1 J
C.
100 J
D.
0.5 J
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Solution
Work done W = F * d = (E * q) * d = (500 N/C * 10 × 10^-6 C) * 2m = 0.01 J.
Correct Answer: A — 10 J
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Q. A charge of +10μC is placed in a uniform electric field of strength 500 N/C. What is the work done in moving the charge 0.1m in the direction of the field?
A.
0.5 J
B.
1 J
C.
2 J
D.
0.1 J
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Solution
Work done W = F * d = (E * q) * d = (500 N/C * 10 × 10^-6 C) * 0.1 m = 0.5 J.
Correct Answer: A — 0.5 J
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Q. A charge of +3μC is placed at the origin. What is the electric potential at a point 0.5m away?
A.
5400 V
B.
1800 V
C.
7200 V
D.
3600 V
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Solution
V = k * q / r = (9 × 10^9) * (3 × 10^-6) / 0.5 = 54000 V.
Correct Answer: D — 3600 V
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Q. A charge of +3μC is placed at the origin. What is the potential at a point 0.3m away?
A.
9000 V
B.
3000 V
C.
10000 V
D.
15000 V
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Solution
V = k * q / r = (9 × 10^9 N m²/C²) * (3 × 10^-6 C) / 0.3 m = 9000 V.
Correct Answer: A — 9000 V
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Q. A charge of +3μC is placed in a uniform electric field of strength 1500 N/C. What is the work done in moving the charge 0.2 m in the direction of the field?
A.
90 J
B.
60 J
C.
30 J
D.
45 J
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Solution
Work done W = F * d = (E * q) * d = (1500 N/C * 3 × 10^-6 C) * 0.2 m = 0.0009 J = 90 J.
Correct Answer: B — 60 J
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Q. A charge of +4μC is placed at the origin. What is the electric field at a point 2m away on the x-axis?
A.
0 N/C
B.
450 N/C
C.
900 N/C
D.
1800 N/C
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Solution
E = k * |q| / r^2 = (9 × 10^9) * 4 × 10^-6 / (2)^2 = 450 N/C.
Correct Answer: C — 900 N/C
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Q. A charge of +5μC is placed at the origin. What is the electric field at a point 2m away along the x-axis?
A.
0 N/C
B.
1125 N/C
C.
2250 N/C
D.
4500 N/C
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Solution
E = k * |q| / r² = (9 × 10^9 N m²/C²) * (5 × 10^-6 C) / (2 m)² = 1125 N/C.
Correct Answer: C — 2250 N/C
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Q. A charge of +5μC is placed in an electric field of strength 2000 N/C. What is the force experienced by the charge?
A.
10N
B.
1N
C.
100N
D.
200N
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Solution
Force F = qE = (5 × 10^-6 C) * (2000 N/C) = 10 N.
Correct Answer: A — 10N
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Q. A charge of -2μC is placed in an electric field of 500 N/C. What is the force acting on the charge?
A.
-1 N
B.
1 N
C.
-0.5 N
D.
0.5 N
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Solution
Force F = E * q = 500 N/C * -2 × 10^-6 C = -1 N.
Correct Answer: A — -1 N
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Q. A dipole consists of two charges +q and -q separated by a distance d. What is the expression for the dipole moment?
A.
qd
B.
q/d
C.
q^2d
D.
q/d^2
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Solution
The dipole moment p is defined as p = q * d.
Correct Answer: A — qd
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Q. A dipole consists of two charges +q and -q separated by a distance d. What is the dipole moment?
A.
qd
B.
q/d
C.
q^2d
D.
q/d^2
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Solution
The dipole moment p = q * d.
Correct Answer: A — qd
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Q. A dipole consists of two equal and opposite charges separated by a distance of 0.1m. What is the dipole moment if each charge is 1μC?
A.
1 × 10^-7 C m
B.
1 × 10^-6 C m
C.
1 × 10^-5 C m
D.
1 × 10^-4 C m
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Solution
Dipole moment p = q * d = (1 × 10^-6 C) * (0.1 m) = 1 × 10^-7 C m.
Correct Answer: B — 1 × 10^-6 C m
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Q. A dipole consists of two equal and opposite charges separated by a distance. What happens to the dipole moment if the distance is doubled?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It quadruples
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Solution
Dipole moment p = q * d, if d is doubled, p also doubles.
Correct Answer: A — It doubles
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Q. If a charge of +3μC is placed in a uniform electric field of strength 2000 N/C, what is the force acting on the charge?
A.
6000 N
B.
3000 N
C.
4000 N
D.
2000 N
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Solution
F = qE = (3 × 10^-6 C) * (2000 N/C) = 6 × 10^-3 N = 6000 N.
Correct Answer: A — 6000 N
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Q. If a charge of +3μC is placed in an electric field of 1000 N/C, what is the force acting on it?
A.
3000 N
B.
3 N
C.
0.3 N
D.
30 N
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Solution
F = q * E = (3 × 10^-6 C) * (1000 N/C) = 3 × 10^-3 N = 3000 N.
Correct Answer: A — 3000 N
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Q. If a charge of +3μC is placed in an electric field of 500 N/C, what is the force acting on it?
A.
1500 N
B.
300 N
C.
500 N
D.
750 N
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Solution
F = q * E = (3 × 10^-6 C) * (500 N/C) = 1500 N.
Correct Answer: A — 1500 N
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Q. If a charge of +4μC is placed in an electric field of 500 N/C, what is the force acting on the charge?
A.
2 N
B.
0.5 N
C.
4 N
D.
1 N
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Solution
F = q * E = 4 × 10^-6 C * 500 N/C = 2 N.
Correct Answer: A — 2 N
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Q. If the electric field at a point is 100 N/C and the charge at that point is +5μC, what is the force experienced by the charge?
A.
0.5 N
B.
0.2 N
C.
0.1 N
D.
0.4 N
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Solution
Force F = E * q = 100 N/C * 5 × 10^-6 C = 0.0005 N = 0.5 N.
Correct Answer: A — 0.5 N
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Q. If the electric field at a point is 200 N/C and the charge at that point is +5μC, what is the force experienced by the charge?
A.
0.1 N
B.
1 N
C.
0.5 N
D.
2 N
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Solution
F = E * q = 200 N/C * 5 × 10^-6 C = 1 N.
Correct Answer: B — 1 N
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Q. If the electric field due to a point charge is 1000 N/C at a distance of 1m, what is the charge?
A.
1μC
B.
2μC
C.
3μC
D.
4μC
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Solution
Using E = k * |q| / r^2, we find q = E * r^2 / k = 1000 * 1^2 / (9 × 10^9) = 1μC.
Correct Answer: A — 1μC
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Q. If two identical charges are placed 1 meter apart, what happens to the force between them if the distance is doubled?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It quadruples
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Solution
According to Coulomb's law, force is inversely proportional to the square of the distance. If the distance is doubled, the force becomes one-fourth.
Correct Answer: B — It halves
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Q. If two identical charges are placed 1m apart, what is the electric field at a point midway between them?
A.
0 N/C
B.
kq/2
C.
kq
D.
2kq
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Solution
The electric fields due to both charges at the midpoint cancel each other, resulting in a net electric field of 0.
Correct Answer: A — 0 N/C
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Q. If two identical charges are placed at a distance of 1m apart, what is the electric field at a point midway between them?
A.
0 N/C
B.
kq/2
C.
kq
D.
kq/4
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Solution
The electric fields due to both charges at the midpoint cancel each other, resulting in a net electric field of 0 N/C.
Correct Answer: A — 0 N/C
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Q. If two identical charges are placed at a distance of 1m, what is the potential energy of the system?
A.
0.5 J
B.
1 J
C.
2 J
D.
4 J
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Solution
Potential energy U = k * q1 * q2 / r = (9 × 10^9 N m²/C²) * (q²) / 1m. For q = 1μC, U = 1 J.
Correct Answer: B — 1 J
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Q. In a parallel plate capacitor, if the distance between the plates is halved, what happens to the capacitance?
A.
It halves
B.
It doubles
C.
It remains the same
D.
It quadruples
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Solution
Capacitance C = ε₀ * A / d. If d is halved, C doubles.
Correct Answer: B — It doubles
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Q. In a uniform electric field, the equipotential surfaces are:
A.
Curved
B.
Straight lines
C.
Concentric circles
D.
Parallel planes
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Solution
In a uniform electric field, the equipotential surfaces are parallel planes.
Correct Answer: D — Parallel planes
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Q. Two charges +q and -q are placed at a distance d apart. What is the electric field at the midpoint between the charges?
A.
0
B.
kq/d^2
C.
2kq/d^2
D.
kq/2d^2
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Solution
The electric fields due to both charges at the midpoint cancel each other, resulting in a net electric field of 0.
Correct Answer: A — 0
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Q. Two charges +q and -q are placed at a distance d apart. Where can a third charge be placed such that the net force on it is zero?
A.
At a distance d/2 from +q
B.
At a distance d/2 from -q
C.
At a distance greater than d from both
D.
At a distance less than d/2 from both
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Solution
The third charge must be placed between +q and -q, closer to -q to balance the forces.
Correct Answer: B — At a distance d/2 from -q
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Q. Two charges +q and -q are placed at a distance d apart. Where is the electric field zero?
A.
At the midpoint
B.
Closer to +q
C.
Closer to -q
D.
At infinity
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Solution
The electric field is zero at a point closer to -q because the magnitudes of the fields due to both charges will be equal at that point.
Correct Answer: C — Closer to -q
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Q. What happens to the electric field if the charge is tripled while keeping the distance constant?
A.
It triples
B.
It halves
C.
It remains the same
D.
It quadruples
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Solution
The electric field is directly proportional to the charge. Tripling the charge will triple the electric field.
Correct Answer: A — It triples
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