General Physics II (Electricity & Magnetism) – Midterm
PHYS 2002 – MIDTERM EXAM WITH WILLIAM MCELGIN
QUESTIONS AND CORRECT ANSWERS | 2026/2027
PHYS 2002 Midterm Exam with William McElgin
1. A glass rod rubbed with silk becomes positively charged. Which statement
best explains this?
A. Positive charge is created by friction on the glass surface
B. Protons are transferred from the silk to the glass
C. Electrons are transferred from the silk to the glass
D. Electrons are transferred from the glass to the silk
D. Electrons are transferred from the glass to the silk
Rubbing only moves electrons; the glass loses electrons to the silk and is left
with a net positive charge.
2. How many electrons must be removed from a neutral object to give it a net
charge of +3.2 µC?
A. 5.1 × 10¹²
B. 2.0 × 10¹³
C. 5.0 × 10¹⁴
D. 2.0 × 10¹⁰
B. 2.0 × 10¹³
n = Q/e = (3.2 × 10⁻⁶ C)/(1.6 × 10⁻¹⁹ C) = 2.0 × 10¹³ electrons.
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, General Physics II (Electricity & Magnetism) – Midterm
3. Two identical metal spheres carrying +8.0 µC and −2.0 µC are touched
together and then separated. What is the final charge on each sphere?
A. +4.0 µC on one and +2.0 µC on the other
B. +6.0 µC
C. +3.0 µC
D. +5.0 µC
C. +3.0 µC
The total charge (+6.0 µC) is shared equally between identical conductors,
giving +3.0 µC each.
4. The statement that electric charge is quantized means that:
A. Any observable charge is an integer multiple of the elementary charge e
B. Charge can take any continuous value
C. Only electrons can carry charge
D. Charge can never be created or destroyed
A. Any observable charge is an integer multiple of the elementary charge e
Free charges always appear in whole-number multiples of e = 1.6 × 10⁻¹⁹ C.
5. A positively charged rod is held near a neutral metal sphere that is
connected to ground. The ground wire is removed, and then the rod is taken
away. The sphere is now:
A. Neutral
B. Positively charged
C. Polarized but with zero net charge
D. Negatively charged
D. Negatively charged
Electrons flow up from ground toward the rod; cutting the ground first traps
them, leaving the sphere negative by induction.
6. A rubbed balloon sticks to a neutral wall because:
A. Air pressure pushes the balloon against the wall
B. Gravity is cancelled by the electric field of the balloon
C. Molecules in the wall become polarized, placing opposite charge closer to
the balloon
D. The wall acquires a net charge opposite to the balloon
C. Molecules in the wall become polarized, placing opposite charge closer
to the balloon
Polarization puts the attracting charges nearer than the repelling ones, so the net
force is attractive.
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, General Physics II (Electricity & Magnetism) – Midterm
7. The law of conservation of charge states that:
A. Charge is conserved only in conductors
B. The net charge of an isolated system remains constant
C. Positive and negative charges always exist in equal amounts in every object
D. The number of electrons in an object never changes
B. The net charge of an isolated system remains constant
Charge can be transferred but the algebraic total in an isolated system never
changes.
8. When a charged rod is brought near (but not touching) the top of an
uncharged electroscope, the leaves spread apart because:
A. The leaves become oppositely charged and attract the case
B. The leaves acquire like charges by induction and repel each other
C. The leaves gain charge directly from the rod
D. Air molecules between the leaves are ionized
B. The leaves acquire like charges by induction and repel each other
Charge separation pushes like charge down to both leaves, which then repel.
9. Which of the following materials is the best electrical conductor?
A. Copper
B. Dry wood
C. Rubber
D. Glass
A. Copper
Copper has many loosely bound valence electrons that move freely through the
lattice.
10. Three identical conducting spheres A, B and C carry +12 µC, 0 and 0
respectively. A touches B and is separated, then A touches C and is separated.
What is the final charge on A?
A. +6.0 µC
B. +3.0 µC
C. +1.5 µC
D. +4.0 µC
B. +3.0 µC
A and B share to +6 µC each; A and C then share +6 µC to give +3.0 µC each.
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, General Physics II (Electricity & Magnetism) – Midterm
SECTION B: COULOMB'S LAW
11. Two point charges, +2.0 µC and +3.0 µC, are 0.30 m apart. What is the
force between them?
A. 0.60 N, repulsive
B. 0.18 N, repulsive
C. 1.8 N, repulsive
D. 0.60 N, attractive
A. 0.60 N, repulsive
F = kq₁q₂/r² = (9.0 × 10⁹)(2.0 × 10⁻⁶)(3.0 × 10⁻⁶)/(0.30)² = 0.60 N; like charges
repel.
12. If the distance between two point charges is tripled, the electrostatic force
between them becomes:
A. 3F
B. 9F
C. F/3
D. F/9
D. F/9
Coulomb force is inverse-square, so tripling r reduces F by 3² = 9.
13. Both charges in a pair are doubled and their separation is also doubled.
The new force compared with the original is:
A. Doubled
B. Halved
C. Four times larger
D. Unchanged
D. Unchanged
The numerator grows by 4 and the denominator by 4, so F stays the same.
14. In a hydrogen atom the electron and proton are about 5.3 × 10⁻¹¹ m apart.
The magnitude of the electric force between them is approximately:
A. 2.3 × 10⁻²⁸ N
B. 8.2 × 10⁻⁸ N
C. 1.5 × 10⁻⁹ N
D. 4.3 × 10⁻¹⁸ N
B. 8.2 × 10⁻⁸ N
F = k e²/r² = (9.0 × 10⁹)(1.6 × 10⁻¹⁹)²/(5.3 × 10⁻¹¹)² ≈ 8.2 × 10⁻⁸ N.
Page 4 of 51
PHYS 2002 – MIDTERM EXAM WITH WILLIAM MCELGIN
QUESTIONS AND CORRECT ANSWERS | 2026/2027
PHYS 2002 Midterm Exam with William McElgin
1. A glass rod rubbed with silk becomes positively charged. Which statement
best explains this?
A. Positive charge is created by friction on the glass surface
B. Protons are transferred from the silk to the glass
C. Electrons are transferred from the silk to the glass
D. Electrons are transferred from the glass to the silk
D. Electrons are transferred from the glass to the silk
Rubbing only moves electrons; the glass loses electrons to the silk and is left
with a net positive charge.
2. How many electrons must be removed from a neutral object to give it a net
charge of +3.2 µC?
A. 5.1 × 10¹²
B. 2.0 × 10¹³
C. 5.0 × 10¹⁴
D. 2.0 × 10¹⁰
B. 2.0 × 10¹³
n = Q/e = (3.2 × 10⁻⁶ C)/(1.6 × 10⁻¹⁹ C) = 2.0 × 10¹³ electrons.
Page 1 of 51
, General Physics II (Electricity & Magnetism) – Midterm
3. Two identical metal spheres carrying +8.0 µC and −2.0 µC are touched
together and then separated. What is the final charge on each sphere?
A. +4.0 µC on one and +2.0 µC on the other
B. +6.0 µC
C. +3.0 µC
D. +5.0 µC
C. +3.0 µC
The total charge (+6.0 µC) is shared equally between identical conductors,
giving +3.0 µC each.
4. The statement that electric charge is quantized means that:
A. Any observable charge is an integer multiple of the elementary charge e
B. Charge can take any continuous value
C. Only electrons can carry charge
D. Charge can never be created or destroyed
A. Any observable charge is an integer multiple of the elementary charge e
Free charges always appear in whole-number multiples of e = 1.6 × 10⁻¹⁹ C.
5. A positively charged rod is held near a neutral metal sphere that is
connected to ground. The ground wire is removed, and then the rod is taken
away. The sphere is now:
A. Neutral
B. Positively charged
C. Polarized but with zero net charge
D. Negatively charged
D. Negatively charged
Electrons flow up from ground toward the rod; cutting the ground first traps
them, leaving the sphere negative by induction.
6. A rubbed balloon sticks to a neutral wall because:
A. Air pressure pushes the balloon against the wall
B. Gravity is cancelled by the electric field of the balloon
C. Molecules in the wall become polarized, placing opposite charge closer to
the balloon
D. The wall acquires a net charge opposite to the balloon
C. Molecules in the wall become polarized, placing opposite charge closer
to the balloon
Polarization puts the attracting charges nearer than the repelling ones, so the net
force is attractive.
Page 2 of 51
, General Physics II (Electricity & Magnetism) – Midterm
7. The law of conservation of charge states that:
A. Charge is conserved only in conductors
B. The net charge of an isolated system remains constant
C. Positive and negative charges always exist in equal amounts in every object
D. The number of electrons in an object never changes
B. The net charge of an isolated system remains constant
Charge can be transferred but the algebraic total in an isolated system never
changes.
8. When a charged rod is brought near (but not touching) the top of an
uncharged electroscope, the leaves spread apart because:
A. The leaves become oppositely charged and attract the case
B. The leaves acquire like charges by induction and repel each other
C. The leaves gain charge directly from the rod
D. Air molecules between the leaves are ionized
B. The leaves acquire like charges by induction and repel each other
Charge separation pushes like charge down to both leaves, which then repel.
9. Which of the following materials is the best electrical conductor?
A. Copper
B. Dry wood
C. Rubber
D. Glass
A. Copper
Copper has many loosely bound valence electrons that move freely through the
lattice.
10. Three identical conducting spheres A, B and C carry +12 µC, 0 and 0
respectively. A touches B and is separated, then A touches C and is separated.
What is the final charge on A?
A. +6.0 µC
B. +3.0 µC
C. +1.5 µC
D. +4.0 µC
B. +3.0 µC
A and B share to +6 µC each; A and C then share +6 µC to give +3.0 µC each.
Page 3 of 51
, General Physics II (Electricity & Magnetism) – Midterm
SECTION B: COULOMB'S LAW
11. Two point charges, +2.0 µC and +3.0 µC, are 0.30 m apart. What is the
force between them?
A. 0.60 N, repulsive
B. 0.18 N, repulsive
C. 1.8 N, repulsive
D. 0.60 N, attractive
A. 0.60 N, repulsive
F = kq₁q₂/r² = (9.0 × 10⁹)(2.0 × 10⁻⁶)(3.0 × 10⁻⁶)/(0.30)² = 0.60 N; like charges
repel.
12. If the distance between two point charges is tripled, the electrostatic force
between them becomes:
A. 3F
B. 9F
C. F/3
D. F/9
D. F/9
Coulomb force is inverse-square, so tripling r reduces F by 3² = 9.
13. Both charges in a pair are doubled and their separation is also doubled.
The new force compared with the original is:
A. Doubled
B. Halved
C. Four times larger
D. Unchanged
D. Unchanged
The numerator grows by 4 and the denominator by 4, so F stays the same.
14. In a hydrogen atom the electron and proton are about 5.3 × 10⁻¹¹ m apart.
The magnitude of the electric force between them is approximately:
A. 2.3 × 10⁻²⁸ N
B. 8.2 × 10⁻⁸ N
C. 1.5 × 10⁻⁹ N
D. 4.3 × 10⁻¹⁸ N
B. 8.2 × 10⁻⁸ N
F = k e²/r² = (9.0 × 10⁹)(1.6 × 10⁻¹⁹)²/(5.3 × 10⁻¹¹)² ≈ 8.2 × 10⁻⁸ N.
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