AP Physics 2 Quiz: Magnetism And Moving Charges

What this quiz covers

This quiz focuses on Magnetism And Moving Charges, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Physics 2.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

Question 1

1. It is directed upward.
2. It is directed west.
3. It is zero because $\vec{v}$ is parallel to $\vec{B}$. (correct answer)
4. It is directed north (parallel to the velocity).

Explanation: This question tests magnetism and moving charges. The magnetic force F = qv × B depends on the cross product of velocity and magnetic field vectors. When velocity and magnetic field are parallel (both pointing north), their cross product is zero, resulting in zero magnetic force regardless of charge magnitude or sign. This is because sin(0°) = 0 in the formula F = |q|vB sin(θ). Choice D incorrectly suggests force should be parallel to velocity, missing that magnetic forces are always perpendicular. Remember that parallel velocity and field vectors always produce zero magnetic force.

Question 2

1. It is directed upward.
2. It is directed downward. (correct answer)
3. It is directed north (parallel to the velocity).
4. It is zero because the proton is moving at constant speed.

Explanation: This question tests magnetism and moving charges. The magnetic force on a moving charged particle is given by F = qv × B, where the force is perpendicular to both the velocity and magnetic field vectors. For a positive charge moving north with field pointing east, using the right-hand rule: point fingers north (velocity), curl them east (field), and thumb points down. The force is therefore directed downward. Choice C incorrectly assumes force is parallel to velocity, reflecting the misconception that forces always act in the direction of motion. Always use the right-hand rule for positive charges, remembering that magnetic force is perpendicular to both v and B.

Question 3

1. It is directed downward (parallel to the magnetic field).
2. It is directed west. (correct answer)
3. It is directed north (parallel to the velocity).
4. It is directed east.

Explanation: This question tests magnetism and moving charges. The magnetic force direction is determined by F = qv × B, perpendicular to both velocity and field vectors. For positive charge moving north with field downward, apply right-hand rule: fingers north (velocity), curl down (field), thumb points west. The force is therefore directed west. Choice C incorrectly assumes force parallels the magnetic field, violating the fundamental perpendicularity of magnetic forces. Always verify your right-hand rule by checking that F ⊥ v and F ⊥ B.

Question 4

1. It is directed west (parallel to the magnetic field).
2. It is directed downward (parallel to the velocity).
3. It is directed north. (correct answer)
4. It is directed south.

Explanation: This question tests magnetism and moving charges. The magnetic force direction follows F = qv × B, perpendicular to both velocity and field. For velocity downward and field west, the right-hand rule gives force pointing south, but for a negative charge we reverse this to north. The perpendicular relationship ensures force is never parallel to velocity or field. Choice D incorrectly suggests force parallels velocity, a common misconception from everyday forces like friction. For negative charges, use the right-hand rule then flip the result.

Question 5

1. $0\ \text{N}$ because the electron is negative
2. $4.8\times10^{-13}\ \text{N}$
3. $1.2\times10^{-13}\ \text{N}$ (correct answer)
4. $2.4\times10^{-13}\ \text{N}$

Explanation: This question tests magnetism and moving charges. The magnetic force magnitude is F = |q|vB sin(θ), where θ is the angle between velocity and field. With θ = 30°, sin(30°) = 0.5, giving F = (1.60 × 10^-19 C)(3.0 × $10^6$ m/s)(0.50 T)(0.5) = 1.2 × 10^-13 N. The electron's negative charge affects direction but not magnitude. Choice A incorrectly assumes negative charges experience no magnetic force, confusing charge sign effects on direction versus magnitude. Always include sin(θ) when velocity and field aren't perpendicular.

Question 6

1. It is directed west.
2. It is zero because the field is uniform.
3. It is directed north.
4. It is directed east. (correct answer)

Explanation: This question tests understanding of magnetism and moving charges. The magnetic force F = qv × B acts perpendicular to both the particle's velocity and the magnetic field direction. Using the right-hand rule: fingers point north (velocity), curl downward (field direction), thumb points west for a positive charge. Since this particle has negative charge (-1.5 μC), we reverse the direction, making the force point east. Choice D incorrectly suggests uniform fields produce no force, confusing field uniformity with the perpendicular relationship between v and B that determines force. Always apply the right-hand rule for positive charges first, then reverse for negative charges.

Question 7

1. The force is upward.
2. The force is downward. (correct answer)
3. The force is zero because the particle is moving.
4. The force is northward.

Explanation: This problem tests understanding of magnetism and moving charges. The magnetic force is perpendicular to both velocity and magnetic field, following F = qv × B. Using the right-hand rule: point fingers north (velocity), curl them east (field), and your thumb points downward for a positive charge. Since the particle has positive charge (+4.0μC), the force is downward as calculated. Choice D shows the misconception that moving particles experience no magnetic force, when actually only particles at rest or moving parallel to B experience zero force. Remember to apply the right-hand rule systematically: fingers along v, curl toward B, thumb shows F for positive charges.

Question 8

1. The force is upward. (correct answer)
2. The force is northward.
3. The force is eastward.
4. The force is zero because the proton is moving.

Explanation: This problem tests understanding of magnetism and moving charges. The magnetic force on a moving charged particle is given by F = qv × B, where the force is perpendicular to both the velocity and magnetic field vectors. Using the right-hand rule: point your fingers east (velocity direction), curl them north (field direction), and your thumb points upward for a positive charge. Since the proton has positive charge, the force is indeed upward. Choice D incorrectly assumes that moving charges experience no magnetic force, confusing this with the fact that stationary charges experience no magnetic force. To solve these problems systematically, use the right-hand rule for positive charges, then reverse the direction for negative charges.

Question 9

1. The force is northward.
2. The force is eastward. (correct answer)
3. The force is upward.
4. The force is zero because the positron is moving.

Explanation: This problem tests understanding of magnetism and moving charges. The magnetic force is perpendicular to both the velocity and magnetic field vectors, calculated using F = qv × B. Using the right-hand rule: point fingers north (velocity), curl them upward (field), and your thumb points east for a positive charge. Since a positron has positive charge like a proton, the force is eastward. Choice D incorrectly assumes that any moving charged particle experiences no force, confusing this with the condition that only parallel motion to the field produces zero force. To solve these problems, systematically apply the right-hand rule for positive charges, keeping the same direction for positrons.

Question 10

1. $2.4\times10^{-3}\,\text{N}$ (correct answer)
2. $0\,\text{N}$
3. $3.8\times10^{-9}\,\text{N}$
4. $2.4\times10^{3}\,\text{N}$

Explanation: This problem tests magnetism and moving charges. The magnetic force magnitude is F = |q|vB sin θ, where θ is the angle between velocity and field. With velocity north and field downward, they are perpendicular (θ = 90°), so sin θ = 1. Calculating: F = (3.0×10⁻⁶ C)(1.0×10³ m/s)(0.80 T)(1) = 2.4×10⁻³ N. Choice B incorrectly assumes perpendicular vectors produce zero force, when this configuration actually produces maximum force. When solving for magnetic force magnitude, always check the angle between v and B: perpendicular gives maximum force, parallel gives zero force.

Question 11

1. Upward (out of the ground).
2. Due west, because the force is parallel to the velocity.
3. Downward (into the ground). (correct answer)
4. Zero, because the magnetic field is horizontal.

Explanation: This question tests understanding of magnetism and moving charges. The magnetic force F = qv × B must be perpendicular to both velocity and field vectors. For a positive charge moving west with field pointing south, apply the right-hand rule: fingers west (velocity), curl south (field), thumb points downward into the ground. Since this is a positive charge, the force direction is exactly what the right-hand rule gives. Choice C incorrectly assumes force is parallel to velocity, when magnetic forces are always perpendicular to motion. Use the right-hand rule consistently, remembering that the force is always perpendicular to both v and B.

Question 12

1. The force points upward (out of the ground). (correct answer)
2. The force points due east (parallel to the velocity).
3. The force is zero because the proton is moving at constant speed.
4. The force points downward (into the ground).

Explanation: This question tests understanding of magnetism and moving charges. The magnetic force on a charged particle is given by F = qv × B, which is perpendicular to both the velocity vector and the magnetic field vector. For a positive charge moving east with the field pointing north, we apply the right-hand rule: point fingers east (velocity direction), curl them north (field direction), and the thumb points upward out of the ground. Since the proton is positively charged, the force direction from the right-hand rule is the actual force direction. Choice C incorrectly assumes that constant speed means zero force, confusing the fact that magnetic force is always perpendicular to velocity and thus does no work. To solve these problems systematically, use the right-hand rule for positive charges, then reverse the direction if the charge is negative.

Question 13

1. Into the page. (correct answer)
2. To the right, because the force is parallel to the velocity.
3. Out of the page.
4. Zero, because the particle's speed is constant.

Explanation: This question tests understanding of magnetism and moving charges. The magnetic force F = qv × B must be perpendicular to both velocity and magnetic field vectors. For a particle moving right with field pointing upward, the right-hand rule gives: fingers right (velocity), curl upward (field), thumb points out of the page. However, this particle has negative charge, so we reverse the direction—the force points into the page. Choice C incorrectly assumes the force is parallel to velocity, when magnetic forces are always perpendicular to the motion. Remember to always check the sign of the charge and reverse the right-hand rule result for negative charges.

Question 14

1. It is directed sideways, perpendicular to the field.
2. It is zero because the particle is not moving. (correct answer)
3. It is directed upward.
4. It is directed downward.

Explanation: This question tests understanding of magnetism and moving charges. The magnetic force is given by F = qv × B, where v is the particle's velocity. When a particle is at rest, its velocity v = 0, making the entire force expression equal to zero regardless of charge magnitude or field strength. This is fundamentally different from electric forces, which act on stationary charges. Choice D suggests there's always a perpendicular force, missing that velocity is required for magnetic force to exist. Remember that magnetic forces only act on moving charges; stationary charges experience no magnetic force even in the strongest fields.

Question 15

1. It is directed east (parallel to the velocity).
2. It is directed north.
3. It is directed south. (correct answer)
4. It is zero because the charge is negative.

Explanation: This question tests magnetism and moving charges. The magnetic force F = qv × B is perpendicular to both velocity and magnetic field, with direction determined by the cross product. For the electron moving east with field upward, the right-hand rule gives force pointing north, but since the electron is negative, we reverse this to get south. The magnitude is |F| = |q|vB sin(90°) = 1.28 × 10^-13 N. Choice C incorrectly suggests force is parallel to velocity, a common misconception from everyday experience with contact forces. For negative charges, apply the right-hand rule then reverse the direction.

Question 16

1. It is directed east (parallel to the velocity).
2. It is directed upward. (correct answer)
3. It is directed downward.
4. It is zero because the proton is positively charged.

Explanation: This question tests magnetism and moving charges. The magnetic force direction is found using F = qv × B, where the cross product determines perpendicularity. For a proton moving east with field pointing north, apply the right-hand rule: fingers east (velocity), curl north (field), thumb points up. Since the proton is positive, the force is upward. Choice C incorrectly assumes force acts along velocity direction, a misconception from everyday pushing/pulling experiences. Use the right-hand rule systematically: fingers along v, curl toward B, thumb shows F for positive charges.

Question 17

1. It is nonzero and perpendicular to the magnetic field.
2. It is $8.0\times10^{-7}\ \text{N}$ upward.
3. It is $8.0\times10^{-7}\ \text{N}$ downward.
4. It is zero because the particle's speed is zero. (correct answer)

Explanation: This question tests magnetism and moving charges. The magnetic force is F = qv × B, which requires the charge to have velocity relative to the magnetic field. When a particle is at rest (v = 0), the magnetic force is exactly zero regardless of charge magnitude or field strength. This fundamental principle distinguishes magnetic from electric forces. Choice D incorrectly suggests a stationary charge experiences magnetic force, confusing magnetic and electric field effects. Remember: no motion means no magnetic force, distinguishing magnetism from electrostatics.

Question 18

1. It is directed east.
2. It is directed north.
3. It is zero because the particle is moving.
4. It is directed south. (correct answer)

Explanation: This question tests understanding of magnetism and moving charges. The magnetic force on a charged particle is given by F = qv × B, where the force is perpendicular to both the velocity and magnetic field vectors. Using the right-hand rule: point fingers east (velocity direction), curl them upward (field direction), and the thumb points south for a positive charge. Since we have a positive charge (+2.0 μC), the force is directed south. Choice D incorrectly assumes moving particles experience no magnetic force, confusing the condition for zero force (when v is parallel to B) with general motion. To solve these problems systematically, use the right-hand rule for positive charges, then reverse the direction for negative charges.

Question 19

1. The force is downward.
2. The force is eastward. (correct answer)
3. The force is southward.
4. The force is zero because the velocity is perpendicular to the field.

Explanation: This problem tests understanding of magnetism and moving charges. The magnetic force follows F = qv × B and is perpendicular to both velocity and magnetic field directions. Using the right-hand rule: point fingers south (velocity), curl them downward (field), and your thumb points east for a positive charge. Since the particle has positive charge, the force is eastward as calculated. Choice D incorrectly assumes that perpendicular velocity and field result in zero force, when actually this configuration produces maximum force. To solve magnetic force problems, always use the right-hand rule systematically, remembering that the force is perpendicular to both v and B.

Question 20

1. The force is downward.
2. The force is zero because the charge is negative.
3. The force is westward.
4. The force is eastward. (correct answer)

Explanation: This problem tests understanding of magnetism and moving charges. The magnetic force follows F = qv × B and is perpendicular to both velocity and field vectors. Using the right-hand rule: point fingers downward (velocity), curl them south (field), and your thumb points west for a positive charge. Since this particle has negative charge (-2.0μC), we reverse the direction, making the force point east. Choice D incorrectly assumes negative charges experience no magnetic force, when they actually experience force opposite to positive charges. For magnetic force problems, always apply the right-hand rule first for positive charges, then flip the direction for negative charges.