Update
Yeah, I got lazy. I realized that the AP Physics II exam is not that hard. It’s time to focus on programming LOL.
Overview
There are 7 units in this course.
- Unit 9: Thermodynamics
- Unit 10: Electric Force, Field, and Potential
- Unit 11: Electric Circuits
- Unit 12: Magnetism and Electromagnetism
- Unit 13: Geometric Optics
- Unit 14: Waves, Sound, and Physical Optics
- Unit 15: Modern Physics
Resources I Have
For individual units, I have the Albert practice, of which I will probably redo the topic that I miss the most on the practice exam. I think I should attend the review session this weekend and just do a mock exam.
Schedules
April 16th, 2025
- I am reviewing Electromagnetism by going over the Course and Exam Descriptions 2024.
Units
Unit 12: Magnetism and Electromagnetism
- Albert #4 Electromagnetism
Core Concepts
- Relationships between moving charges, the magnetic fields they generate, and the magnetic forces that act on other moving charges in those fields.
- Students are to explain the steps that lead from the equation, law, or physical principle to the justification of their claim on the FRQ.
Right Hand Rules
Moving Charges/Current in a wire affected by magnetic field - e.g. magnetic force on moving charges
When charges are sitting still, they are unaffected by magnetic fields. As soon as they begin to move, the magnetic field pushes on them. To use this mnemonic: your index finger is the direction of the moving charge, your middle finger is the magnetic field/field lines, and your thumb is the magnetic force, F.
F is the direction of the force that will be applied to the moving charge. In this question,
Magnetic Field caused by current in a wire (nothing about force)
Thumb and wrap your hand around a wire. This right hand rule is also used in this problem but it’s given to you. The magnetic field is either in or out depending on which side of the wire you’re on.
12.1 Magnetic Fields
- Understand the Right Hand rule: for moving charge, along a current wire.
- Understand magnets: magnetization, dipoles, magnetic domains, magnetic field alignment. Magnets go from North to South on the outside and South to North on the inside. Outside a magnetic field, magnetic domains magnetized point to the South, while inside a magnetic field, it points to North.
- Magnetic field is a vector field - produced by magnetic dipoles or combination thereof but never by monopole. It forms closed loop. As well, South never exists without North and vice versa. There’s always a dipole for magnetic fields.
- Magnetic behavior of a material: dipoles result from the circular or rotational motion of electric charges: the motion of electrons. Permanent magnetism and incuded magnetism are system properties that both result from the alignment of magnetic dipoles within a system.
- Material composition: ferromagnetic materials like iron, nickel, cobalt are permanently magnetized by an external field; paramagnetic materials such as aluminum, titanium, and magnesium interact weakly with an external magnetic field but then doesn’t after the field is removed.
- Magnetic permeability: a measurement of the amount of magnetization in a material in response to an external magnetic field. A higher magnetic permeability means higher occurence of a material changing its magnetic properties. For example, iron has high permeability.
12.2 Magnetism and Moving Charges
- Moving charge and magnetic field: a single moving charge object produces a magnetic field. The magnetic field at a particular point produced by a moving charged object depends on the object’s velocity and distance between the point and the object.
- The magnitude of a magnetic field is maxmimum when the velocity vector and the position vector from that object to the point in space are perpendicular.
- Know \(F_b = qvB\sin{\theta}\). The magnetic force is porportional to q, v, B. It is at the maximum when \(\theta = 90^{o}\).
- The Hall Effect: the potential difference created in a conductor by an external magnetic field that has a component perpendicular to the direction of charges moving in the conductor. TLDR: electrons moving, starts moving in another direction because of magnetic force from its interaction with a magnetic field. Then electrons create potential with the other side that lacks negative charge in a conductor/conducting material.
12.3 Magnetism and Current-Carrying Wire
- \(B = \frac{\mu_o I}{2\pi r}\). Ampere’s Law.
- \(F_B = BI\ell\sin{\theta{}}\). Finding the magnetic force along a current carrying wire.
12.4: Electromagnetic Induction and Faraday’s Law
- Magnetic flux: amount of the component of a magnetic field that is perpendicular to a cross-sectional area.
- \(\Phi_B = BA\cos{\theta}\). \(\Phi_B\) is the magnetic flux; it is proportional to \(B\), the component of the magnetic field perpendicular to the surface, and \(A\), the cross-sectional area of the surface.
- The area vector is defined to be perpendicular to the plane of the surface and directed outward from a closed surface.
- The sign of a magnetic flux indicates whether the magnetic field is parallel to or antiparallel to the area vector.
- \(|\mathcal{E}| = |\frac{\Delta\Phi_B}{\Delta t}|\) Faraday’s Law: changing magnetic flux and induced \(\mathcal{E}\). Magnetic field have to change for there to be induced \(\mathcal{E}\) and therefore current.
- \(\mathcal{E} = -\frac{\Delta \Phi_B}{\Delta t} = \frac{\Delta(BA\cos{\theta})}{\Delta t}\) Lenz’s Law: Determining the direction of an induced \(\mathcal{E}\). resulting from a changing \(\Phi_B\).
- An induced \(\mathcal{E}\) generates a current that creates a magnetic field that opposes the change in \(\Phi_B\). You can also use the right-hand rule to determine the relatioship between current, \(\mathcal{E}\), and \(\Phi_B\).
- \(\mathcal{E} = B\ell v\). Common equation.
- An example of electromagnetic induction: conducting rod on conducting rails in a region with uniform magnetic field.