Practice Questions & Helpful Sites

Recommended: SparkNotes test prep: SAT Physics.

This is a good summary of the key concepts, though it's not AP level, it's a good way to see if you've got the basics down. This includes practice multiple choice questions and examples for each section. It has sections for EMF, waves, and pretty much everything other chapter needed for the AP Exam. You can select which section in the top blue bar.

Wave Objectives.

A lot of the AP objectives for waves were fairly simple. Review them to refresh you mind about basic wave properties and behaviors.

Inverse- square Law for Light A better explanation of this law and how to use it.

Tricks

Right hand rule- Used for protons.

Right Hand Rule #1

Right Hand Rule #2

Magnetic field in a wire

Left Hand for electrons- Since the right hand rule gives us the direction of positive charges, use the left hand in the same manner as the right to get the flow of electrons

Important concepts

Chapter 22 - Electromagnetic Induction

EMF stands for electromotive force.
An emf can be induced in a wire or coil of wire with a magnetic field.
Emf can also be induced by changing the area of a coil in a constant magnetic field.
Induced EMF (voltage) resulting from these changes cause a current to flow. This is the induced current - brought about by a change in magnetic field OR any current resulting from the EMF.
(page 680-81) 

Motional emf arises when a charged conductor is moving through a magnetic field. It arises due magnetic forces (the potential difference caused by the electric field) on charges moving through a magnetic field. If the rod is not moving, there is no motional emf.
(page 682-83)

Ɛ = vBL

Magnetic Flux

Φ = BA cosθ

Thus: three ways to change the magnetic flux are

1. Change the area
2. Change the magnetic field strength
3. Change the angle between the magnetic field and the area

 The magnetic flux is proportional to the number of field lines that pass through a surface (pg 688)

 Faraday's Law of Electromagnetic Induction

 Ɛ = -N(ΔΦ/Δt)
This equation gives us the average emf induced in a coil with N loops. This law states that an emf is generated if the magnetic flux changes for any of the three reasons above. (pg 689)

Lenz's Law

The induced emf resulting from a change in magnetic flux leads to an induced current whose direction is such that the induced magnetic field opposes the original flux change. (This uses RHR-2 : see Tricks) (pg 692)

Helpful: Conceptual Example 9 pg 693

Chapter 16 & 17 - Waves

Waves carry energy from place to place.
Properties:
Amplitude - The maximum displacement of a wave
Wavelength - The distance between two crests, troughs, etc.
Frequency - How many cycles per second (Hertz, Hz)
Wave types:
Longitudinal - i.e Sound waves. Oscillation is parallel to direction.
Transverse - Oscillation is perpendicular to direction of movement. Can experience polarization.

 

The Doppler Effect

The change in frequency or pitch of sound detected by an observer because the sound source and the observer have different velocities with respect to the medium of sound propagation.
(Pg 489)

Speed of a wave on strings and sound

Strings - a wave travels faster on string with particles of smaller mass (small mass per unit length). Speed also dependent on how fast the string is accelerated. Greater tension also equals faster speed due to the greater pulling force of the string.
Sound - sound can only be transmitted in a medium. The speed of sound thus depends on the medium it's traveling through.

The Inverse-square Law: The intensity of illumination is proportional to the  inverse square of the distance from the light source.   (Click here for more)  

Standing Waves: Occur when two waves overlap when identical waves travel on the string in opposite directions.

• Nodes - points of no vibration
• Anti-nodes - places of maximum vibration

 See the Equations dealing with standing waves.

Principle of Linear Superposition

When two or more waves are present simultaneously at the same place, the resultant is the sum of the disturbances of the individual waves. (pg 507)

Equations

EMF

Equation: Ɛ = vBL

Variables:

• Ɛ - motional EMF (volts, V)
• v - velocity of movement (m/s)
• B - magnetic field (T)
• L - length of rod between rails (m)

Equation: Φ = BA cosθ

Variables: 

• Φ - magnetic flux (webber, Wb OR volts-seconds)
• B - magnetic field (T)
• A - area (m^2)
• θ - Angle between the magnetic field and the area, usually 90 degrees

Equation: Ɛ = -N(ΔΦ/Δt)
Variables:

•  Ɛ - magnitude of induced emf (volts, V)
• ΔΦ - Change in magnetic flux (Wb)
• Δt - Change in time (s)
• N - number of loops (no units)

Waves

Equation: v = fλ
Variables:

• v - velocity of wave (m/s)
• f - frequency (Hz)
• λ - wavelength (m)

Equation: String fixed on both ends

f = n(v/2L)

Variables:

• n - integer (1,2,3...)
• v - wave speed
• L - length of the string

Equation: Tube open on both ends

 f = n (v/2L)

Variables:

• n - integer (1,2,3...)
• v - wave speed
• L - length of the tube (*must be an integer number of n half-wavelengths) 

Equation: Tube closed at one end

f = n(v/4L)

Same variables as above. See pg 520-22 for more information.