I've had lots of positive feedback from the "just the facts" series of posts. Yesterday, my colleague Erik Born asked me if I had such a list of facts for waves and optics. I've done optics before, at this post. But I'd not written up waves.
Below are the fundamental facts of physics that Woodberry Honors Physics students need to know for the national Honors Physics exam. These are all also correct for the AP Physics B exam, but AP B adds in standing waves, and quantitative interference/diffraction for slits and thin films. I think this is accurate for the New York Regents exam as well; please, New York folks, let me know if I'm missing something.
Enjoy!
Regarding waves, you need to know:
Definition
of wavelength, amplitude, frequency, period
v = lf
The
speed of a wave depends on the material through which it travels.
When a
wave changes materials, the frequency doesn’t change.
Longitudinal
waves have particles that vibrate parallel to the wave velocity; transverse
waves have particles vibrating perpendicular to the wave velocity.
Sound is
a longitudinal wave that moves about 340 m/s through air.
The
loudness of a sound is related to the wave’s amplitude; the pitch of a sound is
related to the wave’s frequency.
Electromagnetic
waves are transverse waves that move through a vacuum, or air, at 3 x 108
m/s. Visible light is an
electromagnetic wave with wavelength in a vacuum of about 400-700 nm.
The
brightness of light is related to the wave’s amplitude; the color of light is
related to the waves’s frequency.
Electromagnetic
waves with frequency lower than visible light are called infrared, microwave,
and radio. Electromagnetic waves with
frequency higher than visible light are called ultraviolet, x-rays, and gamma
rays.
The
index of refraction n is defined as c/v : the speed of light in a vacuum
divided by the speed of light in a material.
When two
waves collide, they interfere constructively and/or destructively. The colliding waves’ amplitudes add
algebraically.
Two
waves whose frequencies are close together will produce a “beat frequency”
equal to the difference between the two waves’ frequencies.
The
Doppler effect means that a wave source approaching an observer increases the
observed frequency; a source receding from an observer decreases the observed
frequency.
Refraction
is the bending of a wave at a boundary due to the speed change.
Diffraction
is the bending of a wave around an obstacle, which happens when an obstacle is
about a wavelength in size.
Hi Greg,
ReplyDeleteWhat about resonance in a closed/open-ended tube? Do you teach this for AP B?
Yeah, good call... Although it's not on the equation sheet, it's worth knowing that
ReplyDelete* On a string or an open pipe, the fundamental frequency is v/2L, and any multiple of the fundamental can also be played.
* On a closed pipe, the fundamental frequency is v/4L, and only odd multiples of the fundamental can be played.