Phase, Wavelength, Speed Notes

Speed and Medium for a Wave

A. Phase

"In Phase" (0°) – points on a single periodic wave that have the same displacement (from equilibrium position) and moving in the same direction

Whole number of wavelengths apart

A & ____ A & ____ B & ___ B & ___

A & E, A & I, A & M

B & F, B & J, B & N

"Out of Phase"– (180⁰)

- same displacement from equilibrium position but going in a different direction

½, 1½, 2½ etc wavelengths apart

A & C, B & D, F & H

Which 2 points are in phase?

C and F

2 points that are 180°
out of phase?

B and D

E and G

B. Wavelength – distance between two consecutive points in phase

determined by medium

symbol λ = lambda

Wavelength
St. Mary's Physics Online

- length of one cycle #m/cycle

Ex) Wavelength?

June 2000

λ = 5.0 m/2.5 cycles

λ = 2.0 m

Ex)

Amplitude? Wavelength?

Amplitude = .10 m

Wavelength = .60 m

Ex)

Amplitude A?, B?, C?

Jan 2004

C. Speed – the number of meters a single cycle travels per second

1. V = fλ solve for f:

f = v/λ

inverse relationship

2. Speed of wave depends on the medium

(slower in dense media)

slinkyreflections2.mov

Rutgers University

Speed Of a Mechanical Wave

Monterey Institute

Ex) f = 40. hertz. V = ?

(1) 13 m/s (2) 27 m/s

(3) 60. m/s (4) 120 m/s

Jan 2002 Test

V = fλ

V = 40. Hz(1.5 m)

(3) 60. m/s

3. Velocity sound = 3.3 x 10² m/s

(Air, Reference Table, room temperature)

Velocity light in a vacuum

= 3 x 10⁸ m/s
(Reference Table)

Wikimedia
Intracloud lightnings over Toulouse (France).
Original source is Image:Lightnings sequence 2.jpg,

About how many times faster is light
than sound?

Reference Table

About 1 million times

Gap between time you see lightning and time you hear thunder tells ....

... distance of lightning

If time gap is small?

Lightning is close

Large gap of time?

Lightning far away

Did you know ...

'...you can approximate the storm's distance in miles by counting the seconds between the lightning and thunder and dividing by five. It takes about five seconds for the sonic boom to travel one mile, so if you see the sky illuminated by a streak of lightning and count 10 seconds until you hear the low rumble of the thunder, the storm is about two miles away.'

- Ask Yahoo

Vibrating Tuning Fork - Slow Motion

Wavelength, frequency, period, speed, amplitude.

Which 3 are determined by the source of a wave?

Summary
Source	Medium
frequency	speed
period	wavelength
amplitude

Doppler Effect