Transverse and longitudinal waves IB DP Physics Study Notes - 2025 Syllabus

Transverse and longitudinal waves IB DP Physics Study Notes

Transverse and longitudinal waves IB DP Physics Study Notes at IITian Academy focus on specific topic and type of questions asked in actual exam. Study Notes focus on IB Physics syllabus with Students should understand

the nature of sound waves
wavelength (\(\lambda\)), frequency (\(f\)), time period (\(T\)), and wave speed (\(v\)) in wave motion is given by:
\(v = f\lambda = \frac{\lambda}{T}\)

Standard level and higher level: 3 hours
Additional higher level: 4 hours

IB DP Physics 2025 -Study Notes -All Topics

The nature of sound waves

A “microscopic” view of a sound pulse may help:

FYI

As you watch, observe that…
there is a pulse velocity v.
there is a compression or condensation.
there is a decompression or rarefaction.
the particles are displaced parallel to v.

Wavefronts and rays

Looking at a snapshot of the previous 2D animation we can label various parts:
The wavefronts are located at the compressions.
The rays are drawn from the source outward, and show the direction of the wave speed or velocity.

FYI

Rays and wavefronts are perpendicular to each other.

Crests and troughs

Compare the waves traveling through the mediums of rope and spring.

Explaining the motion of particles of a medium

Here is an animation of transverse wave motion created by placing each of the blue particles of the medium in simple harmonic motion.
As you watch the animation note that
each particle has the same period T.
each particle is slightly out of phase.
the wave crest appears to be moving left.
Consider a snapshot of the following identical mass/spring systems, each of which is oscillating at the same period as the system to the right.
Note that they are all out of phase in such a way that they form a wave as you move in the x-direction.
At each position x we have a different value y.
The systems at x1 and x2 are ¼ cycle out of phase.
Now we see the same system a short time later:
The mass at x1 has gone lower.
The mass at x2 has gone lower.
Which way does it appear the wave is traveling?
Left or right?

Displacement and amplitude

If we look at either of the graphs we can define various wave characteristics:
The signed distance from the equilibrium position is called the displacement. In this graph it would be the y value.
At a horizontal coordinate of x₁ along the length of the wave train we see that its displacement y is (-), whereas at x₂ we see that y is (+).
The amplitude is the maximum displacement. The amplitude is just the distance from crest to the equilibrium position.

Period and wavelength

The length in the horizontal dimension over which a wave repeats itself is called the wavelength, represented with the symbol λ (the Greek lambda).
The wavelength λ is the distance from crest to crest (or trough to trough).
The period T is the time it takes a wave crest to travel exactly one wavelength.

FYI
The period is the same for all particles of the medium.

Wave Speed and Frequency

The speed at which a crest is moving is called the **wave speed**. This is a measure of the rate at which a disturbance travels through a medium.
Since the time it takes a crest to move one complete wavelength (\(\lambda\)) is one period (\(T\)), the relation between \(v\), \(\lambda\), and \(T\) is:
Finally, **frequency** (\(f\)) measures how many wave crests per second pass a given point. It is measured in cycles per second or Hz. Again, \(f = \frac{1}{T}\).

PRACTICE:

A spring is moved in SHM by the hand as shown. The hand moves through 1.0 complete cycle in 0.25 s. A metric ruler is placed beside the waveform.

(a) What is the wavelength?

(b) What is the period?

Solution:

(a)λ = 4.7 cm = 0.047 m.

(b)T = 0.25 s.

Transverse and longitudinal waves IB DP Physics Study Notes

Transverse and longitudinal waves IB DP Physics Study Notes - 2025 Syllabus