Properties of Wave Pulses and Waves
Waves transfer energy through a disturbance without carrying the medium as a whole with them. Mechanical waves require a medium, electromagnetic waves do not, transverse disturbances are perpendicular to propagation, longitudinal disturbances are parallel, and the medium helps determine wave speed.
Properties of Wave Pulses and Waves: quick answer
Waves transfer energy through a disturbance without carrying the medium as a whole with them. Mechanical waves require a medium, electromagnetic waves do not, transverse disturbances are perpendicular to propagation, longitudinal disturbances are parallel, and the medium helps determine wave speed. The key distinction is between the traveling pattern and the local motion of the medium. Following one piece of string or one air parcel prevents the common mistake of imagining that matter is carried with the wave.
Keep superposition and standing-wave calculations in Topic 14.6. For Topic 14.1, focus on energy transfer, medium dependence, transverse/longitudinal structure, amplitude, and the physical factors that set wave speed.
What you should be able to explain and do
Use these as closed-note retrieval prompts before opening the worked reasoning.
Distinguish a wave pulse from a continuous/repeating wave and explain energy transfer without net matter transport.
Classify transverse and longitudinal disturbances from the direction of local motion relative to propagation.
Compare mechanical and electromagnetic waves by whether a material medium is required.
Use string tension and linear mass density to predict or calculate wave-speed changes.
Key terms for this wave model
Definitions stay next to the model so no important term requires leaving the lesson to understand the explanation.
wave pulse
wave pulse is a single disturbance that travels through a medium or field.
wave
wave is a disturbance that transfers energy from one region to another without net transport of the medium as a whole.
mechanical wave
mechanical wave is a wave that requires matter to provide the restoring interaction and inertia needed for propagation.
electromagnetic wave
electromagnetic wave is an oscillating electric-and-magnetic-field disturbance that can propagate through vacuum.
transverse wave
transverse wave is a wave whose disturbance is perpendicular to the direction of propagation.
longitudinal wave
longitudinal wave is a wave whose disturbance is parallel to the direction of propagation.
compression and rarefaction
compression and rarefaction is regions of increased and decreased density/pressure in a longitudinal wave such as sound.
amplitude
amplitude is the maximum magnitude of the disturbance from equilibrium; larger amplitude corresponds to greater transported energy for otherwise comparable waves.
Match every relationship to its conditions
Some Unit 14 relationships are intentionally qualitative. Keep the variable meanings, geometry, and scope attached to each statement.
| Relationship / model | Variables & units / meaning | When to use it | Physical anchor |
|---|---|---|---|
v_string = √(F_T/μ) | v_string wave speed on an ideal string (m/s); F_T tension (N); μ linear mass density (kg/m) | a transverse wave on a stretched uniform string | increasing tension raises wave speed; increasing linear density lowers it |
μ = m/ℓ | μ linear mass density (kg/m); m string mass (kg); ℓ string length (m) | converting a uniform string mass and length into the property that controls string-wave speed | a 0.020 kg string 2.0 m long has μ=0.010 kg/m |
greater amplitude → greater transported energy | qualitative model statement; compare otherwise similar waves in the same medium | comparing how much energy similar wave disturbances carry | a larger-amplitude sound wave is associated with greater intensity/loudness than an otherwise similar smaller-amplitude wave |
What the diagram or graph must show
Translate physical situation ↔ diagram/graph ↔ relationship ↔ verbal prediction.
Pulse snapshot
mark propagation direction separately from the local displacement direction.
Longitudinal sketch
label compression, rarefaction, and particle-motion direction.
Speed comparison
increase tension or linear density one at a time and predict the change before calculating.
Amplitude evidence
compare otherwise similar waves and connect larger amplitude with greater transported energy.
Change one wave condition and inspect what responds
Predict first, then move one control. The tool is constrained to the topic model rather than introducing extra equations.
Two examples with model selection exposed
Each example identifies the representation/condition before the arithmetic or qualitative conclusion.
String-speed comparison
Situation: Two identical strings have the same μ, but string B has four times the tension of string A.
Reasoning: Because v∝√F_T at fixed μ, the speed ratio is √4=2.
String B carries pulses at twice the speed.
Linear density
Situation: A uniform 0.030 kg string is 3.0 m long and held at 9.0 N tension.
Reasoning: μ=m/ℓ=0.010 kg/m, then v=√(9.0/0.010).
v=30 m/s.
Recognize the physics before reaching for an equation
Use the cue to choose the model, connect it to nearby ideas, then reject any method whose assumptions do not match the situation.
What should trigger Topic 14.1?
Use the wave-pulse model when disturbances propagate and the task asks about transverse/longitudinal character, superposition, or energy transfer without bulk matter transport.
How this idea fits the course
This foundational wave language supports periodic-wave quantities in 14.2 and all later interference/diffraction topics.
Scope check before solving
Keep superposition and standing-wave calculations in Topic 14.6. For Topic 14.1, focus on energy transfer, medium dependence, transverse/longitudinal structure, amplitude, and the physical factors that set wave speed.
Turn the model into measurable evidence
Plan what changes, what is measured, which representation tests the model, and what uncertainty would weaken the conclusion.
Investigation target
Launch pulses along strings with different tensions or linear densities, measure travel time over a fixed distance, and test how the observed speed changes with the string properties.
Reasoning errors to eliminate
Repair the representation or scope decision before doing more arithmetic.
Six things to do before moving on
Use these as closed-note transfer prompts.
- I can identify the relevant wave representation before choosing an equation.
- I can define every wavelength, frequency, period, angle, aperture/slit spacing, index, or film thickness I use.
- I can predict the qualitative trend before calculating a numerical result.
- I can state when a relationship is qualitative-only or relies on a small-angle/normal-incidence assumption.
- I can translate between physical pattern, diagram/graph, equation/model statement, and verbal claim.
- I can design or critique a wave experiment and justify a conclusion from data and uncertainty.
Practice is kept on its dedicated pages
Finish the lesson first. Then open the separate topic bank when you want exam-style practice without replacing the teaching content above.
42 multiple-choice questions
Use the exact-topic MCQ bank to test model selection, representations, calculations and boundaries after learning the concept.
Open 42 Topic MCQs4 multipart free-response tasks
Use the exact-topic FRQ set for mathematical, representation, experimental and qualitative/quantitative reasoning.
Open 4 Topic FRQsTopic 14.1 FAQs
Does the material travel with the wave?
No. The medium generally oscillates locally while the disturbance transfers energy.
What makes a wave mechanical?
It needs a material medium for the disturbance to propagate.
Is light mechanical?
No. Electromagnetic waves can propagate through vacuum.
What raises string-wave speed?
Greater tension raises speed; greater linear mass density lowers it.
How does amplitude relate to energy?
For otherwise comparable waves, greater amplitude means greater transported energy.