C
CraftExam
medium difficulty7 min

Wave Characteristics

Wave characteristics are measurable features of a wave, mainly wavelength, frequency, time period, and amplitude.

In one line: Frequency counts how often; time period tells how long for one.

Practice This Concept

Understand it

  • Wavelength is the distance between two consecutive compressions or two consecutive rarefactions.
  • Frequency is the number of vibrations per second, measured in hertz.
  • Time period is the time for one complete vibration.
  • Amplitude is the maximum displacement from the mean position and is linked with loudness.

Example

If a tuning fork vibrates 256 times in one second, its frequency is 256 Hz and its time period is 1/256 s.

Rule to remember

Frequency f = number of vibrations/time; time period T = 1/f; wavelength λ is distance between consecutive compressions or rarefactions.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

A source completes 240 vibrations in 3 s.

  1. 1Frequency = 240/3 = 80 Hz.
  2. 2Time period = 1/80 s = 0.0125 s.

Method you can reuse

  1. 1List given quantity.
  2. 2Use f = vibrations/time for frequency.
  3. 3Use T = 1/f for time period.
  4. 4Write correct units in the final answer.

Sketch it in your answer

Label compression, rarefaction, wavelength, and amplitude on a wave representation. Show wavelength between two consecutive compressions.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

If a sound source completes 100 vibrations in 2 seconds, what is its frequency?

Think first, then show answer
Its frequency is 50 Hz because frequency equals number of vibrations divided by time, so 100 divided by 2 is 50 vibrations per second.

Common wrong answer

Frequency is 240 Hz for 240 vibrations in 3 s.

Why it loses marks: The vibrations must be divided by time.

Don't mix this up

Students often confuse frequency with amplitude. Frequency affects pitch, while amplitude affects loudness.

Exam tip

Write units carefully: wavelength in metre, frequency in hertz, time period in second, and amplitude in metre.

Wave Characteristics diagram

Open full screen to read every label clearly.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Questions may ask definitions with units, identification from a graph, or simple calculation of frequency and time period.
  1. 1

    Enough for 1 mark

    Wave characteristics are measurable features of a wave, mainly wavelength, frequency, time period, and amplitude.

  2. 2

    Add for 2 marks

    Example: If a tuning fork vibrates 256 times in one second, its frequency is 256 Hz and its time period is 1/256 s.

  3. 3

    Add for 3 marks

    Wavelength is the distance between two consecutive compressions or two consecutive rarefactions.

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