Unit of Wavelength - Definition, SI Unit, FAQs

What is Wavelength?

Wavelength is the length of one complete wave cycle.

• In transverse waves, it is the distance between two crests or two troughs.
• In longitudinal waves, it is the distance between two compressions or two rarefactions.

Wavelength determines the colour of light, pitch of sound, and properties of electromagnetic waves.

What is the Unit of Wavelength?

SI Unit of Wavelength: Metre (m)
Since wavelength is a length, its SI unit is the same as that of any length:

$\text { Wavelength unit }=\text { metre }(\mathbf{m}) $

Symbol for Wavelength:
The symbol for wavelength is: $\lambda$

Dimensional Formula of Wavelength: $\left[M^0 L^1 T^0\right]$

Why Do We Use Different Units for Wavelength?

Wavelengths can be extremely long (radio waves) or extremely short (X-rays), so smaller or larger metric units are used depending on the wave type.

All Units of Wavelength

Wavelength Units Used in Different Waves

Relationship Between Wavelength and Frequency

The wavelength of a wave is related to its speed and frequency by:

$\lambda=\frac{v}{f}$
For light in vacuum:

$\lambda=\frac{c}{f}$
Where:

• $\lambda=$ wavelength
• $v$ or $c=$ speed of wave
• $f=$ frequency

Example Problem - How to Calculate Wavelength

Question: Find the wavelength of radiation whose frequency is $5 \times 10^{14} \mathrm{~Hz}$.
Solution:

$\lambda=\frac{c}{f}=\frac{3 \times 10^8}{5 \times 10^{14}}=6 \times 10^{-7} \mathrm{~m}$

or

$600 \mathrm{~nm}$
Summary

• Wavelength measures the length of one wave cycle.
• Symbol: $\lambda$
• SI Unit: metre (m)
• Smaller units: $\mathrm{nm}, \mu \mathrm{m}, \mathrm{pm}$
• Bigger units: $\mathrm{km}, \mathrm{Mm}$
• Shorter wavelength $\rightarrow$ higher frequency and energy
• EM waves have wavelengths from $10^{-12} \mathrm{~m}$ to $10^3 \mathrm{~m}$

Also check-

• NCERT Exemplar Class 11th Physics Solutions
• NCERT Exemplar Class 12th Physics Solutions
• NCERT Exemplar Solutions for All Subjects

NCERT Physics Notes:

• NCERT Notes Class 11th Physics
• NCERT Notes Class 12th Physics
• NCERT Notes For All Subjects