Recall that visible light of a single frequency is described as monochromatic

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Cambridge IGCSE Physics - Thin Lenses - Monochromatic Light

Thin Lenses

3.2.3 Thin Lenses

This section focuses on the properties of thin lenses, particularly the concept of monochromatic light.

Monochromatic Light

Visible light is a form of electromagnetic radiation that spans a range of wavelengths, each corresponding to a different colour. However, when we talk about light in the context of lens calculations, we often consider light of a single frequency (or wavelength). This is described as monochromatic light.

  • Monochromatic means consisting of or relating to a single wavelength of light.
  • Examples of monochromatic light sources include lasers and light from incandescent bulbs filtered to isolate a specific colour.
  • Using monochromatic light simplifies lens calculations as we only need to consider the lens's focal length and the geometry of the light rays.

Why is Monochromatic Light Important?

The calculations for thin lenses are simplified when using monochromatic light. The refractive index of the lens material is constant for a given wavelength of light. Therefore, we don't need to consider dispersion (the separation of white light into its constituent colours) in our lens equations.

Key Concept: Wavelength and Frequency

Light is characterised by its wavelength ($\lambda$) and frequency ($f$). These are related by the speed of light ($c$):

$$c = \lambda f$$

Where:

  • $c$ is the speed of light in a vacuum (approximately $3.0 \times 10^8 \, m/s$).
  • $\lambda$ is the wavelength of the light.
  • $f$ is the frequency of the light.

Monochromatic light has a single, well-defined wavelength.

Table: Summary of Monochromatic Light

Property Description
Definition Light consisting of a single wavelength.
Importance in Lens Calculations Simplifies calculations by eliminating the need to consider dispersion.
Example Sources Lasers, filtered light from incandescent bulbs.
Relationship to Frequency Monochromatic light has a single, well-defined frequency.

Understanding the concept of monochromatic light is crucial for correctly applying the lens equations and solving problems involving thin lenses.