Law of Refraction Explained

Refraction refers to the way light changes speed and direction as it travels across the interface between one transparent medium to another.

Refractive index (index of refraction) determines how much slower light travels through a given medium than through a vacuum.

When light crosses a boundary into a medium with a high refractive index (eg. diamond = 2.42) there is a significant change in direction and speed. When light crosses a boundary into a medium with a low refractive index (eg. water = 1.333) there is a less significant change in direction or speed.

Yes! When light leaves a vacuum or travels from one transparent medium into another, it undergoes refraction causing it to change both direction and speed.

As light travels from a fast medium such as air to a slow medium such as water it bends toward 'the normal' and slows down. As light passes from a slow medium such as diamond to a faster medium such as glass it bends away from 'the normal' and speeds up.

A nanometre (nm) is a unit of length in the metric system, equal to one billionth of a metre (1 nm = 1 × 10⁻⁹ metres). It is commonly used to measure extremely small distances, particularly at the atomic and molecular scale.

• In the context of light and electromagnetic radiation, a nanometre is often used to describe wavelengths of visible light.
  The wavelength of visible light ranges from about 700 nm (red) to 400 nm (violet).
• Nanometres are also used to measure components like the thickness of materials, the size of particles in nanotechnology, and the spacing between atoms in a crystal lattice.

In physics and optics, a medium refers to any material through which light or other electromagnetic waves can travel. It’s essentially a substance that acts as a carrier for these waves.

• Light is a form of electromagnetic radiation, which travels in the form of waves. These waves consist of oscillating electric and magnetic fields.
• The properties of the medium, such as its density and composition, influence how light propagates through it.
• Different mediums can affect the speed, direction, and behaviour of light waves. For instance, light travels slower in water compared to a vacuum.
• Examples of Mediums:
  • Transparent: Materials like air, glass, and water allow most light to pass through, with minimal absorption or scattering. These are good examples of mediums for light propagation.
  • Translucent: Some materials, like frosted glass or thin paper, partially transmit light. They allow some light to pass through while diffusing or scattering the rest.
  • Opaque: Materials like wood or metal block light completely. They don’t allow any light to travel through them.

In mathematics, the sine is a trigonometric function of an angle.

• The sine of an acute angle is defined in the context of a right-angle triangle.
• For any specified angle, it’s sine is the ratio of the length of the side opposite that angle, to the length of the longest side of the triangle (the hypotenuse).
• The mathematical notation for sine is sin.

Wavelength measures a complete wave cycle, which is the distance from any point on a wave to the corresponding point on the next wave.

• While wavelength can be measured from any point on a wave, it is often simplest to measure from the peak of one wave to the peak of the next or from the bottom of one trough to the bottom of the next, ensuring the measurement covers the whole of the cycle.
• The wavelength of an electromagnetic wave is usually given in metres.
• The wavelength of visible light is typically measured in nanometres, with 1,000,000,000 nanometres making up a metre.
• Radio waves, visible light, and gamma waves for example, each have different ranges of wavelengths within the electromagnetic spectrum.

The angle of incidence measures the angle at which incoming light strikes a surface.

• The angle of incidence is measured between a ray of incoming light and an imaginary line called the normal.
• See this diagram for an explanation: Reflection of a ray of light
• In optics, the normal is a line drawn on a ray diagram perpendicular to, so at a right angle to (90⁰), the boundary between two media.
• If the boundary between the media is curved, then the normal is drawn at a tangent to the boundary.

In the field of optics, diffusion refers to situations that cause parallel rays of light to spread out more widely.  When light undergoes diffusion it becomes less concentrated. Diffuse reflections occur when light scatters off rough or irregular surfaces.

• When microscopic features on a surface are significantly larger than the individual wavelengths of light within the visible spectrum, each wavelength of light encounters bumps and ridges exceeding their size.
• Instead of reflecting neatly in one direction, the light scatters in different directions.
• In this case, scattering doesn’t happen completely randomly. The surface features influence the direction of the scattered light, depending on the angle of incidence and the specific bumps and ridges it encounters.
• This scattering creates diffuse reflections, responsible for the soft, uniform illumination seen on textured surfaces like matte paint or unpolished wood.
• In the case of a matte phone screen, for example, the light doesn’t form a clear reflection of your face but rather creates a soft, hazy glow due to the diffused light.

The angle of refraction measures the angle to which light bends as it passes across the boundary between different media.

• The angle of refraction is measured between a ray of light and an imaginary line called the normal.
• In optics, the normal is a line drawn on a ray diagram perpendicular to, so at a right angle to (90⁰), the boundary between two media.
• See this diagram for an explanation: Refraction of a ray of light
• If the boundary between the media is curved, the normal is drawn perpendicular to the boundary.

Optical density is a measure of how much a material resists and slows the transmission of light.

• The higher the optical density of a material, the slower light travels through it.
• The lower the optical density of a material, the faster light travels through it.
• A vacuum is not a medium and has zero optical density.
• Light travels through a vacuum at the maximum possible speed of light which is 299,792 kilometres per second.
• Optical density and refractive index are related properties.
• In general, materials with higher optical density tend to have higher refractive indices and vice versa.
• The greater the difference in refractive index between two materials, the more they will bend light when they come into contact.