Clil 4A L.Scientifico – 2° Lesson

Lesson 2: The Second physics lesson with a native speaker of English
The topic is “Diffraction of light”

Keywords:
  • Light properties
  • To pass through
  • An angle
  • A beam/ray of light
  • Spectrum of colours
  • Moist in the air
  • Density
  • “Richard of York gave battle in vain”
  • Indigo
  • Interference of light
  • Mixture of colours
  • Diffraction of light
  • A slit – it is a narrow opening in a barrier
  • To bend
  • Bands of light
  • Constructively
  • Destructively
  • Coherent
  • A fringe

Light is a wave. Light travels through the vacuum of space from the Sun to the Earth in a form of a line. This line is called a ray or a beam of light. Light travels very quickly. There is nothing that can travel faster.

One of the properties of light is that it can pass through transparent materials (water, air, glass). Light travels at different speeds in different materials because they have different densities. The higher the density, the slower light travels. Light can enter these materials at different angles. Depending on the angle, light can bend. How much the light bends depends on its colour.

Colours of light: The seven colours of light are: Red, Orange, Yellow, Green,  Blue, Indigo and Violet. You can remember the colours and order with the help of this phrase:  “Richard of York gave battle in vain”.

The different colours of light have each a different frequency and wavelength. Red light has the longest wavelength and violet light has the shortest wavelength.

How can you see the colours of light? The division of light into its component parts produces a spectrum. You can use a prism for that. A prism will divide white light into different colours. In nature the spectrum of light is a rainbow that you can see in the sky. It happens because the moist (water) that is contained in the air after raining can also divide light into colours.

Refraction: bending of light when it passes through transparent materials like glass or water.

Reflection: is the change in direction of a light wave between two different media so the light wave returns to the medium from which it originated.

Diffraction is bending of light around the corners of an object. When an object is not transparent, light cannot pass though it, so it will avoid the obstacle.

Interference: it is when two or more rays of light interact with each other. There are two types of interference: constructive and destructive. We can refer to the Thomas Young’s experiment to understand it better.

                                 Thomas Young’s double slit experiment

Thomas Young observed this phenomenon: when two portions of light coming from the same source combine together, they produce dark and light bands. Light bands are produced when the light portions combine constructively because they are coherent. And dark bands are produced when the light portions combine destructively. It depends on the angles at which two rays of light interact. The line of dark and bright bands is called a fringe.

For this experiment he used: two barriers with slits (small openings), one source of light and a screen.

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Special Thanks to Olena Shlap (native speaker of English)