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What is Light?

What is Light?. Optics Unit. So ... What is light?. Think – Pair – Share!. What is Light?. Greeks  Pythagoras: a stream of particles emitted from a source of light. (6 th century BC ) This makes sense. Light from the sun makes us feel warm, it’s a form of energy.

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What is Light?

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  1. What is Light? Optics Unit

  2. So ... What is light? • Think – Pair – Share!

  3. What is Light? • Greeks  Pythagoras: a stream of particles emitted from a source of light. (6th century BC) • This makes sense. Light from the sun makes us feel warm, it’s a form of energy. • How do you transfer energy? You move it...electricity is flow of electrons; heat a frying pan by making its atoms collide together.

  4. What is Light? • Light travels a great distance in a straight line, and bounces off a mirror much like a ball bouncing off a wall. • But we can’t see this light particle. Too small? Too fast? • Aristotle: light moved as a wave, ripples in water (4 BC) • Waves are travelling energy. Your hand in a tub of water creates waves. • Observe light passing through narrow opening, it can spread out…or interfere with light passing through a second opening. Similar to how ripples in water behave. Not something that particles would do. • But waves must travel through some medium…space is empty

  5. What is Light? • Centuries pass, arguments ensue. • Particle - Newton • Wave – Christian Huygens • Particle • Wave • 20th century, both theories have some validity • Einstein – stream of energy packets called photons

  6. What is Light? • A stream of photons that are massless particles each travelling with wavelike properties at the speed of light. • A photon is the smallest quantity of energy which can be transported.

  7. Properties of Light • Light travels in straight lines (rectilinear propagation) • Light does not need a medium to travel (it travels in vacuum - empty space with no matter) ...... unlike sound which requires a medium • In vacuum or air, speed of light is constant (c = 3.0 x 108 m/s) • It turns out that visible light is just a small part of a spectrum called Electromagnetic Radiation

  8. Rectilinear Propagation • Light travels in a straight line as long as it is travelling through the same medium. • We see proof of this everyday. • We only need to look at the crisp outlines of a shadow on a bright sunny day.  • We refer to a ray as being the path taken by light energy. • A beam of light is a stream of light rays.

  9. Electomagnetic Spectrum • The range of electromagnetic waves (from low to high energy)

  10. Visible Light: • Electromagnetic waves that the human eye can see • Ex. red light • Invisible Light: • Electromagnetic waves that the human eye cannot see • Can still detect them and use them for many things • Ex. radio waves

  11. Visible Light Spectrum • White light is made up of: Red, orange, yellow, green, blue, indigo and violet(ROY G BIV)

  12. Visible Light experiment • Complete the ‘Try This’ activity on pg 467

  13. How does this work? • A triangular prism slows down the speed of light • Each colour is slowed differently because of differing energy levels- this separates white light into different colours!

  14. Electromagnetic Waves in our Society • Use the chart on pg466 to complete your worksheet

  15. Homework • Pg. 469 #3, 4, 5, 9, 11

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