EQ2) Can you use the scientific method to explain what light is?
Reference CS5 pg 122 - 131
What is Light???
Light is so common that we rarely think about what it really is. But just over two hundred years ago, a groundbreaking experiment answered the question that had occupied physicists for centuries. Is light made up of waves or particles? The experiment was conducted by Thomas Young and is known as Young's Double Slit Experiment. This famous experiment is actually a simplification of a series of experiments on light conducted by Young. In a completely darkened room, Young allowed a thin beam of sunlight to pass through an aperture on his window and onto two narrow, closely spaced openings (the double slit). This sunlight then cast a shadow onto the wall behind the apparatus. Young found that the light diffracted as it passed through the slits, and then interfered with itself, created a series of light and dark spots. Since the sunlight consists of all colours of the rainbow, these colours were also visible in the projected spots. Young concluded that light consist of waves and not particles since only waves were known to diffract and interfere in exactly the manner that light did in his experiment. However, other scientists including Einstein were conducting experiment in which light is clearly acting like a photon. Hence Is light a wave or a particle? What makes evidence reliable and valid? |
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1.8) The Wave Model
a) Read from page 122 up to the investigation 4.3)
b) Use the powerpoint to answer the questions on the worksheet provided. |
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A) Absorption and Colour
A substance is transparent when all or most of the light passes through and we can see objects on the other side clearly
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A substance is Translucent when the surface of the material is rough and light passes through but is scattered. Hence we cannot see objects on the other side clearly
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A substance is opaque when no light travels through them and is instead reflected or absorbed
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1.9) Maxwell, Young and The Electromagnetic Spectrum
Maxwell and Young were two scientists who proved to the world that light is a wave. Maxwell developed a mathematical theory for light. His mathematics showed that light would have very important properties such as reflection, refraction, speed etc which were measured many times to be true. Young provided a famous experiment that proved light is a wave. Their evidence was strong, reliable and valid
Maxwell and Young were two scientists who proved to the world that light is a wave. Maxwell developed a mathematical theory for light. His mathematics showed that light would have very important properties such as reflection, refraction, speed etc which were measured many times to be true. Young provided a famous experiment that proved light is a wave. Their evidence was strong, reliable and valid
Visible light is actually made of an electric field and a magnetic field moving together and hence visible light is actually an electromagnetic wave.
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There are many different other types of electromagnetic waves -
a) Gamma rays b) x-rays c) Ultraviolet radiation d) visible light e) infrared radiation f) Microwaves g) Radio and TV waves Our lives would be very different if we could not use these electromagnetic waves. They are very important to us and the many different technologies that we rely on. |
Task 1) The Many Different Uses of Electromagnetic Waves
Complete the table provided to gain an insight into some of the many different ways that we rely on electromagnetic waves
Complete the table provided to gain an insight into some of the many different ways that we rely on electromagnetic waves
Task 2) Light is a Wave!
Maxwell devised a mathematical model of light that showed that if it is a wave then it would have the following properties:
a) Reflection b) Refraction c) Polarisation d) Interference Then Young proved that all types of light have these properties and his most famous experiment was known as "Young's Double Slit Experiment" as it showed that light can be split into two waves by a double slit and that these two waves will interfere and produce an interference pattern of light and dark bands as shown below. |
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The result of Young's experiment was a pattern of light and dark bands. Every scientist was convinced that light was a wave.
Task 3) Light is a Particle
Planck, then, put a spanner in the works. He proposed that light actually consisted of particles of energy called photons. Each colour of light consists of photons that have different energies. Red photons have a smaller amount of energy than blue light
Einstein, then, conducted an experiment called "The Photoelectric Effect" and proved that light must consist of photons. We are going to make a model of this experiment!!!! |
Einstein eventually proved that in some experiments light is a wave and in other experiments light is a particle and hence it must be both - the Wave/Particle Duality of Light!!!!!