LIGHT & THE ELECTROMAGNETIC SPECTRUM

What is WHITE LIGHT made of? LIGHT AND COLOUR What is WHITE LIGHT made of? Lab on White Light

LIGHT AND COLOUR White Light Light that appears white to the eye, composed of some combination of light with frequencies in the red, blue, and green parts of the spectrum

ENERGY IN A WAVE Wave Is a disturbance that transfers energy from one point to another without transferring matter. In a water wave, energy passes through the water from one point to another as the wave rises and falls. This energy allows the wave to do work. Play Surfing Video

ENERGY IN A WAVE Wave Imagine that a duck sits on the surface of a lake. The duck moves up and down with the wave, which means that the wave transfers energy to the duck.

ENERGY IN A WAVE Wave The water moves up and down, but the water does not move forward with the wave. Only energy moves forward. Water and the duck move up and down with each wave. Energy moves forward.

ENERGY IN A WAVE Properties of Waves (how waves transfer energy) Highest point of the wave is called a crest. Lowest point of a wave is called a trough. The level of the water when there are no waves is called the rest position.

ENERGY IN A WAVE Properties of Waves (how waves transfer energy) Amplitude Wavelength Rest Position

ENERGY IN A WAVE Properties of Waves (how waves transfer energy) Wavelength The distance from crest to crest. Standard symbol for wavelength is . Wavelength is measured in meters.

ENERGY IN A WAVE Properties of Waves (how waves transfer energy) Amplitude Wave height (from the rest position of the wave to the crest or the wave depth from the rest position to the trough. The energy transferred by a wave depends, in part, on it amplitude.

ENERGY IN A WAVE Properties of Waves (how waves transfer energy) Amplitude Wavelength Rest Position

ENERGY IN A WAVE Properties of Waves (how waves transfer energy) Amplitude The larger the amplitude, the more energy that is carried. The smaller the amplitude, the less energy that is carried.

ENERGY IN A WAVE Properties of Waves (how waves transfer energy) Frequency The rate of repetition of a wave. For example, if wave crests pass the dock 10 times in a minute, the frequency of the wave is 10 cycles per minute. Quick Activity page 383 Begin tapping the surface of the water. This will create a series of wave crests. Suppose you made on new wave crest every second. Would it take more energy or less energy to create three wave crests every second? It would take more energy because you would need to tap much faster. When you create more wave crests per second, the frequency increases, the crests are closer together. So, as more energy is put into making a wave, the frequency of the wave increases and the wavelength shortens. Frequency Increases – Wavelength Decreases Frequency Decreases – Wavelength Increases

ENERGY IN A WAVE Properties of Waves (how waves transfer energy) Frequency The higher the frequency, the more energy the wave passes along. The standard symbol for frequency is f. It is measured in hertz (Hz), which is cycles per second.

ENERGY IN A WAVE Properties of Waves (how waves transfer energy) Amplitude Wavelength Rest Position

ENERGY IN A WAVE Mathematical relationship among the speed v, the frequency f, and the wavelength . v = f x  For example, if the wavelength of a wave is 5cm and the frequency is 10 cycles/s, then the speed is v = 10 x 5 = 50 cm/s Have the students complete an activity that requires them to draw and label a wave including crest, trough, rest position, wavelength and amplitude. Have them also answer questions on finding speed etc.

THE ELECTROMAGNETIC SPECTRUM Light is a form of energy. Visible light is only a tiny fraction of the energy that surrounds us every day. We are also surrounded by invisible light- like waves, which together with visible light are called electromagnetic radiation.

THE ELECTROMAGNETIC SPECTRUM Electromagnetic radiation is a wave pattern made of electric and magnetic fields that can travel through empty space. The entire range of electromagnetic radiation extends from the shortest gamma rays to the longest radio waves and includes light. This range is called electromagnetic spectrum.

The Electromagnetic Spectrum Low energy High energy Radiowaves Microwaves Infrared . Ultra-violet X-Rays GammaRays Low Frequency High Frequency Long Wavelength Short Wavelength Watch Video. Have the students open their text book to page 384-385. In groups assign the students on of the uses of the Electromagnetic Spectrum. They will highlight the main points on a large piece of paper and draw an example of it. They will then present to the class. Provide the students with a handout to fill in during the presentations. Visible Light

THE WAVE MODEL OF LIGHT This model is used to show similarities between light and the movement of waves on the surface of water to explain several properties of light that we can see. When light is shone through a prism the light separates into the colours of the rainbow – red, orange, yellow, green, blue and violet. Show an example of light shone through a prism

Prism White light is made up of all the colors of the visible spectrum. Passing it through a prism separates it.

If the light is not white Passing this light through a prism does something different.

Additive Colour Theory of Light White light is composed of different colours (wavelengths) of light. All three primary colours together produce white light. When paired they can create magenta, yellow and cyan. Colour Lab – extraction of chlorophyll

SUBTRACTIVE COLOUR THEORY OF LIGHT When a light wave strikes an object, some wavelengths of light reflect. Others are absorbed. The colours that are absorbed are subtracted from the reflected light that is seen by the eye. Need a lab