3.2 Models used to explain the properties of electromagnetic radiation Name:_____________________ Date:______________________ Block:______

Models explain the properties of electromagnetic radiation? Scientists use models to represent ideas and concepts. Visible light is often used as a model to study other types of electromagnetic radiation Properties of electromagnetic radiation: Invisible as it travels Involves the transfer of energy from one place to another Can travel through empty space Travels through empty space at the speed of light: 3.00 x 108 m/s Has both electrical and magnetic properties physical property:

Visible light can be used to model all types of electromagnetic radiation. The seven types of electromagnetic radiation have a lot in common. Studying one type can tell you a lot about the others Visible light is used as a model to study electromagnetic radiation Easy and safe to study Becomes visible when it interacts with matter

Ray Model of Light Greek mathematician Euclid suggested that light travels in straight lines This led to the development of the ray model of light The ray model of light suggest that light travels in straight lines called rays A ray is an arrow that is used to show the direction of the straight-line path of light ray model of light: the idea that light travels in straight lines

Ray Model of Light The ray model of light will produce ray diagrams Used to study and predict how light behaves Rays can be used to predict the location, size, and shape of shadows A shadow is the darker area behind an object, created when the object blocks the light rays from a light source that is in front of the object.

Ray Diagrams and Shadows Do you notice that the distance between an object and the light source affects the size of the shadow. What happens to the shadow when the object in front is close to the light source? What happens to the shadow when the object in front is far from the light source?

Ray Diagrams to Model Visible Light Light rays spread out as they travel from a light source and get dimmer with distance.

The wave model of light explains that light has wave-like properties. Some scientists describe light as a stream of particles called photons Photons have particle-like properties The Particle Model of Light is used to describe light as fast moving particles Sir Isaac Newton was one of the first scientist to propose that light has these properties. However, he could not demonstrate this in an experiment. In the early 1800’s, Thomas Young performed an experiment that supported the idea that light has properties of a wave Wave model of light: the idea that light has wave-like properties particle model of light: the idea that light has particle-like properties wave model of light: the idea that light has wave-like properties

Types of waves found in nature Transverse waves Light, heat and water are made up of transverse waves Motion of wave is perpendicular to the direction of energy transfer

Types of waves found in nature Compression waves Sound waves and seismic waves are made up of compression waves motion of wave is parallel to the direction of energy transfer

Properties of Light Waves Light waves have some things in common with water waves Both move energy from one place to another Both have wavelength, amplitude, and frequency .

Properties of Light Waves Crest Centre line Trough Crest: highest point of a wave Trough: lowest point of a wave Amplitude: distance from the centre line to the crest OR distance from the centre line to the trough distance from the centre line to the crest = distance from the centre line to the trough

Properties of Light Waves Wavelength wavelength: the distance from one crest (or trough) of a wave to the next crest (or trough) amplitude: the distance from the centre line to the crest of trough of the wave Wavelength Wavelength: distance from one crest to the next crest OR distance from one trough to the next trough or centre line to centre line (with a crest and trough in between)

Properties of Light Waves Short wavelengths mean higher energy Long wavelengths mean less energy

Properties of Light Waves Frequency: the number of complete wavelengths that pass a point in one second as the wave goes by As wavelength decreases, frequency increases As wavelength increases, frequency decreases frequency: the number of complete wavelengths that pass a point in one second as the wave goes by

Frequency = wavelengths ÷ time Frequency is measured in Hertz, abbreviated Hz Hertz is the measure of the number of wavelengths that happen per second The formula is: Frequency = measured in hertz Wavelengths = measure in meters, centimeters, nanometers Time = measured in seconds Frequency = wavelengths ÷ time frequency: the number of complete wavelengths that pass a point in one second as the wave goes by

Calculate the frequency A surfer is hanging out in the water and counts a total of 18 wavelengths in 9 seconds. What is the frequency? 18/9 = 2 Hz Answer: 2 Hz

Summary of the models of light Ray Model of Light: Light travels in a straight line Explains how shadows form 2. Particle Model of Light: This model is an extension of the ray model of light the rays are made up of fast moving particles called photons 3. Wave Model of Light: Light travels in waves These waves can bend