1. 3.2 Models used to explain the properties of electromagnetic radiation
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2. 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:

3. 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

4. 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

5. 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.

6. 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?

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

8. 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

9. 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

10. 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

11. 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 .

12. 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

13. 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)

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

15. 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

16. 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

17. 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

18. 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