Light and Reflection Light and Reflection

Characterization of Light Light has both a wavelike and particle like nature. Light has both a wavelike and particle like nature. Electromagnetic wave theory: Light is a wave composed of oscillating electric and magnetic fields (electromagnetic wave). Electromagnetic wave theory: Light is a wave composed of oscillating electric and magnetic fields (electromagnetic wave). These waves propagate transversely at right angles to each other. These waves propagate transversely at right angles to each other.

Oscillating Magnetic Field Oscillating Electric Field Characterization of Light

All electromagnetic waves travel at the speed of light (c). All electromagnetic waves travel at the speed of light (c). Electromagnetic waves vary depending on frequency and wavelength. Electromagnetic waves vary depending on frequency and wavelength. These differences account for the broad range in the electromagnetic spectrum. These differences account for the broad range in the electromagnetic spectrum. Characterization of Light

The speed of light in a vacuum = The speed of light in a vacuum = x 10 8 m/s The speed of light in air = x 10 8 m/s The speed of light in air = x 10 8 m/s We use 3 x 10 8 m/s We use 3 x 10 8 m/s

Electromagnetic Spectrum

The same relationship between frequency, wavelength, and speed that exists in sound waves or objects undergoing SHM also holds true for electromagnetic waves. The same relationship between frequency, wavelength, and speed that exists in sound waves or objects undergoing SHM also holds true for electromagnetic waves. Characterization of Light ν = f λ c = f λ

Huygen’s Principle Electromagnetic waves travel in wave fronts. Electromagnetic waves travel in wave fronts. Wave fronts are made up of many wavelets, each containing a “point source”. If you make a line tangent to each point source, you have identified a new wave front. Wave fronts are made up of many wavelets, each containing a “point source”. If you make a line tangent to each point source, you have identified a new wave front. Characterization of Light

 Huygens Principle can describe waves interacting with matter (diffraction) or waves moving in a straight line.  The perpendicular direction in which the wave front is moving is referred to as a “ray”.

Wave front motion as it moves around an object Characterization of Light

Light becomes more spread out and there is less light available per unit area. Light becomes more spread out and there is less light available per unit area. Inverse relationship between brightness and distance. Inverse relationship between brightness and distance. Brightness decreases by the square of the distance from the source. Brightness decreases by the square of the distance from the source. ex. There is ¼ as much light falling on a particular spot 2 m away than there is light falling on the same spot that is 1 m away. (fig 14-4 pg. 525) ex. There is ¼ as much light falling on a particular spot 2 m away than there is light falling on the same spot that is 1 m away. (fig 14-4 pg. 525) Characterization of Light

Waves can be approximated as rays. Waves can be approximated as rays. Brightness of light decreases by the square of the distance from the source. Brightness of light decreases by the square of the distance from the source.

Reflection Refers to the turning back of an electromagnetic wave (light ray) at the surface of a substance. Refers to the turning back of an electromagnetic wave (light ray) at the surface of a substance. Depending on how smooth the reflecting surface is, the reflection will either be diffuse or specular. Depending on how smooth the reflecting surface is, the reflection will either be diffuse or specular.

Reflections off flat surfaces follow 2 simple rules: Reflections off flat surfaces follow 2 simple rules: angle in (incidence) equals angle out (reflection) angle in (incidence) equals angle out (reflection) angles measured from the surface “normal”. angles measured from the surface “normal”. Reflection

Using the basic rules of reflection, we can create virtual images. Using the basic rules of reflection, we can create virtual images. Virtual images are images formed by light rays that appear to intersect. Virtual images are images formed by light rays that appear to intersect. ex. Looking in a mirror ex. Looking in a mirror Image location can be predicted with “ray diagrams”. Image location can be predicted with “ray diagrams”. Reflection

Reflection Ray diagram of mirror image (full length mirror)