Chapter 22 Reflection and Refraction of Light 1. Dual nature of light 2. Geometric optics 3. Reflection and Refraction 4. Dispersion 5. Huygen’s Principle 6. Total Internal Reflection

A Brief History of Light 1000 AD It was proposed that light consisted of tiny particles Newton Used this particle model to explain reflection and refraction Huygens 1678 Explained many properties of light by proposing light was wave-like

A Brief History of Light, cont Young 1801 Strong support for wave theory by showing interference Maxwell 1865 Electromagnetic waves travel at the speed of light

A Brief History of Light, final Planck EM radiation is quantized Implies particles Explained light spectrum emitted by hot objects Einstein Particle nature of light Explained the photoelectric effect

The Particle Nature of Light What is a photon? How do I calculate its energy? Can photon have a wave nature? What about experiments to test such theories? Can a single experiment test dual nature of light?

Ray Approximation & Geometric Optics What is a wave front? What is a Ray? What is the purpose of a ray?

Specular and Diffuse Reflection

Law of Reflection What is it?

Example 1. Two mirrors make an angle of 120° with each other. A ray is incident on mirror M 1 at an angle of 65° to the normal. Find the angle the ray makes with the normal to M 2 after it is reflected from both mirrors

Refraction of Light What is refraction? Snell’s Law

Two cases of Refraction

The Index of Refraction What is index of refraction? How do I calculate it? What are its units? Some typical examples What happens when light passes from one medium to another? An alternate formula

Some Indices of Refraction

Example 1. An underwater scuba diver sees the Sun at an apparent angle of 45.0° from the vertical. What is the actual direction of the Sun?

Example 1. Find the speed of light in flint glass.

Dispersion What is dispersion? Wavelength vs. n for visible light. How does Snell’s law play into this?

Refraction in a Prism What is angle of deviation, δ?

Example 1. The index of refraction for violet light in silica flint glass is 1.66 and that for red light is What is the angular dispersion of visible light passing through a prism of apex angle 60.0°, if the angle of incidence is 50.0°.

Prism Spectrometer What is a spectrometer? How do we use it? What is a spectrum? What is it useful for?

Reflection, Refraction and the Rainbow Why do we see the rainbow?

Kirchhoff’s Laws of Radiation (1) 1.A solid, liquid, or dense gas excited to emit light will radiate at all wavelengths and thus produce a continuous spectrum.

Kirchhoff’s Laws of Radiation (2) 2. A low-density gas excited to emit light will do so at specific wavelengths and thus produce an emission spectrum. Light excites electrons in atoms to higher energy states Transition back to lower states emits light at specific frequencies

Kirchhoff’s Laws of Radiation (3) 3.If light comprising a continuous spectrum passes through a cool, low-density gas, the result will be an absorption spectrum. Light excites electrons in atoms to higher energy states Frequencies corresponding to the transition energies are absorbed from the continuous spectrum.

The Spectra of Stars Inner, dense layers of a star produce a continuous (blackbody) spectrum. Cooler surface layers absorb light at specific frequencies. => Spectra of stars are absorption spectra.

Christian Huygens 1629 – 1695 Best known for contributions to fields of optics and dynamics Deduced the laws of reflection and refraction Explained double refraction

Huygen’s Principle What is Huygen’s principle? How do I apply it for plane waves? How do I apply it to spherical waves? What is the difference between spherical and plane? Why do I even need to know it?

Total Internal Reflection What is Total internal reflection? What is critical angle? How do I calculate it? When is total internal reflection possible?

Example 1. A small underwater pool light is 1.0m below the surface. The light emerging from the water forms a circle on the water surface. What is the diameter of this circle?

Total Internal Reflection and Fiber Optics Applications Surgical techniques Telecommunications Industry What are the advantages? Noise Light loss