Mr. Rockensies Regents Physics

When light is seen as a single color, it is considered monochromatic When light has more than one color, it is referred to as polychromatic White light is the result of at least 3 colors, and usually is full-spectrum Full spectrum means that it has all wavelengths of the electromagnetic spectrum. Our Sun emits wavelengths across the entire spectrum.

Coherent Light is monochromatic and all pulses are in phase Monochromatic Coherent

Light is slower than c=3.00x10 8 m/s in all media besides vacuum and air. The degree of bending depends on how much the light slows down. Speed of light in vacuum Speed of light in other medium Index of Refraction = n =c v Typical n values are on the reference tables

n 1 sinθ 1 = n 2 sinθ 2 boundary Medium 1 n 1 Medium 2 n 2 θ1θ1 θ2θ2 θ 1 = angle of incidence θ 2 = angle of reflection Waves bending in a Medium

a b c dd c b a θ 1 = θ c θ 2 = 90° slower medium faster medium In case “c” the refracted ray is right along the boundary – “critical” case. At this point, θ 1 is called θ c – the critical angle and θ 2 is 90°. Find the n value

Based on laws of refraction, a fiber optic cable is designed so that any light that enters cannot leave until reaching an exit at the other end of the cable Fiber Optic Cable We call this phenomena “total internal reflection”, and it occurs when the incident angle is greater than the critical angle – resulting in a reflected ray.

1. Extended Sunset Earth Atmosphere Ray from the Sun Refracted Ray due to the atmosphere, allows us to see the Sun after it has set.

2. Dispersion of Colors in non-dispersive media (vacuum & clean air) all colors have the same speed and bend the same amount in dispersive media (everything else) each color has a slightly different speed and index of refraction Red is the fastest, has the smallest index of refraction, and bends the least.

Receding Source, frequency appears lower (called “Red Shift”) moving source Approaching source, frequency higher (called “Blue Shift”) ( ( ( ( ( ) ) ) ) ) ) ) ) ) )

1.Radar Guns reflected waves are shifted to red by receding object. By comparing the reflected waves to the original waves, the gun calculates the object’s speed gun ( ) ) ( ) ) ( ) ) car v

2. Doppler weather radar – same as radar gun ~ reflecting radio waves off of air masses/clouds. 3. Astronomy – stars are made of Hydrogen + Helium which have characteristic bright line spectra at known frequencies: Shifted lines indicate that a star is either approaching or receding from us

When we observe light from other galaxies, all lines are red shifted – What would this imply? All galaxies are moving away from us – therefore the universe is expanding

We had said that when waves diffract they bend around corners: Light will exhibit this same behavior. As a result of this bending, we can see spaces of light and dark when light passes through two or more openings that are placed near each other.

If light passes through a boundary with two or more openings, we will see bands of light and dark appear on a surface beyond that barrier. Young’s Double Slit Experiment

Because light is a transverse wave, it can become polarized. Light can also become polarized by reflecting off of a shiny surface – “glare”

Remember, if light passes from a faster medium into a slower medium (i.e. air into anything else), the refracted ray should be bent towards the normal. If light passes from a slow medium into a faster one (i.e. diamond into anything else) then the refracted ray should bend away from the normal. When trying to find the critical angle, always remember that θ 2 MUST be 90°, and therefore sin θ 2 = 1. You can find the velocity of light in ANY medium as long as you have its n value (index of refraction). Use n=c/v ! When measuring the angle of incidence/refraction ALWAYS MEASURE FROM THE NORMAL!! When a wave moves from one medium into another, its speed and WAVELENGTH change, not frequency (the color stays the same) PRACTICE, PRACTICE, PRACTICE!!!