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Index of refraction
The velocity of light in media, such as water and glass, is slower than its velocity in vacuum, c=3.00x10^8 m/s.
Index of refraction: dimensionless material constant defined as the ratio of the velocity of light in free
space to its value in the medium: v
c n
From table 23-1: Velocity in light of ethyl alcohol (n=1.36) is:
s
m 0.74c 2.22x
c n
c v ^8
Law of Refraction (Snell’s Law)
n 1 sin 1 n 2 sin 2
Light bends towards the normal ( 1 > 2 ) when going from smaller to higher index of refraction media (n 1 <n 2 ). The reverse is true ( 1 < 2 ) when light travels from higher to lower index of refraction media (n 1 >n 2 ).
Total Internal Reflection
If light travels from higher to lower index of refraction media (n 1 >n 2 ), there is a critical angle c , such that if
1 >c , light is totally internally reflected in media n 1.
1
2 c (^) n
n sin (NOTE: when 1 =c , 2 =90)
Air
Water
Thin Lenses
Transparent material (glass, plastic) with two spherical surfaces where their diameter is less than the radii of curvature. Converging lens: single or double convex shaped object with its center thicker than its edges. Parallel rays from the left converge at the focal point on the right
Diverging lens: Single or double concave shaped object with its center thinner than its edges. Parallel rays from the left result in diverging rays on the right.
Converging lens: Focal length is positive (f>0)
(i) Object placed beyond focal point on one side (left) of lens: image is real (di >0) and inverted (m<0) and appears on opposite side (right)
(ii) Object at focal point (left) will yield parallel light ( di ) on opposite side of lens (right)
(iii) Object within focal point: image will be virtual (di<0) and upright (m>0) on same side of lens as object. Image is also larger than object.
Diverging lens: Focal length is negative (f<0)
Image is virtual (di<0) and upright (m>0) on same side of lens as object (image also smaller in size than object)
