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Optical Refraction

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# Optical Refraction - PowerPoint PPT Presentation

Optical Refraction . Optical Density is a property of a transparent material that is inverse to the speed of light through the material. i = angle of incidence. normal. r = angle of refraction. i. incident ray. Air. r. Water. refracted ray.

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Optical Refraction

Optical Density is a property of a transparent material that is inverse to the speed of light through the material.

i = angle of incidence

normal

r = angle of refraction

i

incident ray

Air

r

Water

refracted ray

The ratio of the speed of light in a vacuum to the speed of light in a substance is referred as the index of refraction (n) of that substance.

• the index of refraction between any two substances is the ratio of the speed of light in the incident medium to the speed of light in the refractive medium!

Dutch Physicist Willebrord Snell discovered:

n = ci

cr

n = sin(i)

sin(r)

Snell’s Law

Indices of Refraction

The ratio of the speed of light in a vacuum to the speed of light in the medium:

A ray of light passes from air into water striking at an angle of 65.0˚ with the boundary. Calculate the angle of refraction.

i = 90 - 65.0 = 25.0˚

n = 1.33

sin r = sin i

n

= sin 25.0˚

1.33

r = ?

r = arcsin (.318) = 18.5˚

As the angle of incidence increases, the angle of refraction will increase until the point at which it suddenly becomes 90.0˚--> meaning it is refracted along the boundary.

• When the angle of refraction becomes 90.0˚, the angle of incidence if referred to as the critical angle.
• The critical angle will equal the inverse of the index of refraction:

sin ic = 1

n

1) A beam of light passes from air into an unknown substance. If the angles of incidence and refraction are 31.0˚ and 24.3˚ respectively, what must be the speed of light through this unknown substance?

2) A ray of light passes from diamond (n = 2.42) directly into water (n = 1.33). If the angle of incidence is 17.0˚, what must be the angle of refraction?

1) A beam of light travels from air into alcohol with an incident angle of 25.0˚. If the angle of refraction is 19.5˚, what is the speed of light in alcohol?

2) A diver under water shines a beam of light to the surface with an angle of incidence in the water of 22.0˚. What is the angle of refraction in the air?

3) A ray of light is passed from air into water (n = 1.33) so that the angle of refraction is 28.8˚. What is the angle of incidence?

4) What is the angle of refraction when light passes directly from glass (n = 1.61) into water (n = 1.33) at an angle of incidence of 22.0˚?

5) What is the angle of incidence when light passes from diamond (n = 2.42) into glass (n = 1.53) at a refractive angle of 38.0˚?

6) A beam of light passes from water into diamond making an angle of 55.0˚ with the boundary. What is the angle of refraction in the diamond?

7) A ray of light passes from ice (n = 1.30) to diamond to Lucite (n = 1.50) so that the angle of refraction in the Lucite is 32.0˚. What is the angle of incidence in the ice?

ice

diamond

Lucite

Lens Optics

A lens is a transparent object that bends light rays because of curved surface(s).

Lenses fall into two basic categories depending upon how the light bends after passing through them:

F

1) Converging Lenses :

cause light rays to refract and intersect!

focal length (f)

cause light rays to refract and intersect!

1) Converging Lenses :

focal length (f)

Real ImageNo ImageVirtual Image

2) Diverging Lenses:

Cause refracted light rays to go apart:

F

focal length (f)

** Diverging lenses have a virtual focus and so would have a negative focal length!

Diverging Lens:

cause light rays to refract and diverge!

virtual focus (f)

Virtual Image formed!

Converging Lens Image Formation

f

do

di

1 = 1 + 1

f do di

hi = di

ho do

Diverging Lens Image Formation

Forms virtual images only!

Virtual distances are not directly measurable, and therefore are represented as negative values!

A lens at the 60.00 cm mark on the optical bench produces a real image on a screen located at the 95.00 cm mark. If the focal length of the lens is 12.0 cm, where is the object located on the bench?

A converging lens is used as a simple magnifier to make objects appear 3 times as large. What is the focal length of this lens if it is held 3.00 cm from newsprint that is 3.00 mm tall?

A diverging lens makes an object that is 5.00 cm tall appear half as tall. What must be the focal length of this lens if it is 10.0 cm away from the object?