(Objective(s): • Warm up(write question and answer in

your notebook)

• How does the size of the slits in a diffraction grating affect the pattern seen? Draw a diagram to illustrate your answer.

P.7D investigate behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect

Reflection and Refraction

Jan 30 – 31, 2012http://player.discoveryeducation.com/

index.cfm?guidAssetId=576E850B-3D90-40B3-999D-

5095C3E085C8&blnFromSearch=1&productcode=US

Objective(s):

• Reflection – the turning back of an electromagnetic wave at the surface of a substance

• The texture of a surface affects how it reflects light

- Diffuse reflection: reflected from a rough, textured surface

- Specular reflection: reflected from smooth, shiny surfaces

P.7D investigate behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect

http://www.physicsclassroom.com/class/refln/u13l1d.cfm

Objective(s):

• Incoming and reflected angles are equal

• If a straight line is drawn perpendicular (normal) to the reflecting surface at the point where the incoming ray strikes the surface, the angle of incidence and the angle of reflection can be defined with respect to the line.

P.7D investigate behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect

Objective(s):

Flat Mirrors• The relationship between the

object distance from the mirror, which is represented by p, and the image distance (the distance the image appears to be behind the mirror’s surface), which is represented as q, is such that the object and image distances are equal.

• Similarly, the image of the object is the same size as the object.

• The image formed by rays that appear to come together at the image point behind the mirror, but never really do, is called a virtual image.

• Image location can be predicted with ray diagrams.

P.7D investigate behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect

Objective(s):

Concave Spherical Mirrors• Concave mirrors focus light

to form real images.• Real images are formed

when rays of light actually intersect at a single point. They can be displayed on a surface; whereas, virtual images can not.

• The radius of curvature, R, is one factor that determines where the image will appear and how large the object will be.

P.7D investigate behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect

Objective(s):

• Image location can be predicted with the mirror equation

where f = focal length

P.7D investigate behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect

Rqp

211

fqp

111

Objective(s):

• Magnification relates image and object sizes

M =

where M = magnificationh’ = image heighth = object heightq = image distancep = object distance

P.7D investigate behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect

Note: Next class, we will look at sign conventions, image orientation and drawing ray diagrams. HW: Read about curved mirrors in your textbook.

o

i

d

d

p

q

h

h

'

Sign Convention

• p, q + center to front side real image• q - formed behind virtual • R, f + center of curvature concave in front of mirror• R, f - center of curvature convex behind mirror• R, f ∞ no curvature flat• h’, h + both above principal axis• h’, h - either is below principal axis

M: Sign Convention

• Upright + virtual• Inverted - real

Objective(s):

Practice Problems:1. The image of a crayon appears to

be 23.0 cm behind the surface of a convex mirror and is 1.70 cm tall. If the mirror’s focal length is 46.0 cm, how far in front of the mirror is the crayon positioned? (45.9 cm)

2. A convex mirror with a focal length of 0.25 m forms a 0.080 m tall image of an automobile at a distance of 0.24 m behind the mirror. What is the magnification of the image? (0.041)

P.7D investigate behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect

Note: Next class, we will look at sign conventions, image orientation and drawing ray diagrams. HW: Read about curved mirrors in your textbook.

Objective(s):

• Refraction – the bending of a wave disturbance as it passes at an angle from one medium into another

• Refraction occurs when light’s velocity changes:

• C water < C air

• C glass < C water

• When light moves from a material in which its speed is higher to a material in which is speed is lower, the ray is bent toward the normal.

• When light moves from a material in which its speed is lower to a material in which is speed is higher, the ray is bent away from the normal.

P.7D investigate behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect

Objective(s):

Index of Refraction – the ratio of the speed of light in a vacuum to the speed of light in that substance

c n = ------

v

where n = index of refraction c = speed of light in vacuum v = speed of light in medium For simplicity, use the value

n = 1.00 for air (actual value, 1.000293)

P.7D investigate behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect

Objective(s):

• Objects appear to be in different positions due to refraction

• Wavelength affects the index of refraction

• Snell’s law determines the angle of refraction

• nisinθi = nrsinθr

P.7D investigate behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect

Note: Table of indices of refraction given in textbook using 589 nm wavelength light traveling in a vacuum.

Objective(s):

• At some particular angle of incidence, called the critical angle, the refracted ray moves parallel to the boundary, making the refraction equal to 90o.

• For angles of incidence greater than the critical angle, the ray is entirely reflected at the boundary. This is total internal reflection.

P.7D investigate behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect

Objective(s): • sin θc = nr / ni for ni > nr

where θc = critical angle

nr = 2nd medium

ni = 1st medium

P.7D investigate behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect

Objective(s):

Practice Problems:1. A light ray of wavelength 589

nm (produced by a sodium lamp) traveling through air strikes a smooth, flat slab of crown glass ( n = 1.52)at an angle of 30.0o to the normal. Find the angle of refraction, θr. (19.2o)

2. Find the critical angle for a water-air boundary if the index of refraction of water is 1.33. (48.6o)

P.7D investigate behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect

Objective(s):

• Note: Next class, we will look at sign conventions, image orientation and drawing ray diagrams. Quiz 1 will be given.

• Homework:1.Read about curved mirrors.2.Complete the practice

problems on refraction.

P.7D investigate behaviors of waves, including reflection, refraction, diffraction, interference, resonance, and the Doppler effect