Post on 17-Dec-2015
Chapter 13 Light and Reflection
Hr Physics
Sound and Light They share several characteristics: They can be described as waves. They use the same v= formula Light is a transverse wave and sound is
compressional. Light is electromagnetic. The electric and
magnetic components are 90° to each other.
Light We only see a small portion of the
electromagnetic radiation (EMR) spectrum, from 400 nm (blue) to 700 nm (red).
Light travels in a straight line at 299,792,458 m/s from a luminous body unless it is refracted (bent), reflected, or absorbed.
Practice Problems
Gamma-ray bursters are objects in the universe that emit pulses of gamma rays with high
energies. The frequency of the most energetic bursts has been measured at around 3.0 x 1021 Hz. What is the wavelength of these gamma
rays?
Practice Problems
1.0 x 10-13 m
Practice Problems
What is the frequency of an electromagnetic wave that has a wavelength of 1.0 km?
Practice Problems
3.0 x 105 Hz
Reflection and Refraction
When light reflects off another body, it is called illuminated.
The sun is a luminous body and the moon is an illuminated body.
Luminous flux (P) The rate at which light is emitted from a
light source is measured in lumen (lm). A 100 W light bulb emits 1750 lm or 130 cd.
Illuminance (E) is measured in lm/m2 or lux (lx) on a sphere surrounding the source.
The area of the sphere around a source is 4r2.
The Law of Reflection
If light falls upon a smooth surface, the ray of light undergoes regular reflection. The angle of incidence to the normal of the plane (1) is equal to the angle of reflection (2).
Mirror ProblemsConcave and Convex
How to form an Image Two rays are needed to form an “image”.
#1 The parallel goes through the focus.
#2 Through the focus goes parallel.
A third ray through the center of curvature bounces straight back is handy for Convex mirrors.
All rays start at the “top” of the object.
Object
Focal PointImage
Concave Mirror
Object Distance (p)Image Distance (q)
f is positive
Focal Point
Object
Convex Mirror
Center of curvature
ImageObject Distance (p)
ImageDistance(q)
f is negative
Mirror equations
1 + 1 = 1
p qf
M = h′ = - q M = + upright, virtual
h p - inverted, real
Concave Practice Problems
Find the image distance and magnification of a concave spherical mirror with a focal length (f) of 10.0 cm when the object distances (p) are 10.0 cm and 5.00 cm. Are the images real or virtual? Are the images inverted or upright? Draw a ray diagram for each case to confirm
your results.
Concave Practice Problems
p = 10.0 cm: no image (infinite q);p = 5.00 cm: q = -10.0 cm, M = -2.00; virtual,
upright image
Concave Practice Problems
A concave shaving mirror has a focal length of 33 cm. Calculate the image position of a
cologne bottle placed in front of the mirror at a distance of 93 cm. Calculate the magnification
of the image. Is the image real or virtual? Is the image upright or inverted? Draw a ray diagram to show where the image forms and how large it
is with respect to the object.
Concave Practice Problems
q = 53 cm; M = - 0.57, real, inverted image
Concave Practice Problems
A concave make-up mirror is designed so that a person 25.0 cm in front of it sees an upright image at a distance of 50.0 cm behind the
mirror. What is the radius of curvature of the mirror? What is the magnification of the image?
Is the image real or virtual?
Concave Practice Problems
R = 1.00 x 102 cm; M = 2.00; virtual image
Concave Practice Problems
A pen is placed 11.0 cm from a concave spherical mirror produces a real image 13.2 cm from the mirror. What is the focal length of the
mirror? What is the magnification of the image? If the pen is placed 27.0 cm from the mirror,
what is the new position of the image? What is the magnification of the new image? Is the new
image real or virtual? Draw a ray diagram to confirm your results.
Concave Practice Problems
f = 6.00 cm; M = -1.20; q = 7.71 cm; M = -0.286; real image
Convex Practice Problems
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? What is the magnification of the image? Is the image virtual or real? Is the
image inverted or upright? How tall is the actual crayon?
Convex Practice Problems
p = 46.0 cm; M = 0.500; virtual, upright image; h = 3.40 cm
Convex Practice Problems
A convex mirror with a focal length of 0.25 m forms a 0.0800 m tall image of an automobile at a distance of 0.24 m behind the mirror. What is the magnification of the image? Where is the
car located, and what is its height? Is the image real or virtual? Is the image upright or inverted?
Convex Practice Problems
A convex mirror of focal length 33 cm forms an image of a soda bottle at a distance of 19 cm behind the mirror. If the height of the image is
7.0 cm, where is the image located, and how tall is it? What is the magnification of the image?
Is the image real or virtual? Is the image inverted or upright? Draw a ray diagram to
confirm your results.
Convex Practice Problems
p = 45 cm; h = 17 cm; M = 0.41; virtual, upright image
Convex Practice Problems
A convex mirror with a radius of curvature of 0.550 m is placed above the aisles in a store.
Determine the image distance and magnification of a customer lying on the floor 3.1 m below the
mirror. Is the image virtual or real? Is the image inverted or upright?
Convex Practice Problems
q = -0.25 m; M = 0.081; virtual, upright image
Convex Practice Problems
A spherical glass ornament is 6.00 cm in diameter. If an object is placed 10.5 cm away from the ornament, where will its image form? What is the magnification? Is the image real or
virtual? Is the image inverted or upright?
Convex Practice Problems
q = -1.31 m; M = 0.125; virtual, upright image
Convex Practice Problems
A candle is 49 cm in front of a convex spherical mirror that has a focal length of 35 cm. What are the image distance and magnification? Is
the image virtual or real? Is the image inverted or upright? Draw a ray diagram to confirm your
results.
Convex Practice Problems
q = -2.0 x 101 cm; M = 0.41; virtual, upright image