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