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Light and Reflection Light and Reflection Chapter 14

Light and Reflection Chapter 14. Characteristics of Light Section 14.1

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Page 1: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Light and ReflectionLight and Reflection

Chapter 14

Page 2: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Characteristics of LightCharacteristics of Light

Section 14.1

Page 3: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Electromagnetic WavesElectromagnetic Waves

Light is made of electromagnetic waves.Take a prism and break up white light into a rainbow

like band of colors. These are all in the visible spectrum.

Red, orange, yellow, green, blue, indigo and violet.ROY G BIV

Page 4: Light and Reflection Chapter 14. Characteristics of Light Section 14.1
Page 5: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Electromagnetic WavesElectromagnetic Waves

The spectrum also includes non-visible electromagnetic waves, such as x-rays, microwaves, radio waves, and radiation.

Because they all are electromagnetic waves they all have similar properties.

Page 6: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Electromagnetic WavesElectromagnetic Waves

Electromagnetic waves are transverse waves consisting of oscillating electric and magnetic fields at right angles to each other.

Oscillate: to have a periodic vibration

Page 7: Light and Reflection Chapter 14. Characteristics of Light Section 14.1
Page 8: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Electromagnetic WavesElectromagnetic Waves

Electromagnetic waves vary depending on frequency and wavelength

All electromagnetic waves move at the speed of light

Page 9: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Electromagnetic WavesElectromagnetic Waves

We will use 3.00 X 108 m/s as the speed of light, c.

The wave speed equation is:

c = f Speed of light = frequency X wavelength

Page 10: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Sample ProblemSample Problem

The AM radio band extends from 5.4 X 105 Hz to 1.7 X 106 Hz. What are the longest and shortest wavelengths in this frequency range?

f 1 = 5.4 x 105 Hz f 2 = 1.7 x 106 Hzc = 3.0 x 108 m/sc = f= c/ f

1 = 5.6 x 102 m

2 = 1.8 x 102m

Page 11: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Light travels in straight lines.Light travels in straight lines.

Light travels in straight lines.• Show the laser on the wall. Put an index card in

the beam. This shows that the light is traveling in a straight line, but you can only see it when it hits something.

• Put some chalk dust in the beam to show it is continuous.

Brightness decreases by the square of the distance form the source

• Show how the size of the dot the laser makes gets bigger as it gets further from the source.

Laser

Page 12: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

The brightness of light is inversely proportional to the square of the distance from the light source.Ex. If you move twice as far away from the light source, ¼ as much light falls on the book.

Page 13: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Flat mirrorsFlat mirrors

Section 14.2

Page 14: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Reflection of LightReflection of Light

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

Page 15: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Clear vs. Diffuse ReflectionClear vs. Diffuse Reflection

Specular reflection: light reflected from smooth shiny surfaces

In specular reflection the incoming and reflected angles are equal (=’)

Diffuse reflection: light is reflected from a rough textured surface

Page 16: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Part 2 - ReflectionPart 2 - ReflectionReflection from a mirror:

Incident ray

Normal

Reflected ray

Angle of incidence

Angle of reflection

Mirror

Page 17: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Reflection of LightReflection of Light

Angle of incidence – the angle between a ray that strikes a surface and the normal to that surface at the point of contact.

Angle of reflection – the angle formed by the line normal to a surface and the direction in which a reflected ray moves

Normal is a line perpendicular to the reflection surface.

Page 18: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

The Law of ReflectionThe Law of Reflection

Angle of incidence = Angle of Angle of incidence = Angle of reflectionreflection

In other words, light gets reflected from a surface at THE SAME ANGLE it hits it.

The same !

!!

Page 19: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Drawing a Reflected Drawing a Reflected ImageImage

Use ray diagrams to show image location

We will find the virtual image (the image formed by light rays that only appear to intersect)

Page 20: Light and Reflection Chapter 14. Characteristics of Light Section 14.1
Page 21: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Drawing a Reflected Drawing a Reflected ImageImage

Draw the object in front of the mirrorDraw a ray perpendicular to the mirror’s surface. Because this

is 0 from normal, the angle is the same from the mirror to the virtual object

Draw a second ray that is not perpendicular to the mirror’s surface from the same point to the surface of the mirror.

Next, trace both reflected rays back to the point from which they appear to have originated, that is, behind the mirror. Use dotted lines when drawing lines that that appear to emerge from behind the mirror. The point at which the dotted lines meet is the image point.

Page 22: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Flat MirrorsFlat Mirrors

Image is VIRTUAL, UPRIGHT, UNMAGNIFIED

Page 23: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Chapter 14Chapter 14

14.3 Concave Mirrors

Page 24: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Concave Spherical Concave Spherical MirrorsMirrors

A spherical mirror has the shape of part of a sphere’s surface. The images formed are different than those of flat mirrors.

Concave Spherical Mirror – an inwardly curved, mirrored surface that is a portion of a sphere and that converges incoming light rays.

Page 25: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Concave Spherical Concave Spherical MirrorsMirrors

The light bulb is distance p away from the center of the curvature, C. Light rays leave the light bulb, reflect from the mirror and converge at distance q in front of the mirror. Because the reflected light rays pass through the image point, the image forms in front of the mirror.

Page 26: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Concave Spherical MirrorConcave Spherical Mirror

When an object changes its location in relation to the mirror, its image changes in location, and form.

Page 27: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Spherical Mirrors - Spherical Mirrors - ConvexConvex

Convex spherical mirror:An outwardly curved, mirrored surface that is a portion of a sphere and that diverges incoming light rays

The focal point and center of curvature are situated behind the mirror.

Page 28: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Spherical Mirrors - Spherical Mirrors - ConvexConvex

Convex mirrors take the objects in a large field of view and produce a small image, but give a the observer a complete view of a large area.

Examples:In stores, the passenger’s side of a car

Page 29: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

ColorColor

White light is not a single color; it is made up of a mixture of the seven colors of the rainbow.

We can demonstrate this by splitting white light with a prism:

This is how rainbows are formed: sunlight is “split up” by raindrops.

Page 30: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Wavelengths of LightWavelengths of Light

Red Light – nm

Green Light - nm

Blue Light - nm

Page 31: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Adding coloursAdding coloursWhite light can be split up to make separate

colors. These colors can be added together again.

The primary colors of light are red, blue and green:Adding blue and

red makes magenta (purple)

Adding blue and green makes cyan

(light blue)

Adding all three makes white again

Adding red and green makes yellow

Page 32: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Seeing colorSeeing colorThe color an object appears depends on the

colors of light it reflects.

For example, a red book only reflects red light:

White

light

Only red light is

reflected

Page 33: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

A white hat would reflect all seven colors:

A pair of purple pants, in addition to being ugly, would reflect purple light

(or red and blue, as purple is made up of red and blue):

Purple light

White

light

Page 34: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Using colored lightUsing colored light

If we look at a colored object in colored light we see something different. For example, consider the outfit below – I mean, from a physics standpoint, not as a fashion choice:

White

light

Shorts look blue

Shirt looks red

Page 35: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

In different colours of light this kit would look different:

Red

lightShirt looks red

Shorts look black

Blue

light

Shirt looks black

Shorts look blue

Page 36: Light and Reflection Chapter 14. Characteristics of Light Section 14.1

Using filtersUsing filtersFilters can be used to “block” out different colours of

light:

Red Filte

r

Magenta

Filter