light what is light? a type of electromagnetic wave type of energy that travels as a wave no medium...
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LIGHT
What is LIGHT?
• A type of electromagnetic wave
• Type of energy that travels as a wave
• NO medium is required
• We see things because light reflects off of them
What is an Electromagnetic Wave?
• A transverse wave• A wave that can travel through space or matter
and consists of changing electric and magnetic fields.– Field-a region around an object that can exert a force
without actually touching the object– Example:magnet
• Waves are produced by the vibration and movement of an electron
How are Electromagnetic Waves Produced?
• Produced by the vibration and movement of an electron
• When an electron changes energy levels, energy is emitted
• The energy is emitted as a particle called a photon
• A stream of photons carries the energy from the electron, as a light wave.
photon
The Electromagnetic Spectrum
Visible Light• We see different wavelengths as different
colors• When all colors are combined, we see
white light• When there are no colors, we see black
Visible Light• Light travels in a straight line• When shining a light, closer objects
appear brighter, this appears for 3 reasons
1. The beam of light spreads out
2. Absorption
3. Scattering
Absorption & Scattering
• Absorption– the air particles around the light absorbs (takes) some
of the energy from the light• Scattering
– Light scatters in all directions– The particles that absorb energy (around the light
source) give off light energy– This makes us able to see things near the light that
are not on the line that the light is traveling– Shorter wavelengths scatter more light than longer
wavelengths.
Law of Reflection
• Law states that:– angle of incidence = angle of reflection– Angle of Light going into surface = angle going out
If the reflecting surface is smooth, then light reflects off of all points at the same angle.
If the reflecting surface is rough, then light reflects off at many different angles.
LIGHT & COLOR
• Light can interact with matter in 3 ways1. Reflected-light rays reflect at angle of incidence
2. Absorbed-energy is transferred to the particles
3. Transmitted- light passes through the matter
• TYPES OF MATTER– Transparent-light is easily transmitted– Translucent-transmits and scatters light– Opaque-does not transmit any light
COLORS of OBJECTS
• The color of an object is determined by the wavelength of color that reaches your eye.
• OPAQUE OBJECTS– When white light hits a colored object, some colors
are absorbed and some are reflected– Only the light that is reflected reaches your eyes, this
is the color that we see• White objects REFLECT ALL colors• Black objects ABSORB ALL colors
• TRANSPARENT OBJECTS– We see the color that is transmitted through the
matter
MIRRORS-----
• Images in mirrors are reversed left to right• Light waves travel in straight lines in all
directions from a light source– An arrow called a ray can represent the path
and direction of the light wave– These rays are used to show the light after it
is reflected or refracted- it shows the change of direction
Mirrors Reflect Light
Mirrors are classified by their shape, –plane, concave, and convex– The shape of the mirror affects the way light
reflects from it and how an image appears
Plane Mirrors
• A mirror with a flat surface• When you look at it, your reflection is upright
and the same size as you are• Images are reversed from left to right• Image appears to be the same distance from the
mirror as in front of it• Mirrors are opaque, light does NOT travel
through them• The image created is virtual-your brain sees
the reflected light and thinks it is straight behind the mirror
Plane Mirrors
Concave Mirrors• Mirrors that are curved inward• Form virtual images• Can form REAL images-image though which
light actually passes, can be projected onto a screen
• Create a ray diagram to decide if an image is real or virtual
Ray Diagram Terms
How to Draw Ray Diagrams
1. Draw a ray from the top of the object parallel to the axis. It will reflect and go straight through the focal point.
2. If the distance between the object and the mirror is more than one focal length, draw a ray from the top of the object through the focal point. The ray will reflect parallel to the axis.
3. If the object is less than one focal length away from the mirror, draw a ray though the top of the object from the focal point and it will reflect parallel to the axis.
Virtual or REAL?
• Draw a ray diagram to answer the question, you need to draw two rays from the top of the object
• If the reflected rays cross in front, of the mirror, a REAL image is formed– The crossing point is the top of the image
• If the reflected rays do NOT cross, trace the reflected rays in straight lines behind the mirror– These lines will cross to show where the image forms– This is a VIRTUAL image
• If the object is placed at the focal point of a concave mirror, NO IMAGE IS FORMED
REAL IMAGE
VIRTUAL IMAGE
CONVEX MIRRORS• A mirror that curves out toward you• All images formed are VIRTUAL and
UPRIGHT and SMALLER than the original
Refraction
• The bending of a wave as it passes at an angle from one medium to another.– This occurs because the speed of light
changes according to the medium – When a wave enters a new medium at an
angle, the part of the wave that enters first begins to travel at a different speed from the rest of the wave.
Refraction and COLORS
• White light is made up of all colors of visible light• Each color has its own wavelength• When white light is refracted, the amount that
the light bends, depends on the wavelength.– Light waves with SHORT wavelengths bend MORE– This allows white light to be separated into different
colors during refraction
• This is why and how rainbows form
Diffraction
• The bending of waves around barriers or through openings– Greatest amount of diffraction occurs when
the opening is the same size as the wavelength or smaller
• Light waves cannot diffract around large obstacles – This is why you can’t see around corners– Light waves always diffract a small amount
InterferenceWhen two or more waves overlap
• Constructive Interference– Resulting wave has a greater amplitude-bright
spots of light• Destructive Interference
– Resulting wave has a smaller amplitude-dark spots or dim light.
Mixing COLORS of Light
• RED, BLUE and GREEN can be combined in different ratios to produce all colors of visible light– Called the Primary Colors– When they are mixed, they make secondary colors
• Mixing Colors of Pigment– Pigment-material that gives a substance color by
absorbing colors of light and reflecting others– This is why we cannot mix red, blue and green paint
to make white paint.
Lenses Refract Light
• Lens- a curved, transparent object that forms an image by refracting, or bending light
• Classified by shape– Convex-thicker in the middle than at the
edges– Concave-Thinner in the middle than at the
edges
Convex Lenses
• Light is refracted towards the center• Light rays enter parallel to axis and are refracted
so that they go through the focus point– Amount of refraction and focal length depends on the
thickness of the lens– Light rays passing through the center of a lens are not
refracted
• Can form REAL AND VIRTUAL images, depends on the focus length and placement of the object
CONVEX LENSES
Concave Lenses
• Light rays enter parallel to the axis and bend away from each other toward the edges of the lens
• The rays never meet• Always form a VIRTUAL image
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