Physics

reflection

bouncing back of a particle or wave that strikes the boundary between two media

normal

line perpendicular to a surface

angle of incidence

angle between incident ray and the normal to a surface

angle of reflection

angle between a reflected ray and the normal to a surface

law of reflection

angle of incidence for a wave that strikes a surface is equal to the angle of reflection. This is true for both partially and totally reflected waves

virtual image

image formed through reflection or refraction that can be seen by an observer but can't be projected on a screen because light from the object doesn't actually come to a focus

diffuse reflection

reflection of waves in many directions from a rough surface

reverberation

persistence of soutotal internal reflectionnd, as in an echo, due to multiple reflections

refraction

change in direction of a wave as it crosses the boundary between two media in which the wave travels at different speeds

wave front

crest, trough, or any continuous portion of a two-dimensional or three-dimensional wave in which the vibrations are all the same way at the same time

mirage

floating image that appears in the distance and is due to the reflection of light in Earth's atmosphere

dispersion

separation of light into colors arranged according to their frequency, by intersection with a prism or diffraction grating, for example

critical angle

minimum angle of incidence for which a light ray is totally reflected within a medium

total internal reflection

100%% reflection (with no transmission) of light that strikes the boundary between two media at an angle greater than the critical angle

optical fiber

transparent fiber, usually of glass or plastic, that can transmit light down its length by means of total internal reflection

usually some or all of the wave bounces back into the first medium

What happens when a wave reaches a boundary between two media?

they can be reflected, transmitted, or a combination of both. Waves that are transmitted can be refracted.

What happens when waves interact with matter?

that the angle of incidence and the angle of reflection are equal to each other

What does the law of reflection state?

virtual images

what image do plane mirrors produce?

it is reflected in many directions

What happens when light is incident on a rough surface?

not reflected, absorbed or tansmitted

Sound energy is...

it bends

What happens when a wave travels at an angle changes its speed upon crossing a boundary between two media?

parts of a wave front travel at different speeds

Sound waves are refracted when...

changes in the speed of light, as it passes from one medium to another, or variations in the temperatures and densities of the same medium

What can cause refraction?

air near the surface of the ground must be very hot-light speeds up in hot air and refracts upward

What causes a mirage?

refract differently and bend at different angles

since different frequencies of light travel at different speeds in transparent materials they will...

the sun must be shining in one part of the sky, and the water droplets in a cloud or in falling rain must be in the opposite part of the sky

What's needed in order for you to see a rainbow?

when the angle of incidence is larger than the critical angle

When does internal reflection occur?

it's reflected

What happens to light when it strikes a metal surface?

water- 2% of its energy is reflected and the rest transmitted
glass- 4% of its energy is reflected and the rest transmitted

What happens to light when it strikes glass or water

the path will be the same angle as the incident ray

When light strikes a flat mirror at a certain angle, predict the path of the reflected light

the image is the same distance behind the mirror as the object is in front of it

When you view your image in a plane mirror, how far behind the mirror is your image compared with your distance in front of the mirror?

yes, bc each angle of incidence and reflection have the same angle, the many different angles that incident light rays encounter at the surface cause reflection in many directions

Does the law of reflection hold for diffuse reflection?

rough-different directions
smooth-one direction

contrast the reflection of light from a rough and a smooth surface

a surface may be polished when it's smooth less than about 1/8 the wavelength of the light that falls on it

What is meant by the idea that a surface may be polished for some waves and rough for others?

a) sound becomes garbled bc of multiple reflections of sound called reverberations
b) sound level is lower and the hall sounds dull and lifeless

a) What is the effect on sound when room surfaces are too reflective?
b) too absorbent?

the rooms should have grooves so that sound waves are diffused

What could an acoustical engineer do in designing a room to reduce the sound level?

a) waves reach a boundary of a new medium, they both change direction
b) reflection- waves travel at same speed, occurs when the waves don't go through the new medium but bounce back refraction- when wave goes into new medium waves change speed

a) How are reflection and refraction alike?
b) How are they different?

bc the part of the wave that reaches the new medium first changes speed while the rest of the wave doesn't

When a wave crosses a surface at an angle from one medium into another, why does it "pivot" as it moves across the boundary into the new medium?

ray is perpendicular to the wave front

What's the orientation of a ray in relation to the wave front of a wave?

air near the ground is colder than the air above, so speed of sound is slower near the ground and faster in the warm air above causing the sound waves to bend toward the ground

Why do sounds sometimes carry across a lake better at night than during the day?

a) stars twinkling
b) pencil appearing bent in water
c) air above a hot stove appears to shimmer

What are 3 examples of the effect of refraction that we can see?

a) light waves change speed when light passes from one medium to another
b) through different temperatures of the same medium
c) through different densities of the same medium

What are 3 conditions that could cause refraction?

yes

Does refraction occur for both sound waves and light waves?

no bc refraction is caused by change in speed

If light had the same speed in air and water, would light be refracted in passing from air into water?

yes bc he light paths are reversible for reflection and refraction

if you can see the face of a friend who is underwater, can she see you also?

shallower

Does refraction tend to make objects submerged in water seem shallower or deeper than they really are?

light slows down

What happens to the speed of light as it goes from air to water?

toward the normal

Which way does light bend as it passes from air to water?

high frequencies- bc they are closer to the natural frequency of glass and water, and therefore resonate more than low; more interaction=slower speed (bend more)

As light passes through glass or water, do the high or low frequencies of light interact more in the process of absorption and remission and therefore, slow down more?

blue light (higher frequencies) refracts more bc it slows down more than red light

Why does blue light refract at greater angles than red light in transparent materials?

blue light slows down more than red so blue light is bent more than red, when this happens twice (at the 2 non parallel glass surfaces of a prism) the effect is enough to see the rays dispersed

Explain how a prism separates white light into colors