Physics- Light

What's the primary source of light?

the sun

Explain how visible objects are visible

Everything that is visible is made visible by the light it absorbs and reflect from its sources

What did scientists think up until Newton and beyond?

UP until the tim of Newton and beyond, most philosophers and scientists thought that light consisted of particles.

What fact was the particle theory supported by?

The particle theory was supported by the fact that light seemed to move in straight lines (more than one) instead of spreading out as waves do.

Describe the photoelectric effect

In 1905, Einstein published a theory explaining the photoelectric effect. This theory says that light consists of particles- massless bundles of electromagnetic energy- later called photons

What is the modern view on light?

The modern view on light is that light has dual nature: part wave, part particle

Describe Olaus Roemer's experiment

Olaus Roemer was the first to try to measure the speed of light in 1675. He did this by measuring the periods of Jupiter's moons. Olaus found that when earth was rotating opposite the moon, Jupiter's moons' period appeared longer than when we were facing

What is the formula for finding the speed of light?

Speed of light= extra distance/ extra time

Describe Albert Michelson's experiment

Another experiment measuring the speed of light was performed by Albert Michelson in 1880. He reflected light on an octagonal block with mirrors on each side (eight sides). The light was reflected from one of the mirrors to a mirror on a hillside a distan

How long does light take to travel from the sun to the earth?

It takes light 8 minutes to travel from the sun to the earth.

How long does it take for light to travel from the earth to the nearest star, Alpha Centauri?

It takes light 4 years to travel from earth to Alpha Centauri.

Light year

A light year is the distance light travels in one year

How long does it take light to travel the universe?

It takes light 100,000 light years (100,000 years) just to travel the universe. Light is VERY fast; the universe is VERY big.

If a galaxy is 10 billion light from earth, and it exploded 5 billion years ago, how long will it take for us to realize the galaxy exploded?

We will not know the galaxy exploded until 5 billion more years.

What is light?

light is energy that is emitted by accelerating electric charges- often electrons in atoms (all matter is made up of atoms!)

What kind of wave does light travel in?

light travels in an electromagnetic wave

Electromagnetic wave

Wave that is partly electric and partly magnetic

Electromagnetic spectrum

Range of electromagnetic waves. Light is a small portion of a broad family of electromagnetic waves.

Infrared

electromagnetic waves of frequencies LOWER than the red of visible light. Think of a heat lamp at Luby's. Can't see those waves because they're infrared!

Ultraviolet

Electromagnetic waves of frequencies HIGHER than that of violet. Think of sunburn! Can't see them because they're ultraviolet

Explain what happens when light hits the object

What happens really depends on if the object is opaque, translucent, transparent. But, overall, when light hits an object, electrons are forced in to vibration. These vibrations are transferred from source (like sun) to object (like uglydoll on bed).

Explain what happens when ultraviolet light shines on glass

Visible light has such a high frequency that if an object is to respond, it must have little inertia. What has little inertia, which can respond to this light? ELECTRONS, which are so small they are able to vibrate this fast! Electrons in glass have a nat

Explain what happens when visible light shines on a glass

If visible light shines on a glass, the energy is reemitted as transmitted light. Come in, go out. (Hence, its transparent)

What is the speed of light?

The speed of light, c= 300,000 km/s

What happens to light's speed when it is absorbed, reflected, or transmitted by objects?

Light's speed slows down during interactions with objects. The light exits the object with the EXACT same speed as it went in, 300,000 km/s, but since it slowed down during the interaction, it's AVERAGE SPEED is less.

What happens when infrared waves hit a glass?

Infrared waves vibrate the ENTIRE structure of the glass! This causes the glass to become warmer (remember during work and collisions some energy turns into heat). So, in sum, glass is transparent to visible light, but not to ultraviolet or infrared.

Opaque

materials that reflect or absorb light. do NOT transmit (that would be transparent)

Explain what happens when ANY light hits an opaque object

In opaque materials, any light, which is absorbed and reflected by atoms and molecules, is turned into kinetic energy by the atoms and molecules (remember, they are moving around within the object). Because of this, the object becomes warmer (remember. du

Explain why metals are shiny

In metals, electrons are NOT bound to a particular atom that's why metals conduct electricity and heat so well. When light shines on metal, it sets these free electrons into vibration. Their energy is NOT shared, but reemitted as visible light! That's why

Ray

a thin beam of light

shadow

formed where light rays cannot reach

umbra

total shadow

penumbra

partial shadow

Explain when a penumbra is formed

A penumbra is formed where some light is blocked, but where other light fills in.

Lunar eclipse

When the moon passes into earth's shadow

Why do stars twinkle?

Stars twinkle because layers of warm and cool air in the night sky bend the starlight

Explain polarized and unpolarized light

A common light source, such as the sun, emits light that is NOT polarized. This is because the vibrating electrons produce light that vibrates in random directions. Polarized light's direction of motion is in one direction. Is a transverse wave polarized?

Explain how light become polarized once it enters sunglasses

Once light passes through a pair of sunglasses, it is polarized. The filters in sunglasses cause it to become polarized because they have a polarization axis. Think of ropes passing through picket fences, where the ropes are light waves, and the fences ar

When does light never go through polarization filters?

NO light what-so-ever gets through polarization filters overlapped at right angles.

What gives you a perception of depth?

The combination of views of both eyes gives you the perception of depth.

Explain how 3-D imaging works

A pair of images can be seen in 3-D when the right eye sees ONLY the right view and the left eyes sees ONLY the left view, like in real life.