Light Primary Colors

Light is additive. This means that new colors are created by adding more lights of different colors until white light is created from all of the different colors. This concept is used in lighting for plays and concerts.

Separating Light

Prisms are transparent objects, usually made of glass, which can reflect light. "White" light hits the prism on one side moving at a certain speed. When the light goes through the solid material, however, the light is refracted so that light waves with different frequencies leave the prism at different angels; therefore, each separate color of the visible light spectrum is visible.

Rainbows- A Physics Example

The colors of the human visible light spectrum are those that comprise a rainbow, often abbreviated as ROY G. BIV (red, orange, yellow, green, blue, indigo, violet). Rainbows are created when light is reflected off of water and dust particles in the air.

Energy Per Photon

As the diagram from the last post suggested, the color red has the lowest frequency and violet has the highest frequency. This means that because of its shorter wavelength, violet has the most energy per photon, which makes sense since it is located closer to ultraviolet light (UV ray) on the electromagnetic spectrum.

Visible Light Spectrum

As we saw, visible light is only a fragment of the total electromagnetic spectrum. This is where we tie in our knowledge of wavelengths and frequencies: the human eye can only perceive light between 380 nm and 760 nm (400-790 terahertz). These, therefore, are the boundaries for the wavelengths and frequencies of light in the "visible light spectrum."

What You Can See and What You Can't

We cannot see all types of transverse waves. This is a result of the widely varying frequencies of the waves, only some of which the human eye can sense. All of the possible frequencies of the frequencies of electromagnetic radiation are listed as part of the electromagnetic spectrum, only part of which is comprised by visible light.

Frequency Implications

Frequencies are unique measurements of a wave. Waves with different frequencies either sound different (different pitches) or look different (i.e. different colors). For this reason it is very important for us to understand this quality of waves, as it can help us use them in more practical ways.

How Much in How Long

The wavelength of a wave helps determine a wave's frequency. Frequency, in this case, is defined as the number of cycles (1 cycle = 1 wavelength) of a wave that pass by a certain point in a certain amount of time (generally in cycles per second).

Wavelength

The wavelength of a wave is an extremely important and unique aspect because it helps to determine how that wave is perceived, as we will soon see. Wavelength is measured from crest to crest (or trough to trough) on a wave.

Effects of Wave Amplitude

The amplitude of a wave determines how strongly it is perceived. For light waves (trasverse), the amplitude determines the brightness of a color. For sound waves (longitudinal), amplitude determines the loudness (intensity) of the sound being heard.

 

Aspects of Waves

There are certain aspects of waves (both transverse and longitudinal) which affect the way in which they are perceived. These are wavelength, amplitude, and frequency.

Visualizing Longitudinal Waves

It may be hard to picture how a longitudinal wave actually works. A good way to understand this physics concept is to experiment with a Slinky. The way in which this toy works is very similar to the manner in which a longitudinal wave travels - some of the particles compress, only to

transfer their energy on to newly-compressing particles.

Longitudinal Waves

For longitudinal waves, the direction of energy transfer is the same as the movement of the particles. Particles in such a wave hit one another (compress) in order to transfer energy on to the next particles.

Transverse Waves

The transverse wave, which is responsible for the movement of light, looks like this diagram. The molecles in such a wave oscillate up and down, but the overall motion of the transfer of energy is perpendicular to this motion (to the right in this diagram).

Types of Waves

There are two main types of waves: longitudinal and transverse. Sound waves are longitudinal (compression) waves, and light waves are transverse. These types of waves affect how we perceive the world in our everyday lives

Sight and Sound Intro.

Both light and sound travel through waves; however, the two types of waves through which they travel are extremely different. The differences between these waves are what allow for sight and sound.

Friction on Ice

Friction occurs even on smooth surfaces such as ice, otherwise skating on ice would not be possible. When a figure skater skates on ice, it is the friction between the inside of the blade and the ice which causes the resistance that allows for motion in the opposite direction, propelling the skater forward.

Moment of Inertia (cont)

The moment of inertia depends on both the mass of the object and the distribution of this mass around the axis of rotation. For this reason, figure skaters often pull their arms in during a turn in order to decrease their moment of inertia and increase their speed.

Motion Resistance

A spin performed by an ice skater is the result of more than just torque. Inertia, the skater's bodily resistance to a change in state also comes into effect by decreasing the speed of the skater. In situations such as making a turn while ice skating where the motion is rotational, this factor is called the "moment of inertia."

Skating on Ice

Torque is what allows a figure skater to skate on ice. A skater pushes one of his/her feet against the ice in order to exert a torque on his/her body and thereby initiates a spin.

Designing a Door

Torque has to be taken into account in the design and creation of a door. Because the torque of a force is greater when it is applied along a larger distance from the axis of rotation (and therefore the force is more effective) door knobs are placed on the side opposite the door hinges.

Torque, Clarified

It is important to note that torque is not always determined by the total force applied on an object. Instead, it is only the force that is perpendicular to the lever arm that is taken into account in the calculation.

Torque (cont)

The torque of a force is found using this simple formula:
T = Fd, which means that the torque equals the distance from the axis of rotation to the place where the force is applied (d) multiplied by the magnitude of the force (F). Maximizing the torque of a force has many real-world benefits, so being able to calculate it is beneficial.

Intro to Torque

Torque is a rotational force. It is, in a way, a measure of the force causing an object to rotate around a fixed axis.