Monthly Archives: December 2017

The Magic of Light

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Refraction is the bending of light waves and occurs when a wave passes from one medium to another. In this case, the penny is originally in the bottom of the cup without any water and is not visible to the camera. As water is added, the light is refracted and the penny is “magically” brought into view without the camera being moved. The penny we see at the end is a virtual image as the penny (object) is in the same spot it started.

Every transparent medium has its own index of refraction. At first, there is no bending of light as there is only one medium and that is air. The greater the index of refraction, the greater the change in direction of light. Water has a greater index of refraction than air. Therefore, once water is added to the cup, the penny will come into view because the light is now bending as it passes through a different medium. The penny appears to keep moving as the water level rises because as the depth of the water increases, the angle of refraction increases. The angle of incidence remained the same as the camera did not move. Only the angle of refraction increased as the water depth rose.

Wave Interference Activity: Constructive and Destructive Interference

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Constructive Interference

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Constructive interference is when a crest from one source meets a crest from another source, the energies combine to displace the medium (the energies are additive). In other words, when the two crests meet, they produce a single amplitude equal to the sum of the two individual amplitudes. The same thing occurs when trough meets trough. When the crests of the waves line up, there is constructive interference. Often, this is described by saying the waves are “in-phase”. In the first video, we put the slinky on the ground and flicked the same way to represent the crest meeting the other crest. The same thing occurred in the second video except we flicked the other way to represent the trough meeting another trough.

Destructive Interference

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Destructive interference is when a crest and trough meet the energies combine to work against each other- they tend to cancel out. The sum of two waves can be less than either wave and can even be zero. When the crests of the wave in one wave match up with the troughs of the wave in the other, the waves are said to be “out-of-phase”. In this video, the slinky is flicked 2 separate ways to represent a crest and a trough. When they meet, they

Exploring Waves Lab

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Pulse Wave

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A pulse wave is a single disturbance that is non-repeating and has one major crest. It often refers to some type of one-time disturbance. A pulse has a velocity and an amplitude but since there is only one crest, there is no frequency or true wavelength, although the width of the pulse relates to its wavelength. To measure a pulse wave’s speed, we use v=d/t.

Periodic Wave

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This type of wave repeats at regular intervals and requires regularly recurring disturbances. Periodic waves are usually characterized by their amplitude, frequency, and wavelength. A wave whose displacement has a periodic variation with time or distance or both.

Transverse Wave

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This type of wave occurs when the spring is pulled sideways. It’s a moving wave that consists of oscillations in which the direction of displacement is perpendicular to the direction of propagation. Transverse waves may occur on a string, on the surface of a liquid, and throughout a solid. Transverse waves cannot propagate in a gas or a liquid because there is no mechanism for driving motion perpendicular to the propagation of the wave.

Longitudinal Wave

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A longitudinal wave is one in which the direction of displacement is the same as (parallel) the direction of propagation. It involves a wave consisting of a periodic disturbance or vibration that takes place in the same direction as the advance of the wave.