Unit 09 Assessment Guide

Under Construction Poster.pdf

What should I know?

Changes in the electric field induce changes in the magnetic field and vice versa. These changes are created by the acceleration of electrical charges.
Energy is transmitted through the electric and magnetic fields in the form of electromagnetic waves.
Given that the medium is a coupled pair of fields, electromagnetic waves do not require a material medium to propagate.
Waves that move through the electromagnetic fields travel at 300 000 000 m/s. Like all waves, their frequency and wavelength are inversely related.
The absorption and re-emission of light waves by the electrons in a material medium takes time. While light travels at 300 000 000 m/s between atoms, the time required to be absorbed and re-emitted by atoms makes light's average speed through a transparent medium lower than the speed of light in a vacuum.
The energy of electromagnetic waves is contained in their frequency. The higher a wave's frequency, the more energy it contains.
The energy of a light wave can be thought of as a particle -- a photon. Therefore, the nature of light is complex, being part wave and part particle.
As a whole, electromagnetic waves are the same phenomenon, varying only in the energy they contain, represented as their frequency or wavelength. All types of electromagnetic waves are described on a spectrum, from low energy to high.
For convenience, humans break the continuous electromagnetic spectrum into seven sections, making up seven different general types of electromagnetic waves: from low to high energy, radio waves, microwaves, infrared waves, visible light waves, ultraviolet rays, x-rays and gamma rays.
Humans have learned to use each type of electromagnetic radiation to learn more about the Earth and the universe and to improve quality of life.
The Sun radiates the most in the visible spectrum. While visible light is affected by it, the Earth's atmosphere best allows transmission of waves in the visible light spectrum.
Human eyes sense visible light in two ways: rod cells in the retina sense the level of light, giving an image in grayscale; and cone cells in the retina sense the levels of red, blue and green.
Colors in the spectrum that are not red, blue or green or that are not in the spectrum (i.e., pink or brown) are assembled from combinations of colors in the brain.
Objects appear to have the color that they have due to one of three processes: (a) emission -- they produce their own light; (b) reflection -- they selectively reflect light from other sources; or (c) transmission -- they transmit light.
Some objects appear to be certain colors due to a process of selective absorption of some wavelengths of light and the reflection of the remaining light. For example, a shirt that appears to be red absorbs the blue, green and yellow wavelengths of light and reflects the red wavelengths.
Filters selectively absorb some wavelengths of visible light and transmit others.
The sky appears to be blue due to the higher probability of scattering of short wavelengths of light by the O2 and N2 molecules in the atmosphere.
Water appears to be blue-green due to H2O's absorption of long wavelengths.
When a light wave is reflected, the angle it forms with the perpendicular of the surface it hits -- the angle of incidence -- is equal to the angle it reflects off that surface. This is the law of reflection.
The amount that light rays bend when entering a new medium can be predicted through an analysis that includes a comparison of the average speeds of light in the two media.
Curved mirrors and curved lenses can focus or spread out the light, depending on the type of curvature.
The image formed by mirrors and lenses can be predicted and analyzed through the use of a ray diagram.
An image can be described using four key components, with the acronym LOST: location, orientation, size and type (meaning real or virtual.)
The location of an image when using a lens can be determined from the distance of the object from the lens and the focal length of that lens.
Light rays falling at an angle on the surface of a transparent material will appear to bend at that boundary due to a change in the average speed of the light as it moves through the new material. This bending is called refraction.
The amount of refraction that occurs is dependent on the average speeds of light on one side of the medium boundary and the other. The greater the difference, the greater the apparent bend in the light ray's path.
Lenses are objects designed to use the refraction light rays experience to form images.

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