PHYSICS FINAL EXAM CH 26 & 28 Flashcards
(14 cards)
What are electromagnetic waves?
These are waves created by the vibrations between an electric and a magnetic field.
What are the characteristics of EM waves?
These waves can travel in a vacuum at the speed of light. They have characteristics of waves like
reflection, refraction, interference, diffraction.
What is the EM spectrum? Name the different components and briefly describe each
The EM spectrum is the entire range of frequencies of electromagnetic radiation and their respective
wavelengths and photon energies.
- Radio: Your radio captures radio waves emitted by radio stations, bringing your favorite tunes. Radio
waves are also emitted by stars and gases in space.
- Microwave: Microwave radiation will cook your popcorn in just a few minutes but is also used by
astronomers to learn about the structure of nearby galaxies.
- Infrared: Night vision goggles pick up the infrared light emitted by our skin and objects with heat. In
space, infrared light helps us map the dust between stars.
- Visible: Our eyes detect visible light. Fireflies, light bulbs, and stars all emit visible light.
- Ultraviolet: Ultraviolet radiation is emitted by the Sun and are the reason skin tans and burns. “Hot”
objects in space emit UV radiation as well.
- X-ray: A dentist uses X-rays to image your teeth, and airport security uses them to see through your
bag. Hot gases in the Universe also emit X-rays.
- Gamma ray: Doctors use gamma-ray imaging to see inside your body. The biggest gamma-ray
generator of all is the Universe.
Compare and contrast transparent, translucent, and opaque materials
Transparent – allows most if not all of the light through it – clear plastic.
- Translucent – partially allows light through it – lamp shade.
- Opaque – blocks light – wood
What is the speed of light?
Symbol is c, and is equal to 3 x 108 m/s
How is the wavelength of light related to its frequency?
The wavelength and the frequency are inversely proportional to each other.
What is reflection?
It is the bouncing of light upon hitting an obstacle.
Describe the law of reflection
The normal line, incident ray, and reflected ray all lie on the same plane. The angle of reflection is
equal to the angle of incidence
Describe the image formed by plane and spherical mirrors. Give examples
Plane mirrors – same size, laterally reversed, same position as the object is in front of the mirror,
upright. Example: regular mirror
- Concave mirrors – can be same size, smaller or bigger, upright or inverted, in front or behind the
mirror depending on object location. Example: dentist’s mirror
- Convex mirrors – smaller, upright, behind the mirror. Examples: grocery mirrors, car’s side mirrors
What is refraction?
Bending of light at the boundary between two surfaces of different densities
What is index of refraction? What is Snell’s law?
The index of refraction is n = c/v. It is a number that tells you the ratio of the speed light in vacuum (c)
to the speed of light (v) in the material
What happens to light as it moves from dense to less dense materials? What about from less dense to denser
materials?
When light moves from dense to less dense materials, the ray moves away from the normal and vice
versa
Describe total internal reflection
This is the complete reflection of a ray of light within a medium such as water or glass from the
surrounding surfaces back into the medium. It occurs when the angle of incidence is greater than the
critical angle.
What is the critical angle?
This is the angle of incidence that provides an angle of refraction of 90-degrees. For example, the
critical angle for diamond to air is 24.4 degrees.
- As shown in the figure, light incident from water refracts at the boundary with air. At the critical angle,
the refracted ray skims the boundary, and at angle of incidences greater than the critical angle, you
would observe total reflection.
