Physical Science EOCT Review Domain IV Waves, Electricity and Magnetism

Parts of a Wave

Mechanical (Longitudinal) Waves Examples are sound waves and slinkys

Electromagnetic Waves (Transverse) Electromagnetic waves are transverse waves which have both an electric and and magnetic effect. The energy of the photons is directly proportional to the frequency.

Light Light is a form of electromagnetic radiation (EM) EM spectrum shows the forms of radiation in order of increasing frequency (and energy) and decreasing wavelength

Color of Light We see different colors depending on the frequency of light emitted or reflected This is the reason blue flames are hotter than yellow. Blue has a higher frequency so more energy.

Sample Question How are the frequency and wavelength related to the energy carried by waves? Answer: Higher frequency waves have more energy while longer wavelength waves have less energy. Frequency and energy are directly related while wavelength and energy are inversely related. Radio waves (long wavelength) have less energy than gamma waves (high frequency).

Sample Question How are frequency and wavelength related? Answer: Frequency and wavelength are inversely related. High frequency waves have short wavelengths.

Electromagnetic Wave (EM) versus Mechanical Wave EM WAVE does not require matter to transfer energy CAN travel through a vacuum example: light MECHANICAL WAVE does require matter to transfer energy CANNOT travel through a vacuum example: sound

Sample Question Make a Venn Diagram to Compare electromagnetic and mechanical waves. Sample Answer: Electromagnetic waves (light) do not require matter to transfer energy while mechanical waves (sound) require matter to transfer energy. In other words, EM waves will travel in a vacuum while mechanical waves will not.

Reflection of Light When light strikes a boundary, it reflects. The angle at which the wave approaches a flat reflecting surface is equal to the angle at which the wave leaves the surface (like a bounce pass of a basketball). Reflection results in image formation.

Diffraction We say that the wave bends around the barrier, or that it changes directions.  Where the wave was traveling in a straight line before passing the barrier, it is now 'bent' or it changed direction after passing the barrier. DIFFRACTION of a wave is the bending or redirection of the travel of the wave when it passes a barrier without changing the medium in which the wave is traveling.

Refraction of Light Light waves travel faster in air than in water and slower in glass than water. More dense = slower light When light enters a different medium, speed changes and it bends. Bending of light due to change in speed = REFRACTION

Sample Question Reflection only Refraction only Both Reflection and Refraction Neither Reflection or Refraction The correct answer is “C” because some The light will be reflected some will be absorbed And therefore refracted

Sound and mediums Sound travels fastest through solids. This is because molecules in a solid medium are much closer together than those in a liquid or gas, allowing sound waves to travel more quickly through it. In fact, sound waves travel over 17 times faster through steel than through air. The exact speed of sound in steel is 5,960 meters per second (13,332 mph)! But, this is only for the majority of solids. The speed of sound in all solids are not faster than in all liquids. Remember that Density is the key to how Fast it travels!

Wave Interference CONSTRUCTIVE the phenomenon which occurs when two waves meet while traveling along the same medium constructive = waves add to produce a larger wave destructive = waves cancel to produce a smaller wave DESTRUCTIVE

The Doppler Effect observed whenever the source of waves is moving with respect to an observer an apparent change in frequency occurs toward = higher frequency away = lower frequency

Electricity Electrons carry a negative charge. Lost electrons = positive charge Gained electrons = negative charge REMEMBER: Like charges repel Opposites attract

Static Electricity 3 causes: Friction Conduction Induction If you charge a balloon by rubbing it on your hair, it picks up extra electrons and has a negative charge. Holding it near a neutral object will make the charges in that object move. If it is a conductor, many electrons move easily to the other side, as far from the balloon as possible. If it is an insulator, the electrons in the atoms and molecules can only move very slightly to one side, away from the balloon. In either case, there are more positive charges closer to the negative balloon. Opposites attract. The balloon sticks.

Electrical Circuits Current flows in a closed circuit SERIES Current flows in a closed circuit Two types of circuits: Series (single path) Parallel (many paths) PARALLEL

2 types of electrical currents Alternating Current AC have electrons that can change direction a gasoline-driven generator is an example Direct current DC Means to move continuously in the same direction Car Batteries is an example Ohm’s Law Relates current, voltage and resistance

Sample Question The correct answer is “B”

Electromagnet One can make an electromagnet with a nail, battery, and wire When current flows through the coiled wire, the nail becomes magnetized. The more wraps-the greater the energy.

Electric Generators Faraday discovered that if an electric conductor, like a copper wire, is moved through a magnetic field, electric current will flow (be induced) in the conductor. So the mechanical energy of the moving wire is converted into the electric energy of the current that flows in the wire. This is called electromagnetic induction

Sample Question The correct answer is “A”

Sample Question   When a loop of wire is turned in a magnetic field, electrical charges move through the wire, creating an electrical current. This is the basis for an electric generator, so answer D is correct.

Figure Reference Distance versus Time Graph figures: source unknown Forces figure: retrieved from http://www.glenbrook.k12.il.us/gbssci/phys/CLass/newtlaws/u2l2c1.gif Determining the Net Force figure: retrieved from http://www.glenbrook.k12.il.us/gbssci/phys/CLass/newtlaws/u2l2d11.gif Newton’s Laws, Gravity, Work, Types of Mechanical Energy, Conservation of Energy, Light, Interference, and Doppler Effect figures: retrieved from http://www.physicsclassroom.com Electrical Circuits figures: retrieved from http://www.autoshop101.com/trainmodules/elec_circuits/circ101.html Electromagnet figure: source unknown