Physical Science for Teachers Exam #2

What are waves?

●Waves are disturbances that transfer energy from place to place.

●Many waves require a medium to travel on or through. (Air, Water, Solids)

●Waves DO NOT move matter! Waves ONLY move energy.

Mechanical Waves

●Any wave that does require a medium is called a mechanical wave.

●Two types of mechanical waves are transverse waves and longitudinal

Transverse Waves

●Transverse waves move the medium at right angles to the direction in which the wave moves

What are the four parts of a transverse wave?

Wavelength, crest, trough, amplitude

Longitudinal Waves

●Longitudinal waves move parallel to the direction in which the wave moves.

●Sometimes called “compression” waves

Parts of a Longitudinal Wave

Compression, wavelength, rarefaction, Amplitude (how squished it is)

Properties of a wave (amplitude)

●The amplitude of a transverse wave is the maximum distance the medium moves up

and down from its rest position.

●The amplitude of a longitudinal wave is the measure of how compressed the compression is.

○Dense compressions = high amplitude

Low vs. High Amplitude

PROPERTIES OF A WAVES (WAVELENGTH)

●Transverse wave = Distance from crest to crest or trough to trough.

●Longitudinal wave = Distance from compression to compression or rarefaction to rarefaction

PROPERTIES OF A WAVES (FREQUENCY)

●The amount of complete waves that pass a certain point in a certain amount of time. (usually seconds)

○ Is determined by wavelength and wave speed.

PROPERTIES OF A WAVES (FREQUENCY)

• Frequency is measured in a unit called hertz (Hz)

• Hertz is named after Heinrich Hertz, the German scientist who discovered radio waves

in the 1880’s.

Magnetism

Magnetism occurs because of electrons and how they travel around the nucleus of the atom. The spinning electrons form tiny magnetic forces. If the electrons in an object spin the same direction, you will get a magnetic force.

Magnetism is the force of attraction or repulsion between magnetic poles.

Moving Electrons

Electrons (e-)

The atoms within most materials have paired up electrons spinning in opposite directions so the magnetic field that is created by one is cancelled out by the other.

Some materials like iron, nickel, and colbalt have a single electron or pair of electrons that spin in the same direction creating a magnetic field or a small atomic magnet.

Magnets

A magnet has two ends called poles (dipoles), where the magnetic force is the strongest.

No matter how many times a magnet is broken, each piece always has a north pole and a south pole.

There is no such thing as a monopole.

Electricity

a fundamental form of energy that can occur naturally (ex. lightning) or is produced (ex. generator) and that is expressed in terms of the movement and interaction of electrons.

Electricity Starts with Atoms

Atoms contain protons with a positive charge (+), electrons with a negative charge (-), and neutrons with no charge.

Electricity occurs from the differences in charges.

Insulators

Insulators are materials that do not allow electrons to easily move from place to place.

Examples: Rubber, Plastic, Wood, Skin

Conductors

Conductors are materials that do allow electrons to move easily from place to place.

Examples: Copper, Aluminum, Water

Electric Force

A force is a push or a pull caused by electric charges.

An electric force is the attraction or repulsion like and unlike charges have for each other.

Opposites attract!

Electric Field

An electric field is the area around an electric force where the charge can be felt.

The electric field gets stronger as you get closer to the source of the electric force.

Static Cling

When two objects – such as your hair and the balloon – rub together, one loses some of its electrons to the other.

One object will become positively charged.

One object will become negatively charged.

Then, opposite charges are attracted to each other.

Electric Discharge

Electric Discharge is the rapid movement of excess charge from one object to another.

Lightning happens due to an electrical imbalance between the storm clouds and the ground. They can also happen within the clouds.

Electric Current

Electric current is a steady continuous flow of electricity.

Unlike electric discharge which is a short burst of electricity

Electric current will only flow through an electric circuit.

Electricity in a circuit behaves much like water in a closed system.

Amperes (Amps)

Amps is the unit given to the measurement of the rate of flow of electric current.

The greater the electrical flow, the greater the amperage.

Voltage

Voltage is the measure of the amount of electrical potential energy.

The stronger the electrical “push” the larger the voltage.

Resistance

Resistance is the measure of how difficult it is for electricity to flow through a material.

They slow the flow of electrons

Resistance is measured in a unit called OHMS.

The amount of electrical resistance is dependent on 4 things:

The type of material

The length of a conductor

The width of the conductor

The initial Voltage

Circuit

A circuit is a closed conducting loop.

An electric current is only able to flow through a closed system.

Series Circuits

A series circuit has only one path for the electric current to follow.

When any part of the electrical path is broken, electricity will no longer flow.

Parallel Circuits

A circuit that provides more than one path for electricity to follow.

Houses, schools, etc. are wired using parallel circuits.

Fuses and Breakers

Fuses and breakers limit the amount of electricity flowing through a circuit.

Electrons

Protons and Neutrons are fixed in the nucleus of the atom and cannot be moved.

However, electrons are able to move from atom to atom.

Electric Power

The rate at which electrical energy is converted into other forms of energy.

Electrical power is measured in Watts.

What is Sound?

Sound is vibration.

Sound travels in the form of longitudinal waves through different mediums.

• It is a mechanical wave so it requires a medium.

How Sound Travels

The longitudinal waves of sound travel as compressions of air caused by the vibration of air.

Sounds in Solids, Liquids, and Gasses

Sound waves require a medium

Sound travels through solids, liquids, and gasses.

Sound travels fastest when molecules of the medium are closer together.

Sound cannot travel in the vacuum of space because the molecules are too far apart.

The Speed of Sound

The speed of sound depends on the density, elasticity, and temperature of the medium the sound travels through.

• Elasticity is the ability of a material to bounce back after being disturbed. (The molecules of a solid return to their original position quickly after a disturbance)

Why does sound travel slower in cold air vs. warm air?

The colder the molecules of a substance, the slower those molecules move. Cold air molecules move slowly and do not return to their original position (elasticity) as quickly as warm air molecules.

The Speed of Sound (and Density)

Sound travels faster through objects that are denser, which is why sound travels better through a solid than a liquid.

Sound travels better in a liquid than through air.

Properties of Sound (Intensity)

The volume of a sound depends on its INTENSITY.

The INTENSITY of a sound is the amount of energy a wave carries.

The closer you are the source of sound the greater the INTENSITY.

Low vs. High Intensity

Properties of Sound (Intensity) pt. 2

The loudness of sounds is measured in Decibels (dB).

The decibel scale is logarithmic. Each jump in 10 dB equals a 10 fold increase in the volume of a sound.

• 50 dB = 10 times louder than 40 dB

As the amplitude of the sound wave increases, the intensity of the sound increases.

Properties of Sound

The pitch of a sound is the human perception of the frequency of a sound.

• Sounds with low pitch have a low frequency

• Sounds with a high pitch have a high frequency

Pitch

The length of an instrument affects the pitch of the sound that comes out of the instrument. (Shorter instrument, higher pitch)

The same is true for finger placements on an instrument. Covering holes in the instrument makes the vibrating column of air shorter or longer.

The Doppler Effect

The Doppler effect is the change in frequency of a wave as its source moves in relation to the observer.

• As a sound source moves toward you, the waves are squished creating a higher pitch.

• As the sound source moves away from you, the waves are stretched creating a lower pitch.

Frequencies

Every material or object has a particular set of frequencies at which it vibrates.

When a material or object is made to vibrate at its natural frequency it is called resonance.

Quality of Sound (Acoustics)

Acoustics is the study of how sounds interact with each other and the environment.

• Certain acoustical environments help eliminate destructive interference.

• Other acoustical environments create an environment with little or no reflection of sound waves.

Reverberation and Echo

Reverberation is the reflection of sound waves.

• Objects reflect sound differently depending on their shapes

When a sound reflection is repeated, it is called an echo.

Practical Uses of Reverberation

Echolocation is the use of reflected sound waves to determine distances to locate objects.

• Bats, dolphins, and whales use echolocation to find their food.

• Bats can use frequencies up to 100,000 Hz (humans can hear up to 20,000 Hz)

Sonar uses the reflection of sound waves to locate objects under water.

• Objects of different densities reflect sound waves differently.

A picture created by a device that uses reflected sound to create that picture is called a sonogram.

The Electromagnetic Spectrum

The Electromagnetic Spectrum - Waves

Electromagnetic waves have two parts

-electric part

-magnetic part

Electromagnetic waves can be described by their frequency (number of waves in a specific amount of time)

• Radio waves have the lowest frequency

• Gamma waves have the highest frequency

All electromagnetic waves travel at the speed of light (300,000 km/s in a vacuum)

• Light from the sun takes about 8 minutes to reach the earth.

Electromagnetic waves do not need a medium to travel through.

Radio Waves - #1 on Spectrum

Radio waves have the longest wavelength in the EM spectrum.

They are useful for transmitting radio and television broadcasts.

Microwaves - #2 on Spectrum

These have a shorter wavelength and a higher frequency than radio waves.

• Cell phones and microwaves use this type of EM radiation.

Infrared Waves - #3 on Spectrum

Have wavelengths shorter than radio and microwaves.

This type of radiation can be felt in the form of heat (the more heat something has the more infrared radiation it emits).

• Remote controls use infrared radiation and certain cameras have the ability to capture this type of radiation and turn it into a “thermogram.”

Visible Light - #4 on Spectrum

The only portion of the EM spectrum that can be seen by humans.

Each color has its own unique wavelength

It is a very small portion of the entire spectrum.

Ultraviolet Waves (The Good) - #5 on Spectrum

Have wavelengths just shorter than visible light

• Enable your body to create Vitamin D

• Used to disinfect food and air

Ultraviolet Waves (The Bad) - #5 on Spectrum

Shorter wavelength and higher energy UV rays (Cause of sunburn and skin cancer)

Ozone layer absorbs the majority of these

CFC’s (chlorofluorocarbons) break down the ozone layer allowing more harmful UV light to reach the earth.

X-Rays - #6 on Spectrum

Have a shorter wavelength and carry more energy than UV light.

Have enough energy to pass through most types of matter depending on the density (which is why it is useful for medical imaging)

Large doses can be dangerous by mutating DNA

Gamma Rays - #7 on Spectrum

The highest energy wave and shortest wavelength in the EM spectrum

Have the highest penetrating power and can travel through most materials

Given off by nuclear reactions that can quickly damage human body and cause cancer (Chernobyl)

When Light Strikes an Object

Light can be TRANSMITTED or pass through an object.

Light can be REFLECTED or bounce off an object.

Light can be ABSORBED in which the light energy is “taken in” (usually transfers into thermal/kinetic energy)

How Light Passes Through

The amount of light that passes through an object depends on what type of object it is.

Transparent – All light passes through (window, glasses)

Translucent – Some light passes through (sunglasses, tissue paper)

Opaque – No light passes through (brick, metal)

Reflection

Two Types: Diffuse and Specular

Diffuse Reflection

When light strikes an object and bounces off in all different directions.

• Typically occurs when light strikes a bumpy, rough, or unsmooth surface.

Specular Reflection

When light waves bounce off an object at a predictable angle.

• Typically occurs on flat smooth surfaces like mirrors or still water.

Refraction

When light bends as the wave changes speed as it enters or exits a new medium.

Light and Color

Light is responsible for the presence of COLOR. Without light there is no color.

• Try going into a dark room and identifying the colors of different objects.

White light is made of all the colors of the rainbow.

• We can use a prism to show this.

The color of different objects is determined by the wavelengths of light that the object reflects and absorbs.

Three Types of Mirrors

Plane, Concave, and Convex

Plane Mirror

A flat reflective surface that produces a image upright and of the same size.

Concave Mirror

A reflective surface that curves inward like the inside of a bowl.

• Reflects light to a focal point.

Thinner in the center and causes the light to diverge.

• Sometimes used in eyeglasses

Convex Mirror

A mirror with a reflective surface that curves outward like the outside of a bow.

• Reflects light outward and gives an image smaller than the actual object

Electrons

Protons and Neutrons are fixed in the nucleus of the atom and cannot be moved.

However, electrons are able to move from atom to atom.