Download Waves Review

Physical Science EOCT Review
Physics – Waves, Electricity, and Magnetism
To meet standards, students should be able to:
1) Recognize that all waves transfer energy
2) Recognize the relationship between frequency and wavelength to the energy of an electromagnetic
and a mechanical wave
3) Compare and contrast electromagnetic waves to mechanical waves
4) Define and recognize common examples of reflection, refraction, interference and diffraction
5) Relate the speed of sound to the characteristics of different media
6) Predict the Doppler effect of a moving sound source or a moving sound receiver
7) Given common examples of static electricity, explain the flow of electrons in terms of friction,
induction and conduction
8) Define alternating and direct current in terms of the flow of electrons
9) Calculate voltage, given current and resistance
10) Distinguish series circuits from parallel circuits in terms of the flow of electrons
11) Describe how the flow of electrons creates a magnetic field that can be used to produce an
electromagnet
12) Describe how an electromagnet can be used to produce a simple motor
13) Recognize examples of permanent magnets.
Waves and Energy
A wave is a disturbance that transfers energy through matter or through space. Some waves, like sound
waves, must travel through matter while others, like light, can travel through space. Energy is transferred
to nearby particles and they move, causing other particles to move. Energy is transferred from one place
to another. The particles of matter do NOT move along with the wave. ONLY the energy that produces
the wave moves with the wave.
Waves can be compressions of energy (Compression / longitudinal wave) or made up of up and down
movements (Transverse wave). An example of a compression wave is sound. Examples of transverse
waves include water waves and earthquakes.
Parts of a Wave:
A. Amplitude - the height of a wave above or below the midline
B. Crest - the peak or top of the wave
C. Midline (normal) - original position of the medium before the waves move through it.
D. Trough - the lowest point of the wave
E. Wavelength - the distance between two peaks.
Relating Frequency and Wavelength
Frequency is the how fast the wave is moving. If you stand in one spot and watch a wave go by, it is the
number of crests that go by in a second.
Waves with long wavelengths have a low frequency. Waves with short wavelengths have a high
frequency. The higher the frequency, the more energy a wave has. Also, waves with short wavelengths
have more energy than larger wavelengths.
The speed or velocity of a wave depends on the wavelength and the frequency. The formula for wave
speed is:
Speed = wavelength x frequency
Mechanical Waves
Longitudinal versus Transverse Waves
One way to categorize waves is on the basis of the direction of movement of the individual particles of the
medium relative to the direction which the waves travel. Categorizing waves on this basis leads to three
notable categories: transverse waves, longitudinal waves,
and surface waves.
A transverse wave is a wave in which particles of the
medium move in a direction perpendicular to the direction
which the wave moves. Suppose that a slinky is stretched
out in a horizontal direction across the classroom and that a
pulse is introduced into the slinky on the left end by
vibrating the first coil up and down. Energy will begin to be
transported through the slinky from left to right. As the energy is transported from left to right, the
individual coils of the medium will be displaced upwards and downwards. In this case, the particles of the
medium move perpendicular to the direction which the pulse moves. This type of wave is a transverse
wave. Transverse waves are always characterized by particle motion being perpendicular to wave motion.
A longitudinal wave is a wave in which particles of the
medium move in a direction parallel to the direction which the
wave moves. Suppose that a slinky is stretched out in a
horizontal direction across the classroom and that a pulse is
introduced into the slinky on the left end by vibrating the first
coil left and right. Energy will begin to be transported through
the slinky from left to right. As the energy is transported from left to right, the individual coils of the
medium will be displaced leftwards and rightwards. In this case, the particles of the medium move
parallel to the direction which the pulse moves. This type of wave is a longitudinal wave. Longitudinal
waves are always characterized by particle motion being parallel to wave motion.
A sound wave traveling through air is a classic example of a longitudinal wave. As a sound wave moves
from the lips of a speaker to the ear of a listener, particles of air vibrate back and forth in the same
direction and the opposite direction of energy transport.
Each individual particle pushes on its neighboring particle
so as to push it forward. The collision of particle #1 with
its neighbor serves to restore particle #1 to its original
position and displace particle #2 in a forwards direction.
This back and forth motion of particles in the direction of
energy transport creates regions within the medium where the particles are pressed together and other
regions where the particles are spread apart. Longitudinal waves can always be quickly identified by the
presence of such regions. This process continues along the chain of particles until the sound wave reaches
the ear of the listener.
Waves traveling through a solid medium can be either transverse waves or longitudinal waves. Yet waves
traveling through the bulk of a fluid (such as a liquid or a gas) are always longitudinal waves. Transverse
waves require a relatively rigid medium in order to transmit their energy. As one particle begins to move
it must be able to exert a pull on its nearest neighbor.
THE ELECTROMAGNETIC SPECTRUM
The electromagnetic spectrum is a set of electromagnetic waves in order of wavelength and frequency - a
long wavelength has a low frequency, a short wavelength has a high frequency. Electromagnetic waves
can travel through space. They do not need to travel through a medium like air or water, though they can.
The Spectrum in Order
Least
Energy
Radio Waves
TV)
Microwaves
lowest frequency and longest wavelength, used for communication (radio and
Infrared Waves
cannot be seen, felt as heat, “below” red, used for cooking, medicine, night
sight
Visible Light
portion of the spectrum that your eye is sensitive to, consists of seven colors
(ROYGBIV), red has the lowest frequency/energy and violet has the highest
frequency/energy
used in cooking and for RADAR
Ultraviolet Waves present in sunlight, “beyond” violet, energy is enough to kill living cells, used
for sterilization
Most
Energy
X-Rays
energy is enough for photons to pass through the skin, for medicine
Gamma Rays
highest frequency, shortest wavelength, certain radioactive materials emit them,
have tremendous ability to penetrate matter, used in the treatment of cancer
Wave Interactions
When a wave hits a piece of matter, the wave can be absorbed or it can be reflected.
Reflection
 The bouncing back after a wave strikes an object that does NOT absorb the wave’s energy.
 The Law of Reflection states that the angle of the incidence is equal to the angle of reflection. In
other words, the angle that it hits the object at will be the same angle, in the opposite direction,
that the waves leaves the surface
Refraction
 The bending of waves due to a change in speed. This time the wave is absorbed and not reflected.
 Waves move at different speeds in different types of matter. Temperature can also affect the speed of
a wave.
 Examples include prisms (bends white light into its component colors), lenses like glasses and
contacts, and a mirage.
Diffraction
 The bending of waves around a barrier. When it encounters a barrier, the wave can go around it.
 Electromagnetic waves, sound waves, and water waves can all be diffracted. Diffraction is important
in the transfer of radio waves. Longer AM wavelengths are easier to diffract than shorter FM
wavelengths. That is why AM reception is often better than FM reception around tall buildings and
hills.
 Examples include rainbow glasses, diffraction gratings
.
Interference
 The phenomenon which occurs when two waves meet while traveling along the same medium. The
interference of waves causes the medium to take on a shape which results from the net effect of the
two individual waves.
 When two waves’ crests or troughs combine, there is an additive effect – this is called constructive
interference. When one wave’s crest and another’s trough combine, there is a subtractive effect – this
is called destructive interference.
Constructive Interference
Destructive Interference
Sound
Sound moves from its source in the form of compression waves. Sound is a form of energy that causes the
molecules of a medium to vibrate back and forth. Sound cannot travel through space or a vacuum.
Materials that can easily bounce back (elastic) transmit sound easily. Solids are generally more elastic
than liquids or gases because the molecules are not very far away and bounce back quickly. Elasticity
increases the speed of sound. If the objects are in the same phase (ex. both liquids), sound goes slower in
the denser medium. As temperature increases, the speed of sound increases. Sound travels faster at
higher temperatures.
Doppler Effect – Heard an ambulance go by recently? Remember how the siren's pitch changed as the
vehicle raced towards, then away from you? First the pitch became higher, then lower. Originally
discovered by the Austrian mathematician and physicist, Christian Doppler (1803-53), this change in
pitch results from a shift in the frequency of the sound waves, as illustrated in the following picture.
As the ambulance approaches, the sound waves from its siren are compressed towards the observer. The
intervals between waves diminish, which translates into an increase in frequency or pitch. As the
ambulance recedes, the sound waves are stretched relative to the observer, causing the siren's pitch to
decrease. By the change in pitch of the siren, you can determine if the ambulance is coming nearer or
speeding away. If you could measure the rate of change of pitch, you could also estimate the ambulance's
speed
Electricity & Magnetism
Electricity
Static - some of the outer electrons are held very loosely. They can move from one atom to another. An
atom that looses electrons has more positive charges (protons) than negative charges (electrons). It is
positively charged. An atom that gains electrons has more negative than positive particles. It has a
negative charge. A charged atom is called an "ion."
Some materials hold their electrons very tightly. Electrons do not move through them very well. These
things are called insulators. Plastic, cloth, glass and dry air are good insulators. Other materials have some
loosely held electrons, which move through them very easily. These are called conductors. Most metals
are good conductors.
How can we move electrons from one place to another? One very common way is to rub two objects
together. If they are made of different materials, and are both insulators, electrons may be transferred (or
moved) from one to the other. The more rubbing, the more electrons move, and the larger the static charge
that builds up. (Scientists believe that it is not the rubbing or friction that causes electrons to move. It is
simply the contact between two different materials. Rubbing just increases the contact area between
them.)
Static electricity is the imbalance of positive and negative charges.
OPPOSITES ATTRACT
Now, positive and negative charges behave in interesting ways. Did you ever hear the saying that
opposites attract? Well, it's true. Two things with opposite, or different charges (a positive and a negative)
will attract, or pull towards each other. Things with the same charge (two positives or two negatives) will
repel, or push away from each other.
A charged object will also attract something
that is neutral. Think about how you can make
a balloon stick to the wall. 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. (At least until
the electrons on the balloon slowly leak off.) It works the same way for neutral and positively charged
objects.
So what does all this have to do with static shocks? Or static electricity in hair? When you take off your
wool hat, it rubs against your hair. Electrons move from your hair to the hat. A static
charge builds up and now each of the hairs has the same positive charge. Remember,
things with the same charge repel each other. So the hairs try to get as far from each
other as possible. The farthest they can get is by standing up and away from the
others. And that is how static electricity causes a bad hair day!
As you walk across a carpet, electrons move from the rug to you. Now you have extra electrons and a
negative static charge. Touch a door knob and ZAP! The door knob is a conductor. The electrons jump
from you to the knob, and you feel the static shock.
We usually only notice static electricity in the winter when the air is very dry. During the summer, the air
is more humid. The water in the air helps electrons move off you more quickly, so you can not build up as
big a static charge
Current Electricity
To make "something" (refrigerator, light, computer, radio controlled car, sewing machine......) turn on we
need :
 an appropriate source of electricity,
 metal wires insulated with plastic,
 a switch
 and the thing.
We connect them in a distinct sequence for the thing to work.
The source is a source of energy.
- In the case of DC (Direct Current – (battery) current flows in one direction only), it has a limited life
then is unusable so we throw it away.
- In the case of AC (alternating Current – (wall plug) current flows back and forth (changes direction)) the
power company provides the electricity, it is far closer to limitless as an energy source.
The energy is transferred to the globe or CD player where it changes to light or heat or motion or sound all forms of energy. Because the connecting wires are extremely good conductors of electricity, very little
energy is lost as heat in them. The switch merely allows or stops the transfer of energy.
But why is it necessary to have two wires? Surely the transfer can take place with only one wire? The
answer lies in the method of transfer - the motion of electrons from high potential energy in the source to
low potential energy in the source. One wire carries electrons to the globe or CD player from the source,
the other returns them to the source whereupon they are boosted back up to continue their circulation.
In any material, especially conducting material, electrons on the outside of atoms are relatively free to
migrate around the atomic crystal structure which, of course remains in place.
This flow of electrons around the
wires through both the source and CD
player is continuous while the switch is
closed turning on the player. Because it
makes a continuous loop, we call the
arrangement a circuit.
The flow of electrons is called a current,
an electric current. They flow from high
to low energy in response to an electric
field established in the wires and CD
player- a region of influence on charges
by other charges.
You may remember something about
"like charges being repelled". That is precisely what is happening in the circuit, negative electrons are
being repelled from the "negative terminal" of the source and subsequently attracted to the positive
terminal. The source uses energy from some other means to keep the electrons flowing WITHIN the
source from positive to negative - chemical or mechanical energy. This completes the loop.
A crude but useful analogy can be made to a continuous water loop in a modern entertainment park. (Like
the one at Six Flags)
Think of the rafts as electrons, the moving ramp as the battery or mains, the gentle start and finish as the
connecting wires, and the rapid as the CD player where the energy is lost.
The rafts move in a continuous circuit and are responding to the change in gravitation potential energy
given them by the ramp. Most energy is lost in the rapid where the thrills are. The rafts, like the actual
electrons, are merely responding to conditions around them, the energy change, the physical make up of
the surrounding river bed, etc. Electrons respond similarly to things like the material they are moving
through ( crystal structure, surrounding atom types, magnetic fields etc).
Notice -- provided some cantankerous old sod isn't sinking or removing rafts, the number of rafts
passing anyone watching, anywhere, is the same in say, an hour! --- which means that in a real
circuit, the number of electrons entering and leaving the battery in say, a second, is the same. -(think about it.) This is important.
Calculating Voltage
Free electrons tend to move through conductors with some degree of friction, or opposition to motion.
This opposition to motion is more properly called resistance. The amount of current in a circuit depends
on the amount of voltage available to motivate the electrons, and also the amount of resistance in the
circuit to oppose electron flow. Just like voltage, resistance is a quantity relative between two points. For
this reason, the quantities of voltage and resistance are often stated as being "between" or "across" two
points in a circuit.
The formula for calculating voltage is:
V=IxR
Series vs Parallel:
There are 2 ways to connect multiple devices to a power source (e.g. speakers to an amplifier), series and
parallel.
Speakers in series
In a series circuit (like the two above), the current must
flow through one device to get to the next device. This
means that the rate of current flow through all devices is
the same. The voltage across each device depends on its
impedance/resistance of each device and the current
flowing through the circuit. When adding more
components in a series circuit, the current flow
decreases, if the applied voltage remains constant.
Speakers in parallel
In a parallel circuit (like the two examples above), each
device is directly connected to the power source. This
means that each device receives the same voltage. The
amount of current flowing through each device is
dependent on the impedance/resistance of that particular
device. If devices are added to the power source in a
parallel configuration, the current demand/flow from the
power source increases.
In the 2 diagrams below, you can see the relationship between the current flow out of the amplifier and
the number of speakers. You can see that four speakers draws twice as much current from the amplifier
than the two speaker configuration.
Magnetism
Magnetism is a universal force like gravity. A magnet always has two poles - north and south. Like poles
repel each other and opposite poles attract. There is a magnetic field around a magnet and the invisible
lines of force run from one pole to the other.
A permanent magnet is a magnet that is permanent, in contrast to an electromagnet, which only behaves
like a magnet when an electric current is flowing through it. Permanent magnets are made out of
substances like magnetite (Fe3O4), the most magnetic naturally occurring mineral, or neodymium, a
powerfully magnetic synthetic substance. The Earth itself is a huge permanent magnet, though its
magnetic field is quite weak relative to its size. Humans have used the magnetic field of the Earth for
navigation since the compass was invented in ancient China
Even the most powerful permanent magnet is not as strong as the stronger electromagnets, so their
applications are limited, but they still have many uses. The most mundane would be use as refrigerator
magnets, but magnets can be found everywhere, including your hard disk, ATM and credit cards, speakers
and microphones, electric motors, and toys. Electric motors work through an interaction between an
electromagnet and a permanent magnet.
Every permanent magnet generates a magnetic field, just like any other magnet, which circulates around
the magnet is a distinct pattern. The size of the magnetic field is related to the size of the magnet and its
strength. The easiest way to view a magnetic field generated by a permanent magnet is to scatter iron
filings around a bar magnet, which quickly orient themselves along the field lines.
Every permanent magnet has two poles, named north and south, though they could have just as easily
been called A and B. Similar poles repel while opposite poles attract. It takes a lot of effort to hold
repelling poles of a magnet together, while it takes effort to remove attracting poles. The most powerful
magnets attract so hard that they can cause injuries by pinching skin between them.
A magnetic field can be produced using a current through a wire and a piece of metal that can be
magnetized. Electricity and magnetism are related.
Electricity can produce a magnetic field and magnetism can produce an electric current.
Electromagnetism
An electromagnet is a temporary magnet. As long as there is a current flowing, a magnetic field is
present. A simple electromagnet consists of a battery, copper wire, and an iron nail. The strength of the
electromagnet depends on the number of turns in the wire coil and the size of the iron core. The greater
the number of turns, the stronger the magnetic field that is produced.
Magnets are used in electric motors. An electric motor is a device that produces a direct current. It
contains an electromagnet, a permanent magnet, and a commutator. The electromagnet is placed between
the poles of the permanent magnet. The poles repel and attract each other and the electromagnet spins.
Electric energy is converted into mechanical energy. This is the opposite of a generator.
Magnets are also used in television sets. The Non-plasma televisions all have a cathode ray that uses
electrons and fluorescent materials to produce images on a screen. An electromagnet changes the path of
the beam of electrons which allows it to sweep the television screen many times a second.
Electromagnet
You can increase the strength of an
electromagnet by increasing the current
flowing through the wire or by increasing
the number of coils.
Name _________________________________________________________Date ________period_____
Physical Science EOCT Review
Physics – Waves, Electricity, and Magnetism
1. The amplitude of a wave can be measured from the (medium, crest) or the (trough, wavelength) to
the rest position of the wave’s medium.
2. The wavelength of a transverse wave is often measured from (crest to crest, crest to trough).
3. The number of waves that pass a point in one (second, minute) is the wave’s
(amplitude, frequency).
4. Waves with longer wavelengths have a (lower, higher) frequency and waves with shorter wavelengths have a (lower,
higher) frequency.
5. A wave that has a high frequency will have (high / low) energy
6. What happens to the speed of light as it enters a different medium?
7. What color of the visible light portion of the spectrum has the highest frequency and highest energy?
Which color has the lowest frequency and energy?
8. First, label each diagram as either transverse or longitudinal (compressional) then label the parts of each wave.
9. Label whether the following examples are reflections, refractions, diffractions or interference.
A)
B) A rainbow
C) looking at yourself in a mirror
D)
E)
10. Sound travels faster through ________________(solids, liquids or gases). Why?
11. Give two examples of the Doppler effect in everyday life.
12. What is the difference between direct current and alternating current
13. What is the potential difference across a resistor that dissipates 5.00 W of power and has a current of 5.0 A
14. A 13  resistor has 0.050 A of current in it. What is the potential difference across the resistor?
15. Tell whether the following circuits are series or parallel.
16. Draw lines to show the magnetic field between the two magnets below.
17. Label the parts of the electromagnet.
18. What happens when the number of coils of an electromagnet is increased?