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Physics
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Physics
Review
9-12 Science Std: Phys 3, 4, 5
Topic: The Right Tool
You must choose the right
equipment to get the best
scientific readings
To record sounds you would
use a microphone
To measure earthquake energy
you would use a seismograph
To measure electrical charge,
current or voltage you would
use a Electrometer, ammeter or
Voltmeter
To measure temperature you would
use a thermometer
Std I&E 1a
Topic: The Right Tool
Once you have your readings,
you need to organize and
compare your readings
You can start by putting the
data into a table
You can take the data from the
table and put it in a spreadsheet
And once you put it into the
spreadsheet, you can look at
the data on a graph
Std I&E 1a
Topic: Entropy*
Entropy is a physics term that
describes:
The amount of disorder is in a
system
Low Entropy means something is
very organized, clean and
everything is behaving nicely
High Entropy means something
is disorganized, messy and
everything is behaving badly
It is a fact that Entropy is
always increasing
And things will move to a
less orderly state
Std 3f
Topic: Wave Types
Waves have 2 different shapes
The first type is a transverse
wave
EM Waves are transverse waves
We made transverse waves
when we were shaking a slinky
The second type is a
longitudinal wave
Sound waves are
longitudinal waves
Std 4b
Topic: Wave Motion
As a wave moves through
something it makes parts of
the material move
As a transverse wave moves
by:
It makes the material (or
anything that is on it)
move up and down
Watch the little black dot as
the transverse wave goes
past it
If you were on a surf board on
the ocean
The transverse wave would
make you move up and
down
Std 4a
Topic: Sound Waves
Sound waves are longitudinal waves
Sound waves need a material (medium) to travel through
Sound waves move through the medium by
having molecules bump into each other
When the molecules bump into each other, they transfer
the wave energy from one molecule to the next in a
direction parallel to the direction of the sound
Std 4b
Topic: Speed of Sound
Several things affect the speed
of sound in materials
Temperature: Higher
temperature = sound moves
faster
Sound moves faster in the
desert heat than the artic cold
Density: Higher density = sound
moves faster
Sound moves faster in water or
steel than in air
Flexibility: Lower flexibility =
sound moves faster
Sound moves faster in a stiff plastic
pole than a soft plastic toy
Std 4d
Topic: EM Wave Spectrum
Electromagnetic Waves are a
special kind of wave
Depending on the frequency
(and the wavelength) of the
wave, we have special
names for the waves
Some of the special names are
radio waves, microwaves,
ultraviolet waves, x-rays and All of these waves are
transverse waves and
visible light
can move without going
through a material
(medium)
Std 4e
Topic: EM Wave Speed
Electromagnetic waves are
special for many reasons
They travel faster than
anything else known today
In a vacuum (out in space) they
all travel at the same speed
They go at the speed of light
And the speed of light is:
3 x 108 meters per second
Std 4e
Topic: Refraction
Refraction is a bending of
waves caused by a change
in the speed of the wave
This can be caused by either:
Going from one material into
another material with a
different wave speed
Or a change in the material
that causes a change in
the speed of the wave
Std 4f
Topic: Index of Refraction
You can measure how much a
wave will bend using the
Index of Refraction (n)
The Index of Refraction is a
measure of how much the
velocity changes in a
medium
For light, the Index of Refraction
is the speed of light in a
vacuum (c) divided by the
speed of light in the material
(v)
The bigger the Index of
Refraction, the slower
the wave speed in the
material
Std 4e
Topic: Index of Refraction
If you compare the Index of
Refraction for 2 materials…
You can tell how much the
wave is going to bend
If the indices of refraction are
similar (numbers are close to
each other) the wave will bend
a little
If the indices of refraction are
not similar (numbers are
far apart) the wave will
bend a lot
Std 4f
Topic: Doppler Effect
The Doppler Effect is an apparent
change in the frequency of a wave
The change is caused by
relative motion between the
source and the observer
If a sound wave is coming
towards the listener, the pitch
goes up
If the sound is going away from
the listener, the pitch goes
The bigger the difference in
down
speed between the sound
If the sound is not getting closer
and the listener, the
or farther away from the
bigger the change in pitch
listener, the pitch doesn’t
change
Std 4f
Topic: Sound Beats
When sound waves add together
it is called interference
If two sound frequencies are
close together, when they
add you hear sound beats
The number of beats you hear
depends on the difference in the
sound frequencies
The smaller the difference, the
smaller the beat frequency
The larger the difference, the
larger the beat frequency
If there is no difference,
you don’t hear any beats
Std 4f
Topic: Sound Limits
We know that sound is a
longitudinal wave
And that all waves (except for EM
waves) need to travel through
something (a medium)
So sound waves need a
medium to travel through
(air, water, etc.)
If you don’t have a medium,
sound waves can’t travel
That is why sound won’t
travel in a vacuum (in a
place without any air)
And in space, no one can
hear you scream……
Std 4f
Topic: Wave Energy
All waves transfer energy when
they move
Some waves need a medium to
move, some don’t
If a wave needs a medium, the
medium ends up in the same
place where it started after the
wave goes past
We saw this when we did
the lab with the string
telephones
The sound waves moved
through the string but it
didn’t move the string Std 4a
Topic: Wave Energy
So what happens to this energy?
Sound waves can cause things
to move
And when things move they rub
against each other
When they rub against each
other, friction causes them to
heat up
So if you had a loud
enough sound wave,
you could heat up
water!
Std 4d
Topic: Electrostatic Force
Electrically charged particles
can be either positive (+) or
negative (-)
Charged particles can push or
pull on each other (force)
The amount of force depends on
2 things:
The amount of charge (+) or (-)
– more charge = more force
The distance between the charges
– more distance = less force
If the distance gets big enough, the force goes to 0 (goes away)
Std 5e
Topic: Electrostatic Force
When you have 2 charges,
they can either pull or push
on each other
If the charges are the same
(alike) they push against
each other
If the charges are opposite
(different) they pull towards
each other
So remember that opposites
attract and alike repel
Std 5e
Topic: Electrostatic Force
When we draw Electrostatic
Forces, we show the amount of
force a special way
If we draw a small number of
lines we have a small force
If we draw more lines we have a
bigger force
If we draw many lines we have
a big force
So more lines = more force
And the closer the lines are to each
other = the stronger the force is
Std 5m
Topic: Electrostatic Force
How much does the force
change?
This is the equation
for the amount of
force between
charges
The amount of charge = q The distance between the charges = r
2x the charge = 2x the force 2x the distance = 1/4x the force
3x the charge = 3x the force
3x the distance = 1/9x the force
A change in the distance between the charges has more
affect because the distance is squared in this equation
Std 5e
Topic: Right Hand Rule
When an electric current goes
through a wire
It makes a magnetic field
around the wire
The direction of the field depends
on the Right Hand Rule
Wrap your right hand around the
wire
Point your thumb in the
direction of the current
Your fingers wrap in the
direction of the magnetic
field
You can see this if you put a
compass next to the wire
Std 5h
Topic: Magnetic Induction
When you move a magnet next
to a wire…
The magnet will induce (or
make) a voltage in the wire
When you have a voltage in
a wire that is part of a
electric circuit…
Electric current will flow
through the circuit
So if you move a magnet next
to wires in an electric
circuit, you will cause
electric current to flow
Std 5h
Topic: Transistors
When transistors were
invented in the 1940’s
They made many changes in
electronics
They could be made cheaper
They could be made smaller
And they used less energy
With all these changes they
quickly replaced bigger
vacuum tubes
Std 5d
Topic: Transistors
Transistors are designed to do
2 things….
The 1st is to be a switch to
turn on and off current
The first function is used
in a computer
The 2nd is to add energy to a
weak input signal
The second function is used
in an amplifier
Std 5d
Topic: Transistors
Transistors have changed
modern electronics
because:
They can amplify small inputs
into larger output signals
They don’t break easily like old
vacuum tubes
They are smaller than vacuum
tubes
So – the computers, radios and cell phones we
use today are much smaller and tougher
Std 5d
Topic: Plasma
Plasma is the 4th state of
matter (solid, liquid, gas…)
It happens when you take a gas and
either heat it to a very hot
temperature or put a large
voltage on it
You can find plasmas in the sun (very hot) or in a
fluorescent light bulb (large voltage)
A plasma is atoms of gas that have had their
electrons pulled off so they are made of Plasma is like a
positive ions and free electrons
gas, but a gas
Because they have ions and
can’t conduct
electrons they are good
electricity
electric conductors
Std 5i