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Physics revision

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balaji saravanan

on 28 October 2014

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Transcript of Physics revision

IGCSE Physics revision
Physics
Basics

Properties of waves and sound including light
Electricity and magnetism
Atomic physic
Thermal physics
General Physics
Speed, velocity and acceleration
Mass and weight
Density
Forces
Energy, work and power
Simple kinetic molecular model of matter
Thermal properties
Transfer of thermal energy
General wave properties
Light
Sound
Simple phenomena and magnetism
Electrical quantities
Electric circuits
Dangers of electricity
Electromagnetic effects
Cathode - ray oscilloscope
Radioactivity
The nuclear atom
Makes the
measurements
more
precise
Get
average

for
more
accurate

measurements
Take

multiple
times to get more
reliable

measurements
Better results :
Equations:
Speed
:
Scalar
quantity
Is the
measure
of
how much distance
an
object can travel in a set unit of time
Eg. a car is traveling at 150km/h
Velocity
:
Vector
quantity
Eg. a car is traveling south at 200km/h
Distance-Time Graph
1.
2.
3.
4.
1. Graph shows an
increasing gradient
which means that the car is
accelerating
. This means that the car is
traveling further each second

than before.
2. The curve earlier
straightens out
meaning that the car has
stopped accelerating
and is keeping a
constant

speed
.
3. Graph shows a
decreasing gradient
which in turn shows that the
car is
decelerating
4. When the curve becomes
flat
it shows that the
distance stays the same
which in turn shows the
car has

stopped
.
On a
distance-time
graph, the
gradient
is numerically
equal to
the
speed
Speed-time graphs
On a speed-time graph the
gradient

equals
the
acceleration
Area

under
the
graph

equals
to the
distance
travelled
Explanation :
Gradient:
Acceleration:
The
change
in
velocity
/speed
per

second
Free fall:
If a
feather

and
a lead
ball
were dropped both
will fall at same speed
-
if
there was
no

air resistance
An object falls due to gravity
The speed at which it would fall after it has reached
terminal velocity
is 120 m/s2
- this is because the
gravity

near
the
earths
surface is
10 m/s2 (newtons)
Terminal velocity
-
Once air resistance
is
equal to
the force of
gravity,
the

object has reached terminal velocity
. This
means
that it will stay at a
constant

velocity
/speed.
Measuring G's :

Mass:
The
measure
of
how much matter
is in an object
The mass
shows
the
objects resistance to change in motion
(
inertia
)

Weight:
Is the
effect

of gravitational field on
the
mass
of an object
Weights
can
be
compared
using a
balance
(therefore masses can be compared to)
To determine the density:
1.
Find
the
mass
using a weighing scale
2.
Find
the
volume

Using a
eureka

can
and measuring the amount of
water displaced = volume
Can also use a
measuring cylinder
and measure the
increase in water level
Relative density is used to compare the density of water to other substances
Effects of forces
Force
may
produce
:
A
change
in
shape
A change in
size
Extension of a spring:

Steps:
1.
Measure
the
spring without
a
load
2.
Add
a
mass
and measure the
distance stretched
3.
Add more
weights
until elastic limit
has been reached
4.
Plot
the
graph
of extension using -
Beyond
the
elastic limit
the
spring
is
permanently stretched

Before
the
elastic limit
the
spring

returns
to it's
original position

After
elastic limit
extensions
are
larger

for
the
same

increase
in
force
extension = y - axis
force = x - axis
Hooke's law:
The
extension directly proportional
to the
applied force
,
provided
the
elastic limit
is
not exceeded
After elastic limit =
limit of proportionality
:
Where the
extension
is
no
more
directly proportional to
the
load
Newtons 1st law of motion
:
If no external force
is
acting
on it, an
object
will:
If stationary remain stationary
if moving, keep moving
in
a
straight line
, at a
constant speed
Resultant force:
Resultant force:
Net
overall force on an object including
size
and
direction
Explanation:
Force can cause a change in direction
Here the object moves in a circle because :
the
force
is acting
perpendicular
(
at a right angle
) to the
direction of travel
The
force constantly changes the direction
of the object therefore;
velocity changes but speed stays constant

(object accelerates towards center of circle)
Centripetal force:
The force that makes an object move in a circle

Force increases if
:
Mass
of object
increases
Speed
of object
increases
Radius
of circle
decreases

If
the centripetal
force
was suddenly
removed
the
object
will
move
at a
tangent to the circle
Time taken
to do

one swing
is
called
period
How to improve accuracy of period:
Use a
Digital stopwatch
Measure

20-100 oscillations
(
swings
) and then
divide
by the
total time taken
Repeat
this several times to
get
an
average
Check
that the
stopwatch
has been
set to zero
Turning effect
Amplitude

of
the
oscillation
:
Distance between
the
highest points
of the weights
How to find the amplitude:
1.
Use
a
protractor
and a
ruler

2.
Measure
the value of
max angle
and the
distance

from
the
vertical
(center - when weight at rest)
A
turning effect of a force
is called a
moment
(torque)
Moments are split into :
Equilibrium-
The
sum of
the
clockwise
moment
about the pivot

equals
to the sum of
anti-clockwise
moment
If
a beam is in
equilibrium
there is
no resultant moments
There is
only
a
net force
(above total = 30N)
Center of mass
Example:
Finding the
center of mass of a plane
:
1.Get a
stand
and make a
weighted plumb line
2.
Punch
a
minimum of 2
holes
on the plane
3.
Hang
your
plane

from
the
hole
4.
Draw
the
plumb line

on
the
plane
5.
Repeat
with other holes. Then
where
the
lines

intersect
(meet)
is
the
center
of mass
Center of mass
= is an
imaginary

point

in
an
object

where
the
total mass
of the object can be thought to be
concentrated

States of Stability:
A) Here the center of mass is over a very large base so the object will have to be tilted very far to make the turning effect great enough to topple it
B) Here the center of pressure (base)
is very small so only a small force is
needed to make center of mass go over
the base
(c) neutral
C) here the center of mass is always above the center of pressure - so it can never be toppled
For

stability
the
center of mass
must be
over
the
center of pressure
Finding vectors:
Finding vector: drawing scale diagrams
Here instead of aligning the lines you are just using the
parallelogram rule
:
Which means you are
drawing parallel lines to form 2 triangles
instead of one
Only works if the arrows follow on
An
object
may
have energy because
of its
movement
(
kinetic
energy) or because of its
position
.
Energy can

be transferred

from one type to another
and
stored
.
Law of conservation
:
Energy cannot be

made
or
destroyed
. It can
only
be
transferred
from one form to another
Energy
Energy calculations:
(Vertical height)
Energy resources
Renewable
energy: Energy that
can
be
replenished
Non-renewable
energy: Once used the energy
cannot be replaced

Nuclear fission vs fusion:
Nuclear
fission
:
In the
nuclear power plant
Breakdown of U-235
Nuclear
fusion
:
Only in the
sun
Hydrogen

nuclei are pushed

together

to

make helium = energy release
Efficiency:
The
ratio
of
useful work done to
the
energy supplied
to it

eg. Car engine loses a lot as heat but equally provides thrust
Work
Work done
= the
magnitude
of a
force
and
distance moved
(Force needed to make and object move)
Work done = Energy transformed

(eg. If a brick falls it loses 20J of potential energy,
this is changes into 20J of kinetic energy. So 20J of work is done in accelerating the brick)
1 joule

of work is done

when
a force of
1 newton moves
an
object 1 meter
in the direction of the force
Power
Power
=
Work done per second
or
energy transformed per second
Pressure
Pressure increases when:
Force applied increases
Area of contact decreases
Barometer
: Used to
measure atmospheric pressure
The
atmospheric pressure
of the air
pushes
down
on
the
reservoir
,
forcing
the
mercury up
the tube
and compressing
the
vacuum
760mm = 1atm (pressure)
reservoir
This above formula can also be used to find out the pressure of any other liquid such as the sea
Pressure
in a
liquid
:
increases with depth
increases with density
gas supply
Manometer
: Used to
measure

pressure of specific gas
The
height difference = excess pressure
due to the gas
Solid
Liquid
Gas
Particles are :
Closely packed together
Arrangement :
Regular
( Lattice )
Movement :
Vibrate constantly in fixed position
Force :
Strong

Shape :
Fixed

(Can't be compressed)
Particles are :
Close together

Arrangement :
Irregular
Movement :
Move around and slide past each other
Force :
Weak
Shape :
Takes shape of container

(Can't be compressed)
Particles are :
Far apart
Arrangement :
Random
Movement :
Able to move freely and collide with other particles and bounce away
(can spread)
Force :
No force
Shape :
Fills container

(Can be compressed)
Brownian motion
(diffusion)
The
random movement of particles
suspended in a liquid or gas
,
caused by collisions with molecules of the surrounding medium
. Also called Brownian movement.
States of matter:
•The
hotter
the
particle
is the
faster it moves
and the
more kinetic energy
they have
•The
pressure
gases exert on a container is
due to
the
particles colliding on
the
container walls

If
the
volume
is
constant
, then
increasing
the
temperature
will
increase
the
pressure

Evaporation
Pressure changes
Evaporation vs boiling
Is the
escape

of

more
energetic molecules

from
the
surface
of a liquid
Evaporation can be accelerated by:
Increasing

temp
erature
Increasing

surface area

Increasing
the
air

that
is
blown

over
the
surface

Reducing
the
humidity
level
Cooling effect of evaporation:
As
the
molecules

leaves
the
surface
they
take some heat energy

from
the
surrounding
with them
therefore

cooling
the
surrounding
This means for e.g. sweat takes the heat from our skin and then evaporates with that energy
cooling our body
For a fixed volume of gas
Decreasing volume increases collisions which increases pressure
or

Like

poles

repel
and
unlike poles attract
Opposites attract
Induced magnetism
:
Material
such as iron and steel are
attracted to magnets
As

they
themselves
are magnetized
this is known as induced magnetism
North pole
=
north seeking pole
(is
attracted to
the
earths north pole
)
Why the iron nail is magnetized:
When
the
magnet
is
brought near
the
iron
The
domains
in the
iron

line-up with the north pole of
the
magnet
Domains -
imagine them as tiny magnets
So
because
the
iron
is
magnetized
, the
iron
is
attracted to magnet
The line - up of the domains = (To get right poles in a question ) The rule is the
ferrous metal
is
always attracted to
the
magnet
and
in order for the metal to be attracted, the poles have to be opposite
Methods of Magnetisation:
Inducing magnetism produces a weak magnet. It can be magnetised strongly by
stroking with one end of a magnet, in one direction
the
most effective method
is to
place the metal in
a
long coil of wire
(
solenoid
) and
pass a large DC
(
direct current
) through the coil.
Methods of demagnetisation:
By
physical force
such as -
smashing
it with a hammer, or
dropping
it
By
heating
it










solenoid
method but
with alternating current
ferrous
:
magnetic
– anything which contains iron, nickel, or cobalt can be magnetised
Non - ferous
:
non-magnetic
e.g. copper, grass,
ketchup(wow must include food)
,
butter
, wood etc.


The magnetic field lines of a bar magnet
Out of the north and into the south
Experiment to find the field lines:
We can detect them using
iron filings
. The tiny pieces of
iron line up in a magnetic field
.
Iron vs Steel:
Iron
Is an
element
Forms a
temporary magnet
(soft magnetic material)
-
will lose
it's
induced magnetism
after a while
Steel
Is an
alloy
(
iron + carbon
)
Forms a
permanent magnet
(hard magnetic material)

-
will retain
it's
induced magnetism
Electromagnet:
When a
current flows through
a
coil
of wire, a
magnetic field
is
created
The
field line of
the
coil
are
identical

to
the
bar magnet
An electromagnet uses this principle to become a
magnet that can be turned ON/OFF
It
can be switched off because
it has a
soft magnetic core loses it's magnetism
after the magnetism from the coil stops - It is
switched OFF by stopping the current
through the wire
Strength
can be
increased

by
:
increasing voltage
supplied to the coil
Uses:
As a
relay
( explained later)
In
electric motors
( explained later )
Used in
cranes

that need magnets
to lift heavy magnetic objects or
sorting

ferrous

material

and non-ferrous
Magnetic storage
Production

of electrostatic charges
:
Usually the
electrons from
another
object
is
transferred onto
the
object
that is
being

charged
Best way, is by using a van der graph generator
The sparks that come out is caused by the attraction of the positive charge to the negative charge
Rubbing
a rod with a cloth
Rubbing your hair against the balloon

Detection

of electrostatic charges
:
physical movement
The biggest give away is the sparks
Also if 2 charged rods are placed next to each other they may repel or be attracted to one another
If a charged rod is placed next to a stream of water the water stream will bend towards the rod
Small pieces of paper jumping towards rod
Can also use the leaf electroscope
Electrostatic charge
:
An object can be charged negatively or positively
There is a
positive (+) charge (
carried by
proton)
There is a
negative (-) charge (
carried by
electron)
Like charges repel
and
unlike attract
(just like magnet)
+ and + repel
+ and - attract
Charge measured in

coulombs ( C )
Charging by induction
:
The process of giving an object a charge = charging
A) The negatively charged
rod repels the negative charges
in the sphere, leaving the positive charges behind (
positive charges do not move
)
B) The
grounding wire allows the electron to flow
off the sphere and
into the ground
(the
sphere
has been
earthed
)
C) The rod no more attracts the positive charges, therefore the
positive charges are distributed evenly
. Leaving the
sphere positively charged

Conductors and insulators:
Conductor
-
substances

that

allow electricity to pass
through them
Metals
are best conductors as they have
free moving electrons
Insulator
- substances that
do not allow
electricity to pass
The
electrons are tightly held to atoms
and hardly move, but they
can be transferred by rubbing

Can test whether they are conductors by putting them into a circuit
Uses :
5s
100m
speed
For example, a car accelerates in
5s
from
25m/s
to
35m/s.
Its velocity changes by
35 - 25 = 10m/s.
So its acceleration is
10 ÷ 5 = 2m/s2.
such copy
much paste
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