P3 powerpoint frog

KEYWORDS: electromagnet, crane,
Circuit breaker, electric bell, relay
Understand the uses of
electromagnets
ALL – State how to make
an electromagnet
MOST – Describe the
uses of electromagnets
SOME – Evaluate the
uses of electromagnets
Starter
Make a mind map about
everything you remember
about magnets and
electromagnets

Electromagnets
Electromagnets differ from normal magnets in one major way!
They are made by passing an electric current through a wire
that has been wrapped around iron. The current creates a
magnetic field and magnetises the iron core. When the current
is turned off the iron loses its magnetism
LO: Understand the uses of electromagnets

Practical – Electromagnetic strength
1. Increasing the number of coils on an electromagnet
will increase the strength of an electromagnet
2. Certain cores will make an electromagnet stronger
than others
3. Increasing the voltage of the connecting
battery/current passing through the wire will
increase the strength of an electromagnet

Electric bell

Circuit breaker

Electrical relay

Scrapyard crane

KEYWORDS: Fleming’s left hand rule
Understand how
electromagnets can be
used to make things
move
ALL – State how
electromagnets can be
used in motors
MOST – Use Fleming’s
left hand rule
SOME – Explain how
loudspeakers work

The Motor Effect
If a wire carrying a current is
placed into a magnetic field, an
interesting thing happens.
As part of the GCSE course, you
are required to know which
way a wire placed into a
magnetic field moves
LO: Understand how electromagnets can be used to make things move

Fleming’s left hand rule

Electric Motor
An electric motor uses
the motor effect of
electromagnets to create
motion.
• The force on one side
of the wire causes it to
move up
• The force on the other
side of the wire causes
it to move down
• The motor rotates!

Electric Motor
Graphite ‘brushes’ are
used to connect the split-
ring to the battery. This is
used because:
• Graphite is an
excellent conductor
• It causes very little
friction on the
conducting ring

The Loudspeaker

KEYWORDS: Electromagnetic induction,
Generator, coil, wire, magnet
Understand how
generators create
electricity
ALL – State how
electricity can be
created
MOST – Describe how
electromagnetic
induction can be
increased
SOME – Explain
generators work in
detail

Electromagnetic induction
By moving the magnet within the coil of
wire, current can be induced within the
current. Note, that the current is only
induced when the magnet or coil is
moving!
How can the amount of current induced
be increased?
• Increase the number of coils
• Increase the speed at which the
magnet/coil moves
• Increase the strength of the magnet
LO: Understand how generators create electricity

Electric generators
LO: Understand how generators create electricity

KEYWORDS: transformer, core, step up,
Step down, primary, secondary, induced
Understand how
transformers work
ALL – State the function
of step up and step
down transformers
MOST – Explain how
transformers work and
perform transformer
calculations
SOME – Explain why
values from equations
are just an
approximation

Step-up and Step-down
Transformers are an essential
part of the national grid. They
help to increase the voltage
after the power station and
help to decrease it again
when it gets to your house.
LO: Understand how transformers work

How do transformers work?
Discuss with the people on
your pod how transformers
work. Remember the
following:
• The only work with an a.c.
current
• They need to have an iron
core
• They use electromagnetic
induction to work

How transformers work
1. The alternating current in the primary coil makes the iron
core into an electromagnetic
2. As the current is alternating, the magnetic field ‘moves’
and also changes direction
3. This ‘moving’ magnetic field causes a current to be
induced in the secondary coil
4. If the number of coils on the secondary is higher, the
potential difference will increase and it is a step-up
transformer
5. If the number of coils on the secondary is lower, the
potential difference will decrease and it is a step-down
transformer

Transformer calculations
The following equation links together the voltage and
number of coils in a transformer:
𝑉𝑝
𝑉𝑠
=
𝑛 𝑝
𝑛 𝑠
Vp = Voltage on primary coil (v)
Vs = Voltage on secondary coil (v)
np = number of turns on primary coil
ns = number of turns on secondary coil

Transformer efficiency
Transformers are usually about 98% efficient. We can
round this up and say that this is approximately 100%.
Therefore, whatever power the device uses, it will output
the same amount of power!
Power in = Power out

Transformer efficiency
Power in = Power out
Vp x Ip = Vs x Is
Vp = Voltage on primary coil (v)
Vs = Voltage on secondary coil (v)
Ip = Current on primary coil (A)
Is = Current on secondary coil (A)

KEYWORDS: x-ray, CT scanner, Ultrasound
Understand how
physics can be applied
to medicine
ALL – State some
medical applications of
physics
MOST – Describe how x-
rays, CT scanners and
ultrasound work
use of these devices in
particular situations
Starter
Recap questions

Further notes on Ultrasound
Besides using ultrasound to create
pictures of babies, they can also be used
to treat kidney stones!
Kidney stones are small lumps that can
form in the kidneys. They are formed
when small crystals of waste products
filtered by the kidneys build up. When
they are formed, your body will try to
pass them out through the urine.
However, they can sometimes get stuck
in this process and cause immense pain!
LO: Understand how physics can be applied to medicine

Further notes on Ultrasound
Ultrasound can be used to treat kidney
stones. Ultrasound is usually very high
frequency (>20000Hz) outside of the
range of human hearing. If it is directed
at the kidney stones, the high frequency
sound can break them up into smaller
pieces and make it easier for them to
pass out through the urine!

Distance between interfaces
The distance to an object can be found using information from
an ultrasound. It can be found using the following equation:
S = V x T
S = Distance (m)
V = Velocity of sound (m/s)
T = Time (s)

KEYWORDS: refraction, angle of incidence,
Angle of refraction, refractive index
Understand the
phenomena of
refraction
ALL – Describe what
happens during
refraction
MOST – Explain why
refraction occurs
SOME – State the
relationship between
the angle of incidence
and the angle of
refraction
Starter
Refraction mind
map

Refraction
Refraction occurs when light moves
between two mediums that have a
different density. (The word medium
just means ‘something that you can
travel through’)
When light moves into a medium with
a higher density, it slows down and
will bend towards the normal. When
it moves into a less dense medium, it
speeds up and bends away from the
normal.
LO: Understand the phenomena of refraction

Conclusion: Refraction
What can you conclude about the relationship between the
two angles in refraction?
Sin of the angle of incidence divided by Sin of the angle of
refraction will always be a constant. The value of the constant
will change depending on what materials are being used to do
refraction (i.e. refraction with air and glass will have a
different value to air and water and air an oil etc.)

Refractive Index
The refractive index of a material is a measure of
how much light is refracted by it when it passes
through the material. It can be calculated by using
the equation:
Refractive index = Sin I / Sin R
I = angle of incidence
R = angle of refraction

KEYWORDS: refraction, angle of incidence,
Angle of refraction, refractive index
Understand how total
internal reflection
occurs
ALL – Describe total
internal reflection
MOST – Perform
calculations for the
critical angle of an
object
SOME – Explain how TIR
is utilised through
endoscopes and optical
fibres

Demonstration: Critical Angle
When performing
refraction with a semi-
circular block, an
interesting phenomena is
observed. When the light
leaves the block, it bends
away from the normal. This
is expected as it is moving
from a more dense to a
less dense medium.

As we continue to increase
the angle of incidence, we
reach a point where the
refracted light seems to
run across the top of the
glass block! The angle at
which this happens is
called the ‘critical angle’

If we increase the angle
even more, we can see that
the light ray is no longer
refracted. Instead, it seems
to reflect off inside of the
straight edge of the semi-
circular block. This is
known as total internal
reflection
We will explore this in
greater detail later

Critical Angle
The critical angle of a material can be found using
the following formula:
Refractive index = 1/sin(C)
Refractive index = property of a material
C = Critical angle

Uses of Total Internal Reflection
Fibre optic cables are able to
work using total internal
reflection. Light is sent through
one end in short bursts and will
light up the other end.
These fibre optic cables are now
used in high speed internet!
They are now also used in
medicine…

Uses of Total Internal Reflection
Total internal reflection is put to
good use in Endoscopes. These
are cameras that can be used to
look inside patients without
having to perform invasive
surgery.
Light is shone into one end,
travels through the endoscope,
shines off the inside of a patient,
back along the endoscope and
forms a picture!

KEYWORDS: converging, diverging, lenses,
Focal point, virtual, real
Understand how to
draw ray diagrams for
lenses
ALL – state the
definition of converging
and diverging
MOST – Draw ray
diagrams for lenses
SOME – Explain when
virtual and real images
are formed when using
lenses
Starter
Make a mind map of
all the objects that
you can think of that
use lenses!

Converging lens
LO: understand how to draw ray diagrams for lenses
A converging lens is always
convex. It makes rays that are
coming in that are parallel
converge onto a point. The
point where the rays
converge is called the
principal focus, or focal
point.
Converging lenses are used in
magnifying glasses and in
cameras.

Diverging lens
A diverging lens is always
concave. It makes rays that
are coming in that are parallel
diverge. The point where the
rays seem to diverge from is
called the principal focus, or
focal point.
Diverging lenses are used to
correct short sight

Focal length
For both lenses, the distance
between the centre of the
lens and the focal point is
called the focal length.

Real image
When an object is really far
away from a converging lens,
the light rays will be (almost)
parallel when they reach the
lens. The image that will be
formed will be at the focal
length.
We call this image a real
image.

Real image
A real image is an image that
is formed by a converging
lens if the object is further
away than the principal
focus.
The real image will always be
smaller than the actual
object, inverted and forms
after the lens.

Virtual image
When the object is close to a lens, the image that is
formed will be much larger than the actual size of the
object.
We call this image a virtual image.

Virtual image
A virtual image is formed by a converging lens if the
object is nearer to the lens than the focal length. A
diverging lens will ALWAYS form a virtual image. The
image is always bigger than the object, the right way up
and forms before the lens.

Magnification
The magnification produced by a lens can be worked out
using the following formula
Magnification = image height
object height

Formation of a real image by a converging lens
As part of P3, you are required to know how to draw ray
diagrams like the one below to show
Although they look very complicated, they are quite easy
to draw once you know how

Formation of a real image by a converging lens
Drawing ray diagrams for a converging lens is done in 4 easy
steps:
1) Draw the principal axis and the lens (always shown as a
line with arrowheads)
2) Draw the object (drawn as a vertical arrow going upwards
3) Draw a line parallel to the principal axis that refracts at the
lens and goes through the focal point
4) Draw a line straight through the principal axis and the lens
line
5) Draw a line that goes through the focal point and refracts
to become parallel at the lens
6) Draw the object on the other side of the lens where the
three construction lines all join up

Uses of Converging lenses
This final example shows how a
converging lens can be used as a
magnifying glass. When an object
is placed close to the magnifying
glass (closer than the focal
length), the object will appear
bigger than the actual object. The
image formed is virtual
(remember the definition!) and
will also be the right way up (i.e.
not inverted)

Old Skool uses of converging lenses
All cameras have a converging lens. This focuses the light from
distant objects onto a film at the back of the camera. When the
shutter is opened, the film is exposed and a negative is made.
The negative can then be developed into the actual picture!

New Skool uses of converging lenses
Newer digital cameras work in the same way. However, instead of
photographic film at the back of the camera, they have a CCD
imager. When the shutter is opened, the CCD is exposed to light
and it forms the image.

New Skool uses of converging lenses
When an object is placed too close to a camera, it will appear
fuzzy. This is because the object is closer to the lens than the
focal length and the lens is not able to focus the image properly
onto the CCD.

KEYWORDS: converging, diverging, lenses,
Focal point, virtual, real
Understand the
structure of the eye
ALL – label the different
parts of the eye
MOST – Describe what
different parts of the
eye do
converging and
diverging lenses can be
used to correct for
vision problems

How the eye works
Regardless of if you are
looking at an object very
close to you or very far
away, your eye is able to
focus and you are able to
see the object clearly. How
is your eye able to refocus
based on where the object
is?
LO: understand the structure of the eye

How the eye works
1. When light enters the eye, the
ciliary muscles change the
thickness of the lens
2. The light is focused by your
lens onto the retina
3. The light sensitive cells in the
retina send electrical impulses
through the optic nerve to
your brain
4. Your brain processes these
impulses and shows you what
the object looks like
What happens if
too much light
suddenly enters
the eye?

Correcting vision
By using our
understanding of how
the eye works and how
lenses work, we can
design glasses to correct
for sight problems

Short sight
In a normal eye, the lens focuses
the image exactly on the retina.
However, in the eye of a person
with Myopia (short sighted), the
image is formed before the retina.
This leads to a blurred image.

Correcting short sight
Short sight can be corrected by
glasses that have a concave
(diverging) lens. This causes the
light rays to diffract outwards
slightly as they pass the lens so
that they are focused exactly on
the retina by the lens in the eye.

Long sight
In a person with ‘hyperopia’ (long
sight), the image is not correctly
focused onto the retina by the eye
lens. The image is focused behind
the retina, leading to a blurry
image.
How can we correct this?

Correcting long sight
Long sight can be corrected by
using a convex (converging) lens.
This causes the light rays to
converge slightly before they hit
the lens so that they are refracted
perfectly onto the retina.

Power of a lens
The power of a lens can be worked out using the following
equation:
Power = 1
Focal length
Power = Dioptre (D)
Focal length = m

To understand how
objects balance
ALL – State the
definition of a moment
MOST – Perform
moment calculations
objects balance using
the concept of moments

What is a moment?
When the mass is placed on the left-hand side of the see-
saw, it moves down. This is an anticlockwise turn
The turning effect of a force is called a moment
LO: Understand how things balance
pivot

Calculating moments
The moment of a force is calculated from:
Moment = force x distance from pivot
m = f x d
Moment = Newton – Metres (Nm)
Force = Newtons (N)
Distance = metres (m)

Example 1
Gina weighs 500 N and stands on one end of a seesaw.
She is 0.5 m from the pivot. What moment does she
exert?
moment = 500 x 0.5
= 250 Nm
0.5 m
500 N
pivot

Example 2
If a force of 20 N presses down at a distance of 3 m from a
pivot, its moment is:
Moment = 20 N x 3 m = 60 Nm

Example 3
If a force of 30 N presses down at a distance of 4 m from a
pivot, its moment is:
Moment = 30 N x 4 m = 60 Nm

Moments in balance
A seesaw is an example of the principle of moments. This
states that for an object in equilibrium (not moving!) the
sum of all the clockwise moments about any point is
equal to the sum of all the anticlockwise moments about
the same point.
Clockwise moments = anticlockwise moments
W1 x D1 = W2 x D2

Calculating moments
Task: Answer the questions on calculating moments on
the worksheet. The second side is more difficult than the
first!
Moment = force x distance from pivot

What do these objects have in common?

KEYWORDS: centre of mass, line of
symmetry
Understand what is
meant by centre of
mass
ALL – Define the
centre of mass
MOST – be able to find
the centre of mass of
symmetrical objects
SOME – Explain why
objects are designed
to have a low centre of
mass
Starter
What do these objects have
in common?

Centre of Mass
LO: Understand what is meant by centre of mass
For all objects, their
mass is spread out over
the whole object.
However, this is not
useful to us as
Physicists!

Centre of Mass
The centre of mass of
an object is that point
at which the mass may
thought to be
concentrated

Finding the centre of mass
complicated objects can
be incredibly difficult to
find. However, for
simple, symmetrical
objects, the COM can be
easily found!

Centre of mass of symmetrical objects
symmetrical objects
ALWAYS lies along the
line of symmetry of the
object. Where the
object has more than
one line of symmetry,
the COM will be at the
point where the lines of
symmetry intersect

Suspended objects
If you suspend an object
and then release it, it
will soon come to a rest.
When this happens, the
centre of mass will be
directly below the point
of suspension. The
object can be said to be
in equilibrium.
Demo

Irregular shapes
The centre of mass of an
irregular shape can be found by
using the apparatus shown. The
shape is hung from a point and
a plumbline used to draw the
region in which the COM lies.
This is done repeatedly with the
mass hung from different
points. The point where all the
lines intersect is the COM!

KEYWORDS: centre of mass, stability,
Moment, base, tractor
Understand how to
design stable objects
ALL – state features of
stable objects
MOST – Explain what
happens when objects
topple over
design of objects based
on their stability
Starter
Challenge
starter!

The designers of this bus are worried that it will
topple over. They are testing it to find out the
maximum angle it can go to before this happens.
Using your knowledge of science and as many
scientific terms as possible, explain WHY this bus
is likely to topple over easily!
Keywords:
• Centre of mass
• Moment
• Pivot
• Base
• Topple

Stable objects
Although the design of cars
has changed drastically over
the last 100 years, a number
of things have remained
constant. Amongst them is
to keep cars as low as
possible. This means that
the centre of mass of the
car is low and it is less likely
to topple over!
LO: understand how to design stable objects

Why do objects tips over?
The weight of an object acts
through the centre of mass.
As the object is initially
tilted, the weight is causing
an anticlockwise moment
about the pivot. If the
object is let go, the moment
will cause the object to go
back onto its base.

As the object continues to
be tilted, you will reach a
point where the weight will
go exactly through the pivot.

When the object has been
tilted beyond a certain
point, the weight will now
cause a clockwise moment
about the pivot. If the
object is let go, the moment
will cause the object to
topple over!

Designing stable objects
Farmers must be careful
when driving tractors on
slopes. If the slope is too
steep, the tractor may
topple over. To limit the
chances of this happening,
tractors usually have a
large base

Designing stable objects
This bus is being tested to
find the maximum angle it
can be tilted to before it
topples over. This is
important for road safety
as it will affect the
maximum speed that a
driver can go around a
corner.

High chairs
A high chair has a centre
of mass that is very high
off the ground. This can
make the chair very
unstable, particularly
when there is a baby
strapped in! To make sure
the chair does not topple
over, it is designed to have
a wide base.

KEYWORDS: Pressure, force, area, hydraulics
Understand pressure in
liquids
ALL – State the
definition of pressure
MOST – Perform
calculations involving
pressure
pressure is used in
hydraulic machines
Starter
List as many situations as you
can where you might be under
pressure!

Pressure
LO: understand pressure in liquids
Pressure is defined as the force per unit area. The
unit of pressure is the pascal (Pa), which is equal
to one newton per square metre (N/m²)

Calculating pressure
Pressure can be calculated using the following
equation:
Pressure = Force / Area
Pressure = pascals (Pa)
Force = Newtons (N)
Area = metres² (m²)

Hydraulic pressure
Hydraulic pressure is pressure that is caused by a liquid.
Pressure in a liquid is caused by
the weight of the water above.
Pressure in a liquid:
 Acts in all directions
 Increases with depth

Hydraulic pressure
Dams are built with the base of the dam considerably thicker
than the top. Use your knowledge of pressure to explain why.

Demonstration: Archimedes can
The Archimedes can
shows us how the
pressure of a liquid
increases with depth

Hydraulic machines

Hydraulic machines
We can use hydraulic pressure
in machines to make things
move. Liquids are almost
incompressible. This means that
if a force is applied to liquid in
one part of the system, it will
move and transfer the force to
another part of the system. This
can be used to squeeze brakes
or move earth in a digger!

Force multipliers

Force multipliers
The calculation that we
have just done shows
how pressure can be
used in hydraulic
systems to make forces
bigger. However, this
will only work if:
• The liquid is
incompressible
• A2 is bigger than A1

KEYWORDS: centripetal force, radius,
Velocity, tangent
Understand circular
motion
ALL – State situations
where objects move in a
circle
MOST – Explain what is
required for objects to
move in a circle
SOME – Explain what
happens to the
centripetal force due to
changes in radius and
velocity
Starter
Make a mind map of
objects/situations where things
move continuously in a circle

Circular motion
All the situations that
we have just listed
involve circular
motion. The objects
are moving in a circle
of constant radius with
a constant speed.
Is the velocity of the
object the same?
LO: understand circular motion

Requirements of circular motion
For an object to move in
circular motion:
• The velocity is
tangent to the circle
• The velocity changes
as the object moves
around the circle
• The velocity keeps
the object orbiting in
a circle

Centripetal force
When an object moves
with circular motion,
there must be a force
acting on it. This force is
called the centripetal
force and causes the
object to accelerate
towards the centre of
the circle.

What is the centripetal force?
 Electrostatic force…
 Friction…
 Gravity…
 Tension…
 A car travelling around
a bend
 A stone whirled around
on the end of a string
 A planet moving
around the sun
 An electron orbiting
the nucleus

More or less force?
Discuss with the people
on your pod what effect
there will be on the
centripetal force if:
1. The speed of rotation
is increased
2. The radius is
decreased
3. The mass of the
object is increased

More or less force?
If you want to:
1. Increase the speed of
rotation
2. Decrease the radius
3. Increase the mass of
the object
The centripetal force
must also be increased.
To do the opposite, the
centripetal force must be
decreased.

KEYWORDS: oscillating, pendulum,
Frequency, time period
Understand the motion
of a pendulum
ALL – Define the motion
of a pendulum
MOST – Explain how the
time period of a
pendulum can be
increased
SOME – Perform
calculations involving
time period and
frequency

The pendulum
The picture shows a
snapshot of a pendulum in
motion. The pendulum
moves backwards and
forwards and always returns
back to the middle, called
the equilibrium position.
This type of motion is called
oscillating motion.
LO: understand the motion of a pendulum

Time period
The time period of a
pendulum is the time it
takes for a pendulum to
complete one full cycle of
motion. The easiest way to
measure this is the time it
takes for the pendulum to
swing from one side of the
pendulum to the other side
and back again.

What affects the time period?
The factors that affect the
time period of a pendulum
are:
1. The length of the
pendulum
2. The amplitude
(maximum
displacement) of the
swing

Calculating time period
The time period of a pendulum can be calculated
using the following formula:
T = 1 / f
T = Time (s)
f = frequency (Hz)

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