additional science

1. 04/25/16
Physics 2Physics 2
W Richards
The Weald School

2. 04/25/16
Distance, SpeedDistance, Speed
and Timeand Time
Speed = distance (in metres)
time (in seconds)
D
TS
1) Seb walks 200 metres in 40 seconds. What is his speed?
2) Lucy covers 2km in 1,000 seconds. What is her speed?
3) How long would it take Freddie to run 100 metres if he runs
at 10m/s?
4) Sue travels at 50m/s for 20s. How far does he go?
5) Hannah drives her car at 85mph (about 40m/s). How long
does it take her to drive 20km?

3. 04/25/16
Distance-time graphsDistance-time graphs
40
30
20
10
0
20 40 60 80 100
4) Diagonal line
downwards =
3) Steeper diagonal line =1) Diagonal line =
2) Horizontal line =
Distance
(metres)
Time/s

4. 04/25/16
40
30
20
10
0
20 40 60 80 100
1) What is the speed during the first 20 seconds?
2) How far is the object from the start after 60 seconds?
3) What is the speed during the last 40 seconds?
4) When was the object travelling the fastest?
Distance
(metres)
Time/s

5. 04/25/16
Speed vs. VelocitySpeed vs. Velocity
Speed is simply how fast you are travelling…
Velocity is “speed in a given direction”…
This car is travelling at a
speed of 20m/s
This car is travelling at a
velocity of 20m/s east

6. 04/25/16
AccelerationAcceleration V-U
TA
Acceleration = change in velocity (in m/s)
(in m/s2
) time taken (in s)
1) A cyclist accelerates from 0 to 10m/s in 5 seconds. What
is her acceleration?
2) A ball is dropped and accelerates downwards at a rate of
10m/s2
for 12 seconds. How much will the ball’s velocity
increase by?
3) A car accelerates from 10 to 20m/s with an acceleration of
2m/s2
. How long did this take?
4) A rocket accelerates from 1,000m/s to 5,000m/s in 2
seconds. What is its acceleration?

7. 04/25/16
Velocity-time graphsVelocity-time graphs
80
60
40
20
0
10 20 30 40 50
Velocity
m/s
T/s
1) Upwards line =
2) Horizontal line = 3) Upwards line =
4) Downward line =

8. 04/25/16
80
60
40
20
0
1) How fast was the object going after 10 seconds?
2) What is the acceleration from 20 to 30 seconds?
3) What was the deceleration from 30 to 50s?
4) How far did the object travel altogether?
10 20 30 40 50
Velocity
m/s
T/s

9. 04/25/16
Balanced and unbalanced forcesBalanced and unbalanced forces
Consider a camel standing on a road.
What forces are acting on it?
Weight
Reaction
These two forces would be equal –
we say that they are BALANCED.
The camel doesn’t move anywhere.

10. 04/25/16
Balanced and unbalanced forcesBalanced and unbalanced forces
What would happen if we took the
road away?
Weight
Reaction

11. 04/25/16
Balanced and unbalanced forcesBalanced and unbalanced forces
What would happen if we took the
road away?
The camel’s weight is no longer
balanced by anything, so the camel
falls downwards…
Weight

12. 04/25/16
What would happen if we took the
road away?
The camel’s weight is no longer
balanced by anything, so the camel
falls downwards…
Balanced and unbalanced forcesBalanced and unbalanced forces

13. 04/25/16
Air ResistanceAir Resistance
Air resistance is a force that opposes motion through air. The
quicker you travel, the bigger the air resistance:
The same applies to a body falling through a liquid (called
“drag” or “upthrust”).

14. 04/25/16
Balanced and unbalanced forcesBalanced and unbalanced forces

15. 04/25/16
Balanced and unbalanced forcesBalanced and unbalanced forces
1) This animal is either
________ or moving
with _____ _____…
4) This animal is…
2) This animal is getting
_________…
3) This animal is getting
_______….

16. 04/25/16
Resultant ForceResultant Force
Calculate the resultant force of the following:
500N 100N 700N 600N
700N 700N
200N
800N 800N
100N
50N

17. 04/25/16
Force and accelerationForce and acceleration
If the forces acting on an object
are unbalanced then the object will
accelerate, like these wrestlers:
Force (in N) = Mass (in kg) x Acceleration (in m/s2
)
F
AM

18. 04/25/16
Force, mass and accelerationForce, mass and acceleration
1) A force of 1000N is applied to push
a mass of 500kg. How quickly does
it accelerate?
2) A force of 3000N acts on a car to
make it accelerate by 1.5m/s2
. How
heavy is the car?
3) A car accelerates at a rate of
5m/s2
. If it weighs 500kg how
much driving force is the engine
applying?
4) A force of 10N is applied by a boy
while lifting a 20kg mass. How
much does it accelerate by?
F
AM

19. 04/25/16
Terminal VelocityTerminal Velocity
Consider a skydiver:
1) At the start of his jump the air
resistance is _______ so he
_______ downwards.
2) As his speed increases his air
resistance will _______
3) Eventually the air resistance will be
big enough to _______ the
skydiver’s weight. At this point
the forces are balanced so his
speed becomes ________ - this is
called TERMINAL VELOCITY
Words – increase, small,
constant, balance, accelerates

20. 04/25/16
Terminal VelocityTerminal Velocity
Consider a skydiver:
4) When he opens his parachute the
air resistance suddenly ________,
causing him to start _____ ____.
5) Because he is slowing down his air
resistance will _______ again
until it balances his _________.
The skydiver has now reached a
new, lower ________ _______.
Words – slowing down, decrease,
increases, terminal velocity, weight

21. 04/25/16
Velocity-time graph for terminal velocity…Velocity-time graph for terminal velocity…
Velocity
Time
Speed
increases…
Terminal
velocity
reached…
Parachute opens –
diver slows down
New, lower terminal
velocity reached
Diver hits the ground
On the Moon

22. 04/25/16
Weight vs. MassWeight vs. Mass
Earth’s Gravitational Field Strength is 10N/kg. In other
words, a 1kg mass is pulled downwards by a force of 10N.
W
gM
Weight = Mass x Gravitational Field Strength
(in N) (in kg) (in N/kg)
1) What is the weight on Earth of a book with mass 2kg?
2) What is the weight on Earth of an apple with mass 100g?
3) Dave weighs 700N. What is his mass?
4) On the moon the gravitational field strength is 1.6N/kg. What will
Dave weigh if he stands on the moon?

23. 04/25/16
Stopping a car…Stopping a car…
Braking
distance
Too much
alcoholThinking
distance
(reaction time)
Tiredness
Too many
drugs
Wet roads
Driving too
fast
Tyres/brakes
worn out
Icy roads
Poor
visibility

24. 04/25/16
Work doneWork done
When any object is moved around work will need to be
done on it to get it to move (obviously).
We can work out the amount of work done in moving an
object using the formula:
Work done = Force x distance moved
in J in N in m W
DF

25. 04/25/16
Example questionsExample questions
1. Bori pushes a book 5m along the table with a force of 5N.
He gets tired and decides to call it a day. How much work
did he do?
2. Alicia lifts a laptop 2m into the air with a force of 10N.
How much work does she do?
3. Martin does 200J of work by pushing a wheelbarrow with a
force of 50N. How far did he push it?
4. Chris cuddles his cat and lifts it 1.5m in the air. If he did
75J of work how much force did he use?
5. Carl drives his car 1000m. If the engine was producing a
driving force of 2000N how much work did the car do?

26. 04/25/16
Elastic Potential EnergyElastic Potential Energy
Elastic potential energy is the
energy stored in a system
when work is done to change
its shape, e.g:

27. 04/25/16
Kinetic energyKinetic energy
Any object that moves will have kinetic energy.
The amount of kinetic energy an object has can be found using
the formula:
Kinetic energy = ½ x mass x velocity squared
in J in kg in m/s
KE = ½ mv2

28. 04/25/16
Example questionsExample questions
1) Nicole drives her car at a speed of 30m/s. If the
combined mass of her and the car is 1000kg what is her
kinetic energy?
2) Shanie rides her bike at a speed of 10m/s. If the
combined mass of Shanie and her bike is 80kg what is her
kinetic energy?
3) Dan is running and has a kinetic energy of 750J. If his
mass is 60kg how fast is he running?
4) George is walking to town. If he has a kinetic energy of
150J and he’s walking at a pace of 2m/s what is his mass?

29. 04/25/16
Random questions…Random questions…
1) Sophie tries to run 100m in 12 seconds and succeeds. How fast did she
run?
2) Tommy accelerates at a rate of 2m/s2
for 3 seconds. If he started at
10m/s what was his final speed?
3) Charlie decides to lift his book up into the air. His book has a mass of
100g and he lifts it 50cm. Calculate the work done.
4) Lewis accelerates from 0 to 10m/s in 5 seconds. If his mass is 70kg
how much force did his legs apply?
5) Rachel rides 1km at a speed of 20m/s. How long did the journey take?
6) Claire thinks it’s funny to push James with a force of 120N. If James
has a mass of 60kg calculate his acceleration.
7) Lauren slams on the brakes on her bike and her brakes do 20,000J of
work. If the combined mass is 100kg what speed was she travelling at?
8) Tom has a mass of 75kg. If he accelerates from 10 to 20m/s in 2s how
much force did he apply?

30. 04/25/16
Random questions…Random questions…
9) Georgina amuses herself by throwing things at Sarah. If she throws a
ball with a speed of 20m/s and the distance between her and Sarah is
5m how long will it take to reach her?
10) Mr Richards throws calculators around the room with a force of 20N.
If each calculator has a mass of 200g calculate the acceleration.
11) Sam has a mass of 70kg. What is his weight on Earth, where the
gravitational field strength is 10N/kg?
12) Zak does some work by pushing a box around with a force of 1N. He
does 5J of work and decides to call it a day. How far did he push it?
13) On the moon Matt might weigh 112N. If the gravitational field
strength on the moon is 1.6N/kg what is his mass? What will he weigh
on Earth?
14) Dan likes bird watching. He sees a bird fly 100m in 20s. How fast was
it flying?
15) How much kinetic energy would Richard have if he travelled at a speed
of 5m/s and has a mass of 70kg?

31. 04/25/16
MomentumMomentum
Any object that has both mass and
velocity has MOMENTUM. Momentum
(symbol “p”) is simply given by the formula:
Momentum = Mass x Velocity
(in kgms-1) (in kg) (in ms-1)
P
VM
What is the momentum of the following?
1) A 1kg football travelling at 10ms-1
2) A 1000kg Ford Capri travelling at 30ms-1
3) A 20g pen being thrown across the room at 5ms-1
4) A 70kg bungi-jumper falling at 40ms-1

32. 04/25/16
Conservation of MomentumConservation of Momentum
In any collision or explosion momentum is conserved (provided that there
are no external forces have an effect). Example question:
Two cars are racing around the M25. Car A collides with the back of car B
and the cars stick together. What speed do they move at after the
collision?
Mass = 1000kg Mass = 800kg
Speed = 50ms-1
Speed = 20ms-1
Momentum before = momentum after…
…so 1000 x 50 + 800 x 20 = 1800 x V…
…V = 36.7ms-1
Mass = 1800kg Speed = ??ms-1

33. 04/25/16
Momentum in different directionsMomentum in different directions
What happens if the bodies are moving in opposite directions?
Speed = 50ms-1
Mass = 1000kg
Speed = 20ms-1
Mass = 800kg
Momentum is a VECTOR quantity, so the momentum of the
second car is negative…
Total momentum = 1000 x 50 – 800 x 20 = 34000 kgms-1
Speed after collision = 34000 kgms-1
/ 1800 = 18.9ms-1

34. 04/25/16
Another exampleAnother example
Consider the nuclear decay of Americium-241:
Am241
95
α4
2
If the new neptunium atom moves away at
a speed of 5x105
ms-1
what was the speed
of the alpha particle?
Np237
93

35. 04/25/16
More questions…More questions…
1) A white snooker ball moving at 5m/s strikes a red ball and pots it.
Both balls have a mass of 1kg. If the white ball continued in the same
direction at 2m/s what was the velocity of the red ball?
2) A car of mass 1000kg heading up the M1 at 50m/s collides with a
stationary truck of mass 8000kg and sticks to it. What velocity does
the wreckage move forward at?
3) A defender running away from a goalkeeper at 5m/s is hit in the back
of his head by the goal kick. The ball stops dead and the player’s speed
increases to 5.5m/s. If the ball had a mass of 500g and the player had
a mass of 70kg how fast was the ball moving?
4) A gun has a recoil speed of 2m/s when firing. If the gun has a mass of
2kg and the bullet has a mass of 10g what speed does the bullet come

36. 04/25/16
Force and momentumForce and momentum
Newton’s second law of motion says that the force acting on
an object is that object’s rate of change of momentum. In
other words…
∆mv
TF
Force = Change in momentum
Time
(in N)
(in kgm/s)
(in s)
For example, David Beckham takes a free kick by kicking a stationary
football with a force of 40N. If the ball has a mass of 0.5kg and his
foot is in contact with the ball for 0.1s calculate:
1) The change in momentum of the ball (its impulse),
2) The speed the ball moves away with
Also called “impulse”

37. 04/25/16
Example questionsExample questions
1) Ben likes playing golf. He strikes a golf ball with a force of
80N. If the ball has a mass of 200g and the club is in
contact with it for 0.2s calculate a) the change in
momentum of the golf ball, b) its speed.
2) Nick thinks it’s funny to hit tennis balls at Tom. He strikes
a serve with a force of 30N. If the ball has a mass of
250g and the racket is in contact with it for 0.15s calculate
the ball’s change in momentum and its speed.
3) Dan takes a dropkick by kicking a 0.4kg rugby ball away at
10m/s. If his foot was in contact with the ball for 0.1
seconds calculate the force he applied to the ball.
4) Simon strikes a 200g golf ball away at 50m/s. If he
applied a force of 50N calculate how long his club was in
contact with the ball for.

38. 04/25/16
Safety featuresSafety features
Let’s use Newton’s Second Law to explain how airbags work:
∆mv
TF
Basically:
1) The change in momentum is the same with or without an
airbag
2) But having an airbag increases the time of the collision
3) Therefore the force is reduced

39. 04/25/16
Static ElectricityStatic Electricity
Static electricity is when charge “builds up” on an object and
then stays “static”. How the charge builds up depends on what
materials are used:
+ -
+-
+
+-
-
-
+
+
+
-
-
+
+
+
-
-
-

40. 04/25/16
Static ElectricityStatic Electricity
+
+
+ -
-
-
-
-
--
-
-

41. 04/25/16
Van de Graaf generatorsVan de Graaf generators

42. 04/25/16
Uses of Static – Smoke PrecipitatorsUses of Static – Smoke Precipitators
-
-
-
-
-
-
+ +
+
Chimney
Negatively
charged
plates
Positively
charged
grid

43. 04/25/16
Uses and dangers of Static ElectricityUses and dangers of Static Electricity
Find out how static electricity is used in the following:
1) Photocopiers
2) Paint sprayer
Find out how static electricity is dangerous in the following
situations:
1) Fuel pipes
2) Hospitals

44. 04/25/16
Circuit SymbolsCircuit Symbols
VA
Battery
Cell
Fuse
Resistor
LDR
Voltmeter
Ammeter
Variable
resistor
Diode
Switch
Bulb
Thermistor

45. 04/25/16
Electric CurrentElectric Current
Electric current is a flow
of negatively charged
particles (i.e. electrons).
Note that
electrons go
from negative
to positive
-+ e-
e-
By definition, current is “the
rate of flow of charge”

46. 04/25/16
Basic ideas…Basic ideas…
Electric current is when electrons start to flow around a
circuit. We use an _________ to measure it and it is
measured in ____.
Potential difference (also called _______) is
how big the push on the electrons is. We use a
________ to measure it and it is measured in
______, a unit named after Volta.
Resistance is anything that resists an electric current. It is
measured in _____.
Words: volts, amps, ohms, voltage, ammeter, voltmeter

47. 04/25/16
More basic ideas…More basic ideas…
If a battery is
added the current
will ________
because there is a
greater _____ on
the electrons
If a bulb is added
the current will
_______ because
there is greater
________ in the
circuit

48. 04/25/16
Current in a series circuitCurrent in a series circuit
If the current
here is 2
amps…
The
current
here will
be…
The current
here will
be…
And the
current
here will
be…
In other words, the current in a series
circuit is THE SAME at any point

49. 04/25/16
Current in a parallel circuitCurrent in a parallel circuit
A PARALLEL circuit is one where the current has a “choice
of routes”
Here comes the current…
And the rest will
go down here…
Half of the current
will go down here
(assuming the bulbs
are the same)…

50. 04/25/16
Current in a parallel circuitCurrent in a parallel circuit
If the
current
here is 6
amps
The current
here will be…
The current
here will be…
The current
here will be…
And the
current here
will be…

51. 04/25/16
Some example questions…Some example questions…
3A
6A

52. 04/25/16
Voltage in a series circuitVoltage in a series circuit
V
V V
If the voltage
across the
battery is 6V…
…and these
bulbs are all
identical…
…what will the
voltage across
each bulb be? 2V

53. 04/25/16
Voltage in a series circuitVoltage in a series circuit
V
V
If the voltage
across the
battery is 6V…
…what will the
voltage across
two bulbs be?
4V

54. 04/25/16
Voltage in a parallel circuitVoltage in a parallel circuit
If the voltage across
the batteries is 4V…
What is the
voltage here?
And here?
V
V
4V
4V

55. 04/25/16
SummarySummary
In a SERIES circuit:
Current is THE SAME at any point
Voltage SPLITS UP over each component
In a PARALLEL circuit:
Current SPLITS UP down each “strand”
Voltage is THE SAME across each”strand”

56. 04/25/16
An example question:An example question:
V1
V2
6V
3A
A1
A2
V3
A3

57. 04/25/16
Another example question:Another example question:
V1
V2
10V
3A
A1
A2
V3
A3

58. 04/25/16
Georg Simon Ohm
1789-1854
ResistanceResistance
Resistance is anything that will
RESIST a current. It is measured
in Ohms, a unit named after me.
The resistance of a component can be
calculated using Ohm’s Law:
Resistance = Voltage (in V)
(in Ω) Current (in A)
V
RI

59. 04/25/16
An example question:An example question:
V
A
1) What is the resistance across
this bulb?
2) Assuming all the bulbs are the
same what is the total resistance
in this circuit?
Voltmeter
reads 10V
Ammeter
reads 2A

60. 04/25/16
More examples…More examples…
12V
3A
3A
6V
4V
2A
1A
2V
What is the
resistance of
these bulbs?

61. 04/25/16
ResistanceResistance
Resistance is anything that opposes an electric current.
Resistance (Ohms, Ω) = Potential Difference (volts, V)
Current (amps, A)
What is the resistance of the following:
1) A bulb with a voltage of 3V and a current of 1A.
2) A resistor with a voltage of 12V and a current of 3A
3) A diode with a voltage of 240V and a current of 40A
4) A thermistor with a current of 0.5A and a voltage of
10V

62. 04/25/16
Resistors, bulbs and diodesResistors, bulbs and diodes

63. 04/25/16
Current-Voltage GraphsCurrent-Voltage Graphs
Voltage on
powerpack/V
Current/A Voltage/V
12
10
…
0
…
-10
-12

64. 04/25/16
Current-voltage graphsCurrent-voltage graphs
I
V
I
V
I
V
1. Resistor 3. Diode
2. Bulb
Current
increases in
proportion
to voltage
As voltage increases
the bulb gets hotter
and resistance
increases
A diode only lets
current go in one
direction – it has
very high
resistance in the
other direction

65. 04/25/16
LDRs and ThermistorsLDRs and Thermistors

66. 04/25/16
Two simple components:Two simple components:
2) Thermistor –
resistance DECREASES
when temperature
INCREASES
1) Light dependant
resistor – resistance
DECREASES when light
intensity INCREASES
Resistance
Amount of light
Resistance
Temperature

67. 04/25/16
Wiring a plugWiring a plug
Earth
wire
Neutral
wire
Insulation
Live
wire
Fuse
1.
2.
3.
4.
5.
6. Cable
grip
The live wire of a plug alternates
between positive and negative
potential relative to the Earth
The neutral wire of a plug stays at
a potential close to zero relative
to the Earth

68. 04/25/16
DC and ACDC and AC
DC stands for “Direct
Current” – the current only
flows in one direction:
AC stands for “Alternating
Current” – the current
changes direction 50 times
every second (frequency =
50Hz)
1/50th
s
230V
V
V
Time
T

69. 04/25/16
Using an oscilloscopeUsing an oscilloscope
Q. What is the voltage and
frequency of this supply?
This number tells
you how many
seconds each square
on the horizontal
axis represents
This number tells
you how many
volts each square
on the vertical
axis represents

70. 04/25/16
FusesFuses
Fuses are _______ devices. If
there is a fault in an appliance
which causes the ____ and neutral
(or earth) wire to cross then a
______ current will flow through
the _____ and cause it to _____.
This will break the _______ and
protect the appliance and user
from further _____.
Words – large, harm, safety, melt, live, circuit, fuse

71. 04/25/16
Power and fusesPower and fuses
Power is “the rate of doing work”.
The amount of power being used in
an electrical circuit is given by: P
IV
Power = voltage x current
in W in V in A
Using this equation we can work out the fuse rating for any
appliance. For example, a 3kW (3000W) fire plugged into a
240V supply would need a current of _______ A, so a
_______ amp fuse would be used (fuse values are usually
3, 5 or 13A).

72. 04/25/16
Power and fusesPower and fuses
Copy and complete the following table:
Appliance Power rating
(W)
Voltage (V) Current
needed (A)
Fuse needed
(3, 5 or 13A)
Toaster 960 240
Fire 2000 240
Hairdryer 300 240
Hoover 1000 240
Computer 100 240
Stereo 80 240

73. 04/25/16
Energy and PowerEnergy and Power
The POWER RATING of an appliance is simply how much
energy it uses every second.
In other words, 1 Watt = 1 Joule per second
E
TP
E = Energy (in joules)
P = Power (in watts)
T = Time (in seconds)

74. 04/25/16
Some example questionsSome example questions
1) What is the power rating of a light bulb that transfers 120
joules of energy in 2 seconds?
2) What is the power of an electric fire that transfers
10,000J of energy in 5 seconds?
3) Farhun runs up the stairs in 5 seconds. If he transfers
1,000,000J of energy in this time what is his power rating?
4) How much energy does a 150W light bulb transfer in a) one
second, b) one minute?
5) Shaun’s brain needs energy supplied to it at a rate of 40W.
How much energy does it need during a physics lesson?
6) Damien’s brain, being more intelligent, only needs energy at
a rate of about 20W. How much energy would his brain use
in a normal day?

75. 04/25/16
Earth wiresEarth wires
Earth wires are always used if an appliance has a _____
case. If there is a _____ in the appliance, causing the live
wire to ______ the case, the current “_______” down the
earth wire and the ______ blows.
Words – fuse, fault, metal, surges, touch

76. 04/25/16
Charge (Q)Charge (Q)
As we said, electricity is when electrons move around a
circuit and carry energy with them. Each electron has a
negative CHARGE. Charge is measured in Coulombs (C).
We can work out how much charge flows in a circuit using
the equation:
Q
TI
Charge = current x time
(in C) (in A) (in s)

77. 04/25/16
Example questionsExample questions
Charge (C) Current (A) Time (s)
5 2
0.4 1
20 0.5
50 250
3 60
1) A circuit is switched on for 30s with a current of 3A. How much
charge flowed?
2) During electrolysis 6A was passed through some copper chloride
and a charge of 1200C flowed. How long was the experiment on
for?
3) A bed lamp is switched on for 10 minutes. It works on a current of
0.5A. How much charge flowed?

78. 04/25/16
Energy and chargeEnergy and charge
The amount of energy that flows in a circuit will depend on
the amount of charge carried by the electrons and the
voltage pushing the charge around:
E
QV
Energy transferred = charge x voltage
(in J) (in C) (in V)

79. 04/25/16
Example questionsExample questions
1) In a radio circuit a voltage of 6V is applied and a charge
of 100C flows. How much energy has been transferred?
2) In this circuit the radio drew a current of 0.5A. How
long was it on for?
3) A motor operates at 6V and draws a current of 3A. The
motor is used for 5 minutes. Calculate: a) The motor’s
resistance, b) the charge flowing through it, c) the
energy supplied to it
4) A lamp is attached to a 12V circuit and a charge of
1200C flows through it. If the lamp is on for 10 minutes
calculate a) the current, b) the resistance, c) the
energy supplied to the bulb.

80. 04/25/16
Random questionsRandom questions
1) A battery has a voltage of 12V and it puts a current of 3A
through a bulb. What is the bulb’s resistance?
2) Another bulb transfers 120C of charge in 2 minutes. What
was the current through it?
3) A powerpack transfers 2,000J to a motor. If the motor
ran on a voltage of 50V how much charge was transferred?
4) A hairdryer runs on a 50Hz power supply. If it has a power
rating of 200W what fuse should it have?
5) An electric fire transfers 3MJ of energy. If it has a
power rating of 2KW calculate how long it was on for, the
current it ran on (assuming it was connected to the mains
supply) and the amount of charge it transferred.

81. 04/25/16
Structure of the atomStructure of the atom
A hundred years ago people thought
that the atom looked like a “plum
pudding” – a sphere of positive
charge with negatively charged
electrons spread through it…
I did an experiment (with my
colleagues Geiger and Marsden) that
proved this idea was wrong. I called it
the “Scattering Experiment”
Ernest Rutherford, British scientist:

82. 04/25/16
The Rutherford Scattering ExperimentThe Rutherford Scattering Experiment
Alpha
particles
(positive
charge, part
of helium
atom)
Thin gold
foil
Most particles passed
through, 1/8000 were
deflected by more than
900
Conclusion – atom is made up of a small,
positively charged nucleus surrounded by
electrons orbiting in a “cloud”.

83. 04/25/16
The structure of the atomThe structure of the atom
ELECTRON –
negative, mass
nearly nothing
PROTON –
positive, same
mass as
neutron (“1”)
NEUTRON –
neutral, same
mass as proton
(“1”)

84. 04/25/16
The structure of the atomThe structure of the atom
Particle Relative Mass Relative Charge
Proton 1 +1
Neutron 1 0
Electron 0 -1
MASS NUMBER = number of
protons + number of neutrons
SYMBOL
PROTON NUMBER = number of
protons (obviously)

85. 04/25/16
IsotopesIsotopes
An isotope is an atom with a different number of neutrons:
Each isotope has 8 protons – if it didn’t then it just
wouldn’t be oxygen any more.
Notice that the mass number is different. How many
neutrons does each isotope have?
A “radioisotope” is simply an isotope that is radioactive –
e.g. carbon 14, which is used in carbon dating.

86. 04/25/16
Background RadiationBackground Radiation
Radon gas
Food
Cosmic rays
Gamma rays
Medical
Nuclear power
13% are
man-made

87. 04/25/16
Types of radiationTypes of radiation
1) Alpha (α) – an atom decays into a new
atom and emits an alpha particle (2
protons and 2 ______ – the nucleus of a
______ atom)
2) Beta (β) – an atom decays into a new
atom by changing a neutron into a
_______ and electron. The fast moving,
high energy electron is called a _____
particle.
3) Gamma – after α or β decay surplus
______ is sometimes emitted. This is
called gamma radiation and has a very
high ______ with short wavelength.
The atom is not changed.
Unstable
nucleus
Unstable
nucleus
Unstable
nucleus
New
nucleus
New
nucleus
New
nucleus
Alpha
particle
Beta
particle
Gamma
radiation
Words – frequency, proton,
energy, neutrons, helium, beta

88. 04/25/16
Nuclear fissionNuclear fission
Uranium or
plutonium
nucleus
Unstable
nucleus
New nuclei
(e.g. barium
and krypton)
More
neutrons
Neutron

89. 04/25/16
Chain reactionsChain reactions
Each fission reaction releases
neutrons that are used in
further reactions.

90. 04/25/16
Nuclear Fusion in starsNuclear Fusion in stars
Proton Neutron