Physics Unit 3

Year Long Plan

First Ten Minutes (Everyday) – Revision, questions

Then Learning/Pracs Homework… 40+ Club

What you need

Textbook Student Book Scientific Calculator

Topics

Unit 3: Motion Electronics and Photonics

Unit 4: Electric Power Interaction of light and matter

Detailed Study (Homework) …Plus an extra project…?

Project…?

Print off News article. Youtube video

Area of Study One

Motion in One and Two Dimensions

The Plan

Review of Motion Projectile Motion Momentum Energy Circular Motion Gravity and Satellites

Review of Motion

Place the following into a linked “Concept Map”. Label all the arrows that link the concepts together.

Forces, Newton’s First Law, Newtons Second Law, Newton’s Third Law, Eqns of motion, mometum, velocity, acceleration, Impulse, Work, kinetic energy, potential energy, Types of forces, Gravity, Normal Force, Springs, Inclined Planes

Review

CUPS 2

Scalars and Vectors

Scalar: Physical quantity represented by only a number

Eg Mass, temperature Vector: Physical quantity requiring a

direction AND number (magnitude) Eg Force, velocity

Distance and Displacement

e.g. total distance of travel

• DistanceLength of an object has travelled

• Displacement

e.g. final position – initial position

Change in position of an object.

Scalar

Vector

Speed or Velocity?

Speed: Scalar quantity.

Velocity: Vector quantity. Magnitude AND Direction

Magnitude only

Velocity

To find velocity, when travelling at a constant velocity (no acceleration) OR to find the average velocity:

Questions

Tim travels 80m North up North Rd. He then turns and travels 60m East along east road. This travel takes 24s.

1) Draw a diagram of the situation2) Calculate the total distance3) Calculate the total displacement4) Calculate the average speed5) Calculate the average velocity

Centre of mass motion

Usain Bolt runs the 100m with a speed of 10ms-1

Do all parts of his body move at 10ms-

1? His arms? His legs? His Head? No. His arms often move faster (and

slower) than 10ms-1

Centre of Mass Motion

As physicists, we simplify the problem, and approximate Usain Bolt as a point, at his centre of mass.

So all calculations of his speed are based on his centre of mass

A Statistician, Engineer and Physicist go to the horse track. Each have their system for betting on the winner and they're sure of it. After the race is over, the Statistician wanders into the nearby bar, defeated. He notices the Engineer, sits down next to him, and begins lamenting: "I don't understand it. I tabulated the recent performance of all these horses, cross-referenced them with trends for others of their breed, considered seasonal variability, everything. I couldn't have lost.“ "Yeah," says the Engineer, "well, forget that. I ran simulations based on their weight, mechanical ratios, performance models, everything, and I'm no better off.“ Suddenly, they notice a commotion in the corner. The Physicist is sitting there, buying rounds and counting his winnings. The Engineer and Statistician decide they've got to know, so they shuffle over and ask him, "what's your secret, how'd you do it?“ The Physicist leans back, takes a deep breath, and begins, "Well, first I assumed all the horses were spherical and identical..."

Acceleration

Acceleration is a measure of how much velocity changes over time

Change in velocity: Acceleration:𝑎=

𝑣−𝑢𝑡

=Δ𝑣𝑡

Graphing motion

We can graph either the displacement, velocity, acceleration as time changes

The Gradient of a graph is the slope.

The area under the graph is the solid area between the line and the axis

Eg …

Positive Slope/ Gradient

Zero Slope/ Gradient

Negative Slope/ Gradient

Area under graph

Graphing Motion

Prac: Graphing Motion

Displacement-Time Graph

A puppy runs after a stick. It runs 10m to the stick (it takes 10s). It then waits by the stick for 10s, and finally brings the stick back to its owner over 10s.

Draw a displacement-time graph for this scenario

Displacement-Time Graph

Displacement-Time Graphs

Gradient of the displacement-time graph is the velocity

Questions:1) Calculate the velocity over the first 10s2) Calculate the velocity over the next 10s3) Calculate the velocity over the last 10s4) Calculate the average velocity over the

full 30s

Velocity-Time Graph

Gradient of a velocity-time graph is acceleration

Area under the velocity graph is the displacement

Velocity-Time Graph

1) What is the initial velocity?2) What is the change in velocity over

the 30s of motion3) What is the acceleration?4) Is this a constant acceleration?5) What is the total displacement

between 0 and 30s?

Acceleration-Time Graph

The area under an acceleration-time graph is the change in velocity.

Acceleration-Time Graph

1) What is the acceleration at 0s?2) What is the acceleration at 10s?3) What could this graph be describing?4) Find the change in velocity between 0s

and 10s5) If the initial velocity is 2ms-1, what is

the velocity after 10s?

Questions

Draw a displacement-time, velocity-time, and acceleration-time graph for the following:

Sky diver – no air resistance Sky diver – air resistance Person walking at a constant speed

along a path Person 20m away from their house,

standing still

Equations of Motion

Any object moving with a constant acceleration, use the equations of motion

Example

A car accelerates from rest for 10s at an acceleration of 1.5ms-2

What is the final speed? What distance does the car travel over

this time

Questions

1) A car, travelling at 30ms-1, accelerates to 40ms-1 in order to pass a slower car. This acceleration takes 20s. What distance does he travel during this acceleration?

2) Q4 [Pg 12] A car travelling at a constant speed of 80km/h passes a stationary motorcycle policeman. The policeman sets of in pursuit, accelerating uniformly to 80km/h in 10s and reaching a constant speed of 100km/h after a further 5s. At what time will the policeman catch up with the car.

3) Extension question: Mr McGovern is driving down a country road at 100km/h when a beautiful duck steps out 75m in front of his car. His reaction time is 0.6s, then he applies the brakes, decelerating at 15ms-2. Will the duck live?

Vertical Motion

Vertical motion is accelerated motion where the acceleration equals gravity (10ms-2)

Vertical Motion

How high does the tennis ball go?1) Time how long it takes to get to the top of

its flight2) What was the initial velocity?3) How high did the ball go?

4) After the ball left the hand, draw the forces acting on it

5) When the ball was at the top of its flight, draw the forces acting on it

Question

A footy ball is kicked vertically upwards with an initial speed of 22ms-1

How high does it reach? After what time does it hit the ground

again?

Forces

When we add all the forces acting on a body, we add the forces head to tail

Forces

The total force is found by drawing a new arrow from the tail of the first to the head of the last

Find the total forces

Q3 2012

A metal ring is to be held stationary by three forces. Which configuration would make the ring stationary, and why?

Newton’s Laws

First Law: Unless acted on by a net force, an object will continue its motion (whether that’s stationary or constant velocity New Name: Second Law: If acted on by a net force,

an object will accelerate New Name:

Newton’s Laws

Third Law: For every action force on object A, there is an equal and opposite reaction force on object B

New Name:

Newton’s Laws

Why is there misunderstanding in Newton’s Laws?

Rules for next 6 examples. Quietly think of which answer you like. Text in answer Then we will work together to decide how

most people think… And what Newton’s Laws predict the

answer should be

Newton’s Laws: Example 1

Victoria Azerenka throws a tennis ball upwards for her serve. Consider the forces on the tennis ball after it has left the hand, but before she hits it on the way down. Is there…?

a) A downwards force of gravity, along with a steady decreasing upwards force

b) A steadily decreasing upward force from the moment it leaves her hand until it reaches its highest point, on the way down a steadily increasing downwards force of gravity

c) An almost constant downwards force of gravity

What do you think the answer is? What do you think most of the general

population will think? What answer does Newton’s Laws

predict?

An elevator is being lifted by a steel cable at a constant speed. The forces on the elevator are…

a) The upwards force of the cable is greater than the downward force of gravity

b) The upwards force of the cable is equal to the downwards force of gravity

c) The upwards force of the cable is smaller than the downwards force of gravity

d) None of the above: The elevator goes up simply because the cable is being shortened

predict?

A big truck and a small car collide head on.a) The truck exerts a bigger force on the

car than the car onto the truckb) The car exerts a bigger force on the

truck than the truck on the carc) The truck exerts a force on the car, but

the car doesn’t exert one on the truckd) They exert an equal force on each other

predict?

A stationary ice hockey puck is hit. It travels in a straight line along the frictionless ice.After leaving the hockey stick, does the puck …?a) Speed up as there is no frictionb) Travel at a constant speed, and would only

be stopped by the edge of the ice rinkc) Slow down as the force of gravity works

against itd) Slows down as it runs out of force from the

hockey stick hit

predict?

Newtons Laws: Example 5

The same puck is travelling at a constant speed from (a) to (b). At (b) another stick gives it a swift hit in the direction shown. What is the new direction of the puck?

What is the new direction of the puck?

predict?

Demo: A pulley is set up with a string connecting two weights of equal masses. But the masses are at different heights. What happens…?

a) Nothing movesb) The mass on the right pulls down (and the

mass on the left goes up), but at a constant speed

c) The mass on the right pulls down (and the mass on the left goes up), but at an accelerated rate.

d) The mass on the left pulls down (and the mass on the right goes up), but at a constant speed

e) The mass on the left pulls down (and the mass on the right goes up), but at an accelerated rate.

predict?

Newton’s Third Law

Recall: For every action force on object A, there is an equal and opposite reaction force on object B

What is the action/reaction pair for … Eg

Force on car is equal and opposite to force on truck

What is the action/reaction pair for … [Hint: Draw each situation first]

Hitting a hockey puck Jumping up (at the moment of jumping) Falling back down… A book on a table

Common misconception… The action/reaction pair for gravity is

NOT the normal force… Why? They are acting on the same

body!(Draw 1N book, 10N table)

Experiment

Forces, Pulleys and String

Newton’s Laws

CUPS 3, 4, 5. [Monash University] Reminder, print A3 sheets

Inclined Plane

Experiment

Normal Force and Inclined Planes

A normal force (FN or N) always acts at RIGHT ANGLES to a surface.

Draw in the normal forces acting on the circles below:

Normal Force on an Incline

Draw the force of gravity on the ball Is the normal force

bigger/same/smaller than gravity?

Normal Force on an incline

We know that the ball accelerates down the ramp. So the normal doesn’t balance out gravity!

Draw the direction of acceleration Draw in the direction of the total force

Normal Force on an incline

Show how the two forces acting on the ball add to give the total force

Normal Force on an Incline

Draw in the right angle Draw in the angle of the ramp What is the size of the total force?

Questions from Exams

Sample Q 3b Sample Q 6a & 6c 2012 Q 4a, b 2012 Q 5a – d 2011 Q 7, 8

Projectile Motion

… And the effects of air resistance

Projectile Motion

Projectile motion is made simple because we can deal separately with an object’s horizontal and vertical components of its velocity.

𝑣=20𝑚𝑠−1

Projectile Motion

𝑣 𝑥

𝑣=20𝑚𝑠−1

𝑣 𝑦

𝑣=20𝑚𝑠−1

Projectile Motion

𝑣 𝑥

𝑣=20𝑚𝑠−1

𝑣 𝑦

Projectile Motion

Find the vertical and horizontal components of the golf balls velocity if it had an initial velocity of 20ms-1, and angled at 20o to the horizontal.

a) Draw the diagramb) Work out vertical component of velocityc) Work out horizontal component of velocityd) Do your answers make sense?

a)b) c) d) Of course!

Projectile Motion

Find the vertical and horizontal component of a mortar round if it is fired at an angle of 75o to the horizon at a speed of 140ms-1

Projectile Motion

Why did we split up the velocity into horizontal and vertical components? Because gravity only acts on the

vertical component Therefore horizontal component stays

at constant velocity

Projectile Motion

Horizontal Component of Velocity: Use Vertical Component of Velocity: Use the

equations of motion

Vertical Drop

Projectile

Compare the two

Projectile Motion

Horizontal Component of Velocity: Use Vertical Component of Velocity: Use the

equations of motion

Projectile Motion

Golf ball hit had an initial velocity of 20ms-1, and angled at 20o to the horizontal. How far does it go before hitting the ground? (Assume no air resistance)

𝑣=20𝑚𝑠−1

Projectile Motion

Use y-component of velocity. Need to use an equation of motion

Work out v first

Why two answers?

Projectile Motion

Now t.

Projectile Motion

Now use t with the horizontal component of velocity to work out the horizontal distance

Don’t give up your day job if that is as far as you can hit!

Projectile Motion

Summary: Split initial velocity into horizontal and

vertical components Horizontal component uses v=x/t Vertical component uses equations of

motion

Question

Golf ball hit had an initial velocity of 50ms-1, and angled at 35o to the horizontal. How far does it go before hitting the ground? (Assume no air resistance)

𝑣=50𝑚𝑠−1

Questions

Sample – Q5 a & b 2011 – Q 12 and 13

2011 Q12 and 13

Domenic fires a toy cannon, and the projectile leaves the barrel with a velocity of 24 ms-1 at an angle of 37o to the horizontal as shown. Ignore air resistance

2011 Q12 and Q13

How long does it take for the projectile to move from point A to point B?

What is the maximum height of the trajectory?

Projectiles and Air resistance

When you account for air resistance in projectile motion, how does it change the trajectory?

Demo Draw trajectory

Happy Gilmour Golf

After the stunning success of your last project: Angry Shapes, the game designer has come back to you with a fresh project: Happy Gilmour Golf

Chapter 2 – Collisions and circular motion

Momentum

What is momentum? Mass x velocity Units: kgms-1

What is it good for? Analysing collisions or when velocity

has changed

Conservation of momentum

The reason it is so good for analysing collisions is that…

In a closed system, TOTAL MOMENTUM is CONSERVED

Conserved = Stays the same.

Concept question example

Concept Question Example

The man jumps from his boat to the shore.

What happens to the boat?

Momentum

Write down what YOU think happens to the boat.

Why..?

Demo of what just happened

Momentum

Before the man jumps, what is his momentum? (Use a word to describe it)

Before the man jumps, what is the boat’s momentum? (Use a word to describe it)

Before the man jumps, what is the combined TOTAL momentum of the boat and man?

Momentum

When the man is in the air, what is his momentum? (Use a word to describe it)

When the man is in the air, what is the momentum of the boat?

When the man is in the air, what is the combined TOTAL momentum of the boat and the man?

Conservation of Momentum

When driving his Lamborghini home from school, Mr. McGovern doesn’t notice the car that has stopped in front him, and collides with this car. Before the collision, Mr. McGovern was travelling at 15ms-1. After the collision, the two cars stick together as shown in the figure below, and move with the same speeds. Mr. McGovern’s car has a mass of 2000kg, and the other car has a mass of 1500kg.

Figure 1: Before collision only Mr. McGovern’s car is

moving. After collision both cars stick together and move away at the same speed.

Momentum

1) What is the total speed of the two car wreck after the collision.

2) First: Plan how you will do this3) Then, do it!

Questions

Sample Q1a 2012 Q2

How do we relate momentum to other things in motion?

When is momentum useful for calculating stuff?

Collisions When the momentum is changing. What needs to happen for the

momentum of something to change? A force!

So… momentum not helpful when it stays the same

But its helpful when we have a collision, or a change in momentum

How are force and change in momentum related?

ForceChange in momentum

Impulse!

Change in momentum (lamborgini) = final momentum – initial momentum.

Change in momentum = Impulse = F x t

Question

Sample Q6 b

Energy

Types of energy? Two types: Kinetic Potential (stored)

Kinetic Electricity Sound Elastic Gravitational Heat Chemical Elastic Nuclear Light energy Wave

Energy

Place them into kinetic energy or potential energy

Energy

Kinetic Energy = Gravitational potential energy = mgh

Conservation of Energy

Energy can never be created or destroyed, only moved from one form to another.

Energy

A steel ball rolls along a smooth, hard, level surface with a certain speed. It then smoothly rolls up and over the hill shown below. How does its speed at point B after it rolls over the hill compare to its speed at point A before it rolls over the hill?

a. Its speed is significantly less at point B than at point A.

b. Its speed is very nearly the same at point B as at point A.

c. Its speed is slightly greater at point B than at point A.

d. Its speed is much greater at point B than at point A.

e. The information is insufficient to answer the question.

Work is defined as: how much an object energy has changed by.

Eg. A 1kg brick is lifted 1m vertically and placed on a table. How much work has been done?

The work can also be found from the area under a Force-Distance graph

This is especially useful if the force is not a constant force.

Questions

2012 1a & b 2011 Q14 & 15

Work 2012 1a and b

Elastic and inelastic collisions

Elastic collision means that kinetic energy is conserved

Inelastic collision means that kinetic energy is not conserved.

Hang on a minute! How can that be? The energy is still conserved, but it is

transferred to some wasteful form like sound or heat

Questions

Sample Q 1b

Springs: Hooke’s law and elastic potential energy

Normal ExtendedCompressed

Δx Δx

Springs

Demo: What direction is the force from the spring after you extend it and compress it?

Does the force get bigger or smaller the more you compress or extend it?

What could the equation that relates force and extension be?

Springs: Hooke’s Law

k = spring constant (depends on the spring).

Eg, would this spring have a big spring constant or a little spring constant?

Springs

Springs can also be used on the horizontal …

Springs and elastic potential energy

Springs store energy with the equation

Springs

Demo: Sonic Ranger Draw graphs of … Displacement, velocity, acceleration,

kinetic energy, elastic potential energy, gravitational potential energy, total energy

Questions

Sample Question 3a -b 2011 Question 16-20

Circular Motion

Things that travel in a circular motion… Bucket on the end of a string. Moon about the earth Earth about the sun Hammer throw Cyclist in a velodrome Car going around a corner

Circular Motion

Speed = ?? Speed = distance/time Speed = (2πr)/time

Circular motion

What about the car’s velocity? Velocity is changing, because as it goes

around the circle, its direction changes! A changing velocity means … Acceleration! Acceleration means there must be a

force!

Centripetal acceleration

Acceleration in a circle is called “centripetal acceleration”

NOT “centrifugal acceleration”

Substitute in the formula for the speed of an object in circular motion

Centripetal Acceleration

What is the direction of the acceleration?

Velocity

Centripetal Acceleration

Centripetal Acceleration is always towards the centre

What happens if we let go of circular motion?

Flies off at tangent

Question.

A car is travelling around a circular track, and a driver drops his apple core out the window. Litterer! Which direction does it travel as it falls?

Forces that cause circular motion

Tension force Gravity Friction

What direction must these forces be acting in? F = ma So, in the same direction as the centripetal

acceleration Called the centripetal force (NOT centrifugal!)

Questions

Sample Q 2

Example: Circular Motion

1. Calculate the radius of the ball’s path2. Draw all forces acting on the ball3. What is the net force? What is this called4. Calculate the tension force in the string5. How fast is the ball travelling?

Mass = 150g

Do on board

1: The radius

2: Draw the forces on the ball Mass = 150g

Gravity and Tension

Circular Motion

How do we add forces? Head to tail!

Circular Motion

60o FT

Circular Motion

60o FT

Recall… Ball on a ramp

Which direction is the acceleration? Which direction is the net force? What forces add together to give the

net force?

What about a bike on a velodrome wall?

Draw the direction of the total force (the centripetal force)

Draw the forces that make up this total force

Circular Motion

What is the difference between this and the ball that rolls down the ramp?

On the ramp, the total force (and acceleration) is down the ramp. On the velodrome, the total force (and acceleration) is towards the centre

Circular Motion

If on the velodrome, the bike wasn’t moving… what would happen?

Acceleration would be the same as the ball on the ramp and they would roll down the incline!

Circular motion in a vertical plane

Imagine you are in the roller coaster car below, and it travels with a constant speed of 8ms-1 along the track

Circular Motion in a vertical plane

Describe what you feel as you get to point A

Describe what you feel as you get to point B

Lets do the maths… Find the Normal forces on an 80kg

man in the coaster at point A and at point B

The track can be broken into two circular sections, with radii = 10m

10m10m

Do on board (together with slides…)

At point A

– This is the total force on the man Direction=upwards What are the two forces that act on the

man in the coaster at A? Gravity and the Normal Force.

Together these two forces add up to 512N

What is the normal force equal to? 1296N

At point B

– This is the total force on the man. Direction = Downwards. So centripetal force is the same, but in

different direction

Together gravity and the normal force add up to 512N

What is the normal force equal to? 272N

So compare the normal forces acting on the man at the two points

How does this compare to what we feel?

We feel the roller coaster pushing with a bigger force at point A

At point B, it pushes with a smaller force, we feel more “weightless”

Demo: water in the bucket… How to keep the water in the bucket?... What is the minimum speed…?

In order for the water to stay in the bucket (or the people to stay in a roller coaster…), the centripetal acceleration must be equal to, or greater than the acceleration due to gravity

Why? If they have a centripetal acceleration

greater than gravity, they move around the roller coaster faster than they “fall”

Eraser example

Questions

Sample Q 7 2011 Q 4, 5, 6 2011 Q 9, 10, 11

Chapter 3 – Gravity and satellites

Does the earth’s gravity extend as far as …?

Do this as a Think pair share…

To a person standing on earth’s surface? A person who jumped in the air? An aeroplane in the sky? Satellites orbiting the earth? The moon? How come weightless in satellites/space

ships?

Law of gravity

Newton isn’t famous for “discovering gravity”, but for correctly figuring out that the thing that pulls us (and apples) to the surface of the earth, is the same thing that keeps the planets orbiting the sun (and the moon around the earth)

G = 6.67x10-11

Law of Gravity

If I have a mass of 80kg, what is the force of gravity on me?

Using the earth’s mass of 6x1024kg and radius of 6.4x106m

Newton’s Law of Gravity

If And What does at the earth’s surface

Gravitational fields

Using Newton’s law, what happens to earth’s gravitational field as you move further away from it?

It gets smaller

Gravitational Fields

A field is a series of arrows, which show the direction of a certain force

The arrows are the same distance apart and direction because…

Distance apart = strength of field At the earths surface gravity is the

When we zoom back…

As we move out, the arrows are further apart = less gravity

Using and [Mass earth: 6x1024kg ;

Radius:6400km] At… 400km (ISS), g = … 36000km (comm sat), g = …

Something to think about …

8.7ms-2

0.22ms-2

So how do satellites orbit the earth?

There is still gravity there… Newton’s thought experiment

[Draw on board]

Satellites

So, satellites go around the earth, in circular motion

What force keeps them in motion? Gravity What equations can we remember from

circular motion?

Therefore,

Satellites

What do we know about the force of gravity?

Equate the two

What cancels?

Satellites

Whoop de doo basil – what does it all mean?

It doesn’t matter what the mass of the satellite is!

If this wasn’t the case it would be a wee problem… think space walks …

Space walks…

Kepler’s Law

In a circular motion,

So equation from last page becomes Working on the board

Or This is similar to , but we have the time

period instead of the velocity

Satellites

Eg, sometimes you might want to know the time period of a satellite (how many hours it takes to go around the earth) and sometimes you want to know what the orbiting speed is.

Geostationary Satellites

A geostationary satellite is one that has an orbiting period exactly equal to one day (24 hours in earth’s case)

Example Questions

1) Calculate the orbiting radius of a geostationary orbit

2) Calculate the orbiting time of the ISS [400km height]

Question 2012 Q8 a

Note… Tricky little question…

Question Sample Q8a-c

Questions

Looking at Satellites

And iridium flares Who has seen a satellite going across? http://www.heavens-above.com http://spotthestation.nasa.gov/

Energy changes in gravity fields

Graphs

Apparent weight and weightlessness

ISS orbits at 400km (g=8.7ms-2) But …

How can they be weightless?

If a space ship travelled into deep space, where g=0ms-2 , then the astronauts would be truly weightless

Astronauts in “near earth” orbits “appear weightless”

When else do you feel reduced weight or weightlessness?

Getting to the top of a lift Starting the lift (going down) Driving over the top of a small hill Falling

Apparent Weight

Our apparent weight is equal to the normal force acting on us

At the bottom of a roller coaster we feel heavy (large normal force)

At the top we feel light (low normal force)

Vomit Comet…

Apparent Weightlessness

When a space shuttle is orbiting the earth, the force of gravity is = to the centripetal force

There is no normal force! Astronauts are basically in a continual

free fall around the earth Therefore appear to be weightless! But why don’t they crash into earth? They are moving sideways as well

Apparent Weightlessness

Its like the astronauts are at the top of a roller coaster loop-to-loop, with a slow enough force that they feel weightless. But their entire orbit around the earth feels like this!

Questions

Sample Q 4 a-c 2012 Q8, b

Kerbal Space Program

Revised Concept Map

Make a concept map with Forces in the middle.

Use concept map to predict what type of questions are being asked

And do some questions for revision…

Some questions (from exams)

Finish remaining questions from Sample, 2012, and 2011 in the “Motion” section

2012: Q1a-d, 6a-b, 7a-c 2011: 1,2,3, 21-23

Electronics and Photonics

Topics

Review of electronics Voltage dividers and thermistors Diodes Amplification Photonics systems and modulation

Electronics Review

Symbols Voltage Current Resistance Ohms Law Power Series Parallel

Electrical SymbolsDevice Symbol Device Symbol

Wires crossed (not joined)

Wires joined Battery of cells

Resistor or other load

AC supply

Resistor Ammeter

Filament Lamp Voltmeter

Diode DC Supply

Earth or ground

Switch

Voltage

The amount of energy supplied by the battery per coulomb.

It is effectively “used up” by components of a circuit

Measured in Volts A voltmeter must be in parallel with a

component Also called “potential difference”

Current

How many coulombs per second. Total current depends on the components

of the circuit: They “draw” current out of the battery

Measured in Amps Ammeter must be in series Current flows from + to – in a circuit. Or

from high voltage to low voltage (although the electrons flow the opposite way)

Revision of Electronics 1

Resistance

All electrical components have a resistance

for an Ohmic resistor

Ohm’s Law

An Ohmic resistor has constant resistance over it when different voltages are applied over it

Has a straight line graph for V-I

P=VI Can be calculated for each electrical

component (power used) Or calculated for battery (power

supplied) Measured in Watts (W)

Series Circuits

This is an example of light bulbs in series…

Series

In a series part of the circuit… Current doesn’t change Voltage is used up

Series

Eg, Find the total resistance of these bulbs

100Ω 100Ω 100Ω

Series

Find the total resistance of these sets of bulbs

100Ω 50Ω 30Ω

20Ω 50Ω 30Ω

Parallel Circuits

This is an example of bulbs in parallel…

Parallel

In a parallel part of the circuit… Current splits up (but not necessarily in

half) Voltage is the same in each arm of the

parallel

Parallel

Find the total resistance

Parallel

Find the total resistance

Combining Series and Parallel…

4Ω 4Ω

Revision Prac. Similar to the question in sample. Set up, which bulb is the brightest for

maybe three different circuits

Combining series and parallel

Sample Q9a-c [Together] 2012 A2 Q1 2011 A2 Q1-4

Voltage Dividers

In the following circuit, what would the voltage be, measured over…

Bulb A Bulb B?

Voltage Dividers

Yes, in a series circuit, the voltage is divided between the components

Voltage Dividers

What about in the following circuit. What is the voltage over

Bulb A Bulb B

Voltage Dividers

What about now? Bulb A Bulb B

Voltage Dividers

An now… Bulb A Bulb B

Voltage Divider Prac

Make a voltage divider Make one with a variable resistor

Voltage Dividers

What is a general rule for how the voltage is divided in a series circuit?

Voltage Dividers

What are they good for? Demo: Variable resistor Room in the book to draw the circuit

diagram.

Voltage Divider

If we swap the variable resistor from before with a thermistor or LDR, we can get a cool “control circuit”

Voltage Divider

Thermistor: Is a resistor, whose resistance changes depending on its temperature

Symbol: Graph (Board)

Voltage Divider

LDR: Light Dependant Resistor. A resistor whose resistance depends on

the amount of light falling on it. Symbol:

Voltage Divider

Using a thermistor (or LDR), we can make a control circuit to control a fan (or air conditioner):

Circuit diagram When the temperature rises, the

resistance of the thermistor decreases.

Voltage Divider

When the temperature rises, the resistance of the thermistor decreases.

The voltage increases in the output. When the voltage in the output reads a

certain amount, the fan circuit will turn on!

Voltage Divider Questions

Samp. Q 13 2011 – A2 – Q 5 & 6

Diodes

Quick Prac – Diodes. Increase voltage. Reverse Bias. Make graph

Diodes

Diodes are a non-ohmic device They only allow current to flow in one

direction. This is called “forward bias” A diode connect in “reverse bias” will

allow no current to flow Diode symbol:

Diodes

Threshold Voltage. After a diode reaches its threshold voltage, it conducts like a wire: resistance free

Note: You cannot connect a diode to a circuit without a resistor! It will short circuit and explode…

Diode Graph

Example Questions

Consider the following circuit. The diode has a threshold voltage of 3V.

Example

1. Will the bulb glow??2. How could you make it glow?3. Assume the diode is now the correct

way around. 4. What is the voltage used by the diode?5. What is the voltage used by the bulb?6. What is the current measured at point

A?7. What is the power used by the bulb?

Diodes

Different types of diodes include Light Emitting Diode (LED), and photo diode.

Both still have the same characteristics as a diode

Question

Sample Q10 a-b 2012 A2 Q2

Amplification

A typical electrical signal, that is transmitting sound, might look like this…

Amplification

Draw what it might look like if it was amplified 2x…

This is known as the “gain”

Amplification

Amplifiers can de-amplify. Amplifiers can be inverting as well.

Draw the signal if it was amplified with an inverting amplifier with gain of -5

Amplification

A typical voltage in/ voltage out graph looks like …

The gain is the slope of the graph. What is the gain of this graph? Is it

inverting/non inverting?

Amplification

What is the gain of this graph? Is it inverting/non inverting?

Amplification

Clipping can occur, if you attempt to amplify a signal larger than the amplifier can supply

This is called saturation of the amplifier The saturation voltage is the largest

that the amplifier can output If the signal has structure, this can

result in a distortion of the signal (Draw on board)

Amplification

Amplification achieved with a transistor

Amplification

More readily done today with an IC (integrated circuit) that has many transistors/resistors and capacitors built into it

Prac: Amplification

Demo / prac

I'm looking for an opamp similar to a 5532 that I can operate using a> single 9 volt battery for the power supply. I use 5532's for general> audio circuits but my datasheet recommends a minimum supply voltage of> 10 volts for this device.>> Anyone know of a good low voltage opamp for audio aplications? BTW, a> deviced that is second sourced would be nice.

It depends a bit on what you're trying to do. 9v is a bit of an awkwardvoltage because many of the newer opamps are designed for the 3v or 5v rangeand won't go up to 9v; the older ones, as you know, are often designed forat least +/-5v, that is, 10v single supply.

Don't fret too much about the rated supply voltage. You can actually getdecent audio performance out of even those ones rated for at least 10v, on a9v battery. It's one of those things where the manufacturer won't promiseit but hundreds of thousands of audio devices have proven it does work.

The TL062 is probably the most common opamp that I encounter for 9v audiowork. It has the advantage of very low supply current. It is, however,very noisy and has crappy frequency response - that's the tradeoff. Forbetter sound at the expense of more supply current, the TL072 is a goodopamp. The LM358 has also been widely used for 9v audio, although it doeshave some shortcomings.

Note that both the TL062 and TL072 have improved versions, the TLE2062 andTLE2072 respectively, with better specs. The TLE2072 uses 1.8mA perchannel, is rated for supply voltages as low as 4.5v (single supply!), andhas a 10MHz gain bandwidth. I've used it in a number of battery-poweredaudio applications with good success.

As GregS points out, the OPA2134 is a truly excellent opamp, and is ratedfor 5v single supply. It does consume 3 times the current of the TLE2072,though.

Questions

Sample 11 a-b 2012 A2 Q4 2011 A2 Q11, 12

Photonics

Photonics is the transfer of information or signals using light.

We have it because electrical wire could only transfer one phone call per wire

Fibre optics can transfer up to 1000 phone calls per fibre cable!

Plus, its cheaper! Electrical cables are made from copper. Fibre is made from glass (silica), which is made from sand.

How might you use light to transfer information

Morse code? What would we need? Something to produce the light Something to direct the lights travel Something to receive the light and to

“translate it”

A photonics system

Diagram

Has encoder/modulator Emitter Transfer medium Receiver Demodulator

Emitters

LED (Light emitting diodes) Laser Diodes – These are LED’s with a

laser cavity.

Receivers

LDR – Light dependant resistors Photodiodes – Light dependant diodes

LDR prac

Modulation

Why How Modulation and demodulation of the

carrier wave.

Some sort of prac

La Trobe. (Find out specifics)

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