Covering today’s outcomes with today’s Physics

Today’s Outcomes in Physics 12

326-3: apply quantitatively the laws of conservation of momentum to two-dimensional collisions and explosions.

328-5: analyse, qualitatively and quantitatively, the forces acting on a moving charge and on an electric current in a uniform magnetic field.

Today’s Physics

We are a long way from the idea that protons, neutrons and electrons are the fundamental particles in nature. Physicists now know that there are a multitude of sub-atomic particles. They can observe these particles in a bubble chamber.

A bubble chamber is a detector filled with a liquid close to its boiling point (superheated), where the ionizing particles' trajectories materialize in the form of tracks made of bubbles.

Today’s Physics: Bubble Chambers Just like the salt produced trails showing its path, particles will initiate boiling by ionizing the atoms in the liquid as they pass through the liquid. These trails, coupled with some Grade 12 Physics enable us to observe sub-atomic particles.

Today’s Physics: Bubble Chambers So let’s see what we can figure out. First, the rules

of the ‘game’.

1) The photos we will use are from CERN’s BC site:http://teachers.web.cern.ch/teachers/archiv/HST2005/bubble_chambers/BCwebsite/

index.htm

2) The chamber is filled with liquid hydrogen. Negative kaon particles (K-) were shot into it. These particles can hit the protons or electrons of the hydrogen or, of course, simply pass right through them.3) The trails are the result of a charged particle causing

the hydrogen to boil.4) Charge and momentum are conserved. The charge is either +1 or -15) The constant magnetic field will exert of force on the moving charged particle whose magnitude is found with F = qvB and whose direction is found with the right-hand rules.

So let’s play…

Here we see the kaon ‘beam’Which way are they traveling?

Since the interactions must take place “downstream”, the particles must be moving toward the top of the page.

a) Up

b) Down

What is the direction of the magnetic field?a) Into the page.

b) Out of the page.

a) To the right.

b) To the left

The negative kaons are pushed to the left.

Back of hand

The spirals are caused by an interaction between a particle and something in the liquid. What are the particles hitting?

a) Protons

b) Electrons c) Neutrons

The particles must be losing energy since the tracks spiral. They must be charged.

The tracks spiral to the left.

A collision happens at A. One particle travels to the right and another to the left. Which answer summarizes what happened at A?

The trail on the left

The trail on the right

a) A negative particle

A positive particle

b) A positive particle

A negative particle

c) A negative particle

A negative particle

d) A positive particle

A positive particle

The path on the left is curved.

The charge of the kaon must be conserved.

In the interaction at A, a kaon produced a positive and a negative charge. How can a negative particle produce a positive and a negative charge?The kaon must have interacted with a positive charge. Why didn’t we see the positive charge before the collision?a) It was moving too

fastb) It was moving into

the pagec) It was stationary

The chamber is filled with liquid hydrogen. There are lots of stationary positive protons.

Which of the tracks from A shows the particle with the smaller momentum?

F = qvB

mvqBr

p α rSo the smaller the radius (the more curved the path) the smaller the momentum.

r

2mv Fc

rmvqB

How many particles were created in the collision at A.

a) 2b) 3c) At least 2d) At least 3

Notice B

There may have been a neutral particle produced at A.

What happened at B?

The neutral particle

a)Collides with a neutral particleb)Collides with a positive particlec)Decays into a positive and a negative particled)Decays into two negative particlesWe see that two charged

particles are produced. One is positive and one is negative.

The total charge after the interaction is neutral, so the total charge beforehand must be neutral

The hydrogen contains only protons and electrons

In using the bubble chamber diagram, students have used the concepts of the conservation of momentum in 2D and their right hand rules. They have also related the force on a charge moving in a magnetic field to its momentum.

http://epweb2.ph.bham.ac.uk/user/watkins/seeweb/Bubble.htm

For more examples and questions check out:

Today’s Outcomes in Physics 11

325-2: analyse graphically and mathematically the relationship among displacement, velocity and time

325-7: identify the frame of reference for a given motion

Today’s Outcomes in Science 10 325-1, 212-7, 325-2 : using linear experimentation with appropriate

technologies, analyse graphically and quantitatively the relationship among distance, time, and speed and the relationship among position, displacement, time, and velocity

Today’s Physics

GPS is everywhere. It is estimated that every day 1 billion people use this technology: farmers, skiers, police, treasure-hunters and surely Physics teachers!

What is it based on?

Relativity of course!

2154 km from Vancouver1879 km away from Churchill Falls, Labrador.2464 km away from Charlottetown, PEI.

So let’s model how GPS works.

Your GPS receiver has picked up signals from three different satellites. One satellite sent the signal when it was above Vancouver, another went it was above Churchill Falls, and the third when it was above Charlottetown. The signals tell us that you are…

With your map, we can find out where you are located.But first, we’ll need a scale.

A scale resizes the diagram. In this diagram a line is drawn to represent 1000km. How long, in centimeters, is this line?

What is the value of 1 cm on the map?This means that

_______ ______ 3.25 3.25

3.25 cm = 1000 km

1 cm = 308 km

Every cm on the map means 308 km on the Earth’s surface.

You are 2154 km from Vancouver

So if we’re 2154km away that’s…

cmkmcmkm 99.6

30812154

You could be…

We see that there are three locations on this map 2154 km away from Vancouver. (There are lots of other locations that distance as well but we know we’re somewhere on the map.)

We need to narrow this down. We also know you are

1879 km away from Churchill Falls, Labrador.

cmkmcmkm 10.6

30811879

Now you could be…

here

here

Well we’re not in the Northwest Territories! We’re either in Sandy Lake, Ontario or Churchill, Manitoba.

We also know that you’re

2464 km away from Charlottetown, PEI.

cmkmcmkm 0.8

30812464

You are here!

You were in Churchill, Manitoba. We used distances from three satellites to discover your position. Now the question becomes,

We know that GPS satellites orbit the Earth at a height of 20 200 km.

2020

0 km

The satellite sends a TIME signal to the receiver indicating the time the signal was sent.The receiver measures the time when it receives the signal.

How do the satellites measure those distances?

The difference in time

How do the satellites measure those distances?

is used, with the speed of the signal

to calculate the distancebetween the receiver and the satellite.

2020

0 km

21 00

0

km

Now, using Pythagoras’ Theorem we can find the distance between the two cities.

5741 km

kmd

kmkmd5741

)20200(21000 22

So GPS is all about WHEN not really about WHERE!The timing of these devices needs to be very precise. Therefore they must take into account

That time elapses faster when you’re high above the ground

That time elapses slower when you’re moving really fast

We now know enough to work this through completely. Three satellites have given your receiver this information:

Satellite A is 20 200km above Fort McMurray, Alberta. t = 0.06821sSatellite B is 20 200km above Iqaluit, NWT. t = 0.06764sSatellite C is 20 200km above Thunder Bay, Ont. t = 0.06758s

1) The distance between the satellite and the receiver.

2) The distance between the city and the receiver.

3) Where the receiver is.

Find

cmkmcmkm

kmdkmkmd

kmskms

61.1030813270

32702020020463

20463/30000006821.022

A)

cmkmcmkm

kmdkmkmd

kmskms

27.6308

11930

19302020020292

20292/30000006764.022

cmkmcmkm

kmdkmkmd

kmskms

62.530811731

17312020020274

20274/30000006758.022

B)

C)

Today’s Outcomes in Physics 12

327-11: summarize the evidence for the wave and particle models of light

115-7 explain how scientific knowledge evolves as new evidence comes to light and as laws and theories are tested and subsequently restricted, revised or replaced.

The video explores the fundamental proof that light is a wave: Young’s double slit experiment.

This shows that light cancels itself out as only a wave can.

The bright spots or fringes show the constructive interference whereas the dark spots show destructive interference

The video then explores the results when “particles” like electrons or atoms or molecules are fired at the double slit.

This same pattern shows that the electrons are cancelling themselves out!!

There is a high probability that the electrons will hit in the “bright fringes” and a low probability that they will hit in the “dark fringes”.

The double slit experiment shows that light is a wave but it also shows that particles act like waves. The idea of what matter is must be changed!

Particles…

For hundreds of years were considered localized quantities of matter. They are in one spot but not another.

The double slit experiment shows that light is a wave but it also shows that particles act like waves. The idea of what matter is must be changed!

Particles…

For hundreds of years were considered localized quantities of matter. They are in one spot but not another.

The double slit experiment shows that light is a wave but it also shows that particles act like waves. The idea of what matter is must be changed!

Particles…

they must be considered as waves as well.

And this reality gets crazier…

When physicists fire one electron at a time, the interference pattern is still formed

When physicists try to measure which slit the single electrons pass through, the interference pattern is destroyed. The electrons act as if they are localized once more. When physicists turn the intensity of the light down (so that one photon at a time hits the double slit) the light hits the screen as a series of discrete bundles- photons. The interference pattern builds up over time like it did with the electrons.

And this reality gets crazier…

So clearly, light is a wave (double slit pattern) unless the intensity is really low then it acts like a localized particle.

And equally clear, is the fact that electrons are localized particles until we turn our backs on them then they act like a wave.