Subversive Physics:

Subversive Physics: Covering today’s outcomes with today’s Physics

Momentum and Magnetic Fields 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.

Momentum and Magnetic Fields 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.

Momentum and Magnetic Fields 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.

Momentum and Magnetic Fields Today’s Physics: Bubble Chambers So let’s see what we can figure out. First, the rules of the ‘game’. • 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 -1 5) 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.

Momentum and Magnetic Fields So let’s play… Since the interactions must take place “downstream”, the particles must be moving toward the top of the page. • Up • Down Here we see the kaon ‘beam’ Which way are they traveling?

Momentum and Magnetic Fields What is the direction of the magnetic field? • Into the page. • Out of the page. • To the right. • To the left The negative kaons are pushed to the left. thumb Back of hand

Momentum and Magnetic Fields The spirals are caused by an interaction between a particle and something in the liquid. What are the particles hitting? • Protons • Electrons • c) Neutrons The particles must be losing energy since the tracks spiral. They must be charged. The tracks spiral to the left.

Momentum and Magnetic Fields A collision happens at A. One particle travels to the right and another to the left. Which answer summarizes what happened at A? The path on the left is curved. The charge of the kaon must be conserved. A

Momentum and Magnetic Fields 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? • It was moving too fast • It was moving into the page • It was stationary The chamber is filled with liquid hydrogen. There are lots of stationary positive protons. A

Momentum and Magnetic Fields Which of the tracks from A shows the particle with the smaller momentum? F = qvB p α r So the smaller the radius (the more curved the path) the smaller the momentum. A

Momentum and Magnetic Fields How many particles were created in the collision at A. • 2 • 3 • At least 2 • At least 3 B Notice B There may have been a neutral particle produced at A. A

Momentum and Magnetic Fields What happened at B? The total charge after the interaction is neutral, so the total charge beforehand must be neutral • The neutral particle • Collides with a neutral particle • Collides with a positive particle • Decays into a positive and a negative particle • Decays into two negative particles x x B The hydrogen contains only protons and electrons x We see that two charged particles are produced. One is positive and one is negative. A

Momentum and Magnetic Fields 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. For more examples and questions check out: http://epweb2.ph.bham.ac.uk/user/watkins/seeweb/Bubble.htm

Constant Velocity and Relativity 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

Constant Velocity and Relativity 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!

Where Are You? 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… • 2154 km from Vancouver • 1879 km away from Churchill Falls, Labrador. • 2464 km away from Charlottetown, PEI. With your map, we can find out where you are located. But first, we’ll need a scale.

Where Are You? 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 3.25cm=1000km 1 cm = 308 km Every cm on the map means 308 km on the Earth’s surface.

Where Are You? • You are 2154 km from Vancouver So if we’re 2154km away that’s… You are 6.99 cm away from Vancouver on the map. But that could be in any direction. So let’s draw a circle of radius 6.99 cm whose centre is Vancouver.

Where are we? here here here You could be…

Where Are You? 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. You are 6.10 cm away from Churchill Falls on the map. But that could be in any direction. So let’s draw a circle of radius 6.10 cm whose centre is Churchill Falls.

here here Now you could be…

Where Are You? 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. You are 8.0 cm away from Charlottetown on the map. But that could be in any direction. So let’s draw a circle of radius 8.0 cm whose centre is Charlottetown.

You are here!

There You Are! You were in Churchill, Manitoba. We used distances from three satellites to discover your position. Now the question becomes, How do the satellites measure those distances? We know that GPS satellites orbit the Earth at a height of 20 200 km. The satellite sends a TIME signal to the receiver indicating the time the signal was sent. 20200 km The receiver measures the time when it receives the signal.

There You Are! How do the satellites measure those distances? The difference in time is used, with the speed of the signal to calculate the distance between the receiver and the satellite. 3.0 x 105km/s x 0.07s = 21 000 km 20200 km 21000km 5741 km Now, using Pythagoras’ Theorem we can find the distance between the two cities.

When You Are? 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 Relativistic Effects That time elapses faster when you’re high above the ground That time elapses slower when you’re moving really fast

Working It Out 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 = 0.06821s Satellite B is 20 200km above Iqaluit, NWT. t = 0.06764s Satellite C is 20 200km above Thunder Bay, Ont. t = 0.06758s Find 1) The distance between the satellite and the receiver. 2) The distance between the city and the receiver. 3) Where the receiver is.

Working It Out A) B) C)

The Challenge of Quantum Reality 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 Challenge of Quantum Reality 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 Challenge of Quantum Reality 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 Challenge of Quantum Reality 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. But now…

The Challenge of Quantum Reality 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… But now… they must be considered as waves as well.

The Challenge of Quantum Reality 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.

The Challenge of Quantum Reality 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.

Subversive Physics: