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\bullet Bubble chamber, I. Certain types of bubble chambers are filled with liquid hydrogen. When a particle (such as an electron or a proton) passes through the liquid, it leaves a track of bubbles, which can be photographed to show the path of the particle. The apparatus is immersed in a known magnetic field, which causes the particle to curve. Figure 20.77 is a trace of a bubble chamber image showing the path of an electron. (a) How could you determine the sign of the charge of a particle from a photograph of its path? (b) How can physicists determine the momentum and the speed of this electron by using measurements made on the photograph, given that the magnetic field is known and is perpendicular to the plane of the figure? (c) The electron is obviously spiraling into smaller and smaller circles. What properties of the electron must be changing to cause this behavior? Why does this happen? (d) What would be the path of a neutron in a bubble chamber? Why?

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a) If the charged particle enters a magnetic field and the particle is negative, then the particlen moves clockwise in a circular orbit. If the particle is positive, then the particle movescounterclockwise.b) $\frac{B q v}{m}$c) velocityd) When a neutron enters a bubble chamber it travels a distance of approximately 3.5 $\mathrm{cm}$ anddecays. Since a neutron is not a charged particle, no traces are found.

Physics 101 Mechanics

Physics 102 Electricity and Magnetism

Chapter 20

Magnetic Field and Magnetic Force

Motion Along a Straight Line

Motion in 2d or 3d

Electric Charge and Electric Field

Gauss's Law

Current, Resistance, and Electromotive Force

Direct-Current Circuits

Magnetic Field and Magnetic Forces

Sources of Magnetic field

Electromagnetic Induction

Inductance

Simon Fraser University

University of Sheffield

McMaster University

Lectures

18:38

In physics, electric flux is a measure of the quantity of electric charge passing through a surface. It is used in the study of electromagnetic radiation. The SI unit of electric flux is the weber (symbol: Wb). The electric flux through a surface is calculated by dividing the electric charge passing through the surface by the area of the surface, and multiplying by the permittivity of free space (the permittivity of vacuum is used in the case of a vacuum). The electric flux through a closed surface is zero, by Gauss's law.

04:28

A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude (or strength); as such it is a vector field. The term is used for two distinct but closely related fields denoted by the symbols B and H. The term "magnetic field" is often used to refer to the B field. In a vacuum, B and H are the same, whereas in a material medium, B is a component of H. In the latter case, H is the "magnetic field strength", and B is the "magnetic flux".

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so for party the direction of the curvature. Um, rather, we can look at the path of a particle and see the charge. Um, and the question and question Rather part of the question is asking us how we do that. So the direction of the curvature of the path tells us the direction of the force on the charge. Now, if this is the same as the right hand direction, if this is these same as the right hand to rule direction Um, the particle is positive. Q is greater than zero cool ums again. This would be the right hand direction for velocity and magnitude vectors. So again for weaken, say velocity and thank you over if its opposite We, of course, know that is that the charge is negative. So the charge would be less than 00 Cool arms for part B is asking us Well, what would like, look rather what ah would be be able to find the velocity from a photograph so we can say that M V equals the absolute value of the charge. Times are times be Now here are would be the radius of the curvature and be with me the again the magnitude of the magnetic field. However, from the photograph eso from photograph our can be measured. The radius of the curvature of the past of the path can be measured and from the photograph. If we have this and we have the ah charge on the magnetic field, we confined the momentum. Momentum can then be found. And once we have momentum, if we're dealing with a proton or a lecture on or an Alfa particle most of the particles that we deal with we know the mass. So if the massive known ah, we can say the can be calculated, so that would be for partly for part. See, now we know that if we just were to manipulate this equation a bit, we have our equaling and the divided by to be, um, and here we know that the only thing that would slow down the radius of curvature would be if the electron itself was slowing down. So if electron rather, we could say electron is slowing down, which causes are to decrease, we can say that the election loses kinetic energy as it moves through the liquid. So is the moves of the liquid. The electron is slowing down, which causes the radius of curvature to in Crete to decrease, which means that it's going too slowly. Ah, you know, make smaller and smaller circles, of course. And then, given this that means that the electron, the energy of the the actual total energy of the electron decreases. And it's actually losing kinetic energy to the liquid as it moves through the liquid. And then, lastly for a part D if we wanted to identify a neutron, a neutron has no charge, and this is kind of is this is very convenient. So if a neutron has no charge, um, that means that the magnetic field exerts rather, we consider the magnet field cannot exert a force on an UN charged particle s o. Therefore here the neutron will move in a straight line. And that's how you would be able to tell it's a neutron. Because if it's not being affected by any magnet magnetic fields and it's simply moving in a straight line and not curving, we can immediately tell that the particle is going to be a neutron. That is the end of the solution. Thank you for watching

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