Experiment q1 electron charge to mass ratio abstract the ratio em for electrons is determined by measuring the radius of curvature of the path followed by electrons of known velocity as they move in a known magnetic field. A particle of mass m and charge e moving in a magnetic induction field b will. With the help of his experiments, he derived a formula for the calculation of charge to mass ratio of the electron. The importance of the mass to charge ratio, according. This experiment investigates the path of an electron in a magnetic field. Measuring separately the electric charge \e\ and the rest mass \m\ of an electron is a difficult task because both quantities are extremely small \e\ 1. Table i electron charge and mass quantity symbol value units mass me 9. This is a variation of the original experiment carried out by j. Thomson, cathode rays and the electron introduction. Ratio of mass to charge for an electron goal to build a physical model of how an electron behaves in the presence of electric, magnetic and gravitational fields. When these two coils are set side by side and the distance between them is r as shown in figure 2, they generate a nearly uniform magnetic field to the center point c.
Pdf charge to mass ratio experiment cody johnson academia. This experiment was one of the first experiments to attempt to find the charge or mass of an electron. Experimental setup for charge to mass ratio determination. The charge to mass ratio of the electron 1 introduction in this exercise we will measure the charge to mass ratio of the electron by accelerating an electron beam through a known potential and measuring the radius of curvature of the beam in a known magnetic. The first is the experiment of joseph john thomson, who first demonstrated that atoms are actually composed of aggregates of charged particles. Measurement of chargetomass em ratio for the electron. Includes teachers notes and typical experiment results.
Students will observe the interaction between a magnetic field and an electron beam, and measure the charge to mass ratio of the electron. Measurement of charge to mass em ratio for the electron experiment objectives. Motivation and history of the first em measurement consequences thomsons experiment the physics behind the experiment. Name the 2 forces that are equated in order to derive the charge to mass ratio relationship. To experimentally determine the electron charge to mass ratio overview in this experiment, you will measure em, the ratio of the electrons charge e to its mass m. Added lasers for better accuracy with beam radius, one trial as with the brighter green. Equipment elwe em tube, elwe helmholtz coils, elwe 4 voltage power supply, safety.
Mass to charge ratio introduction just as moving charges induce magnetic. From the empirical data obtained, we arrive at a value for the ratio of charge to mass of an electron. Use this physical model to design an experiment to measure the charge to mass ratio of an electron as well as the charge on an electron. The charge to mass ratio of an electron was studied using an electron beam tube and two helmholtz coils. Thomson discovered the electron by measuring the charge to mass ratio of cathode rays actually, streams of electrons, with charge q and mass m as follows. Thompson was able to observe the motion of single electrons in electric and magnetic fields, and so determine the ratio of the electrons charge, e, to its mass, m. Describe or make a rough sketch of the path of an electron traveling into a region with a constant bfield. This is the same experiment that was conducted by j. Thomson measured the ratio of charge to mass em of these corpuscles of which the rays were composed. A beam of electrons is accelerated through a known potential, so the velocity of the electrons is known. The setup consists of an evacuated except for a low pressure of he gas cathode ray tube which produces a beam of electrons of variable energy. The beam is visible because it excites the lowpressure gas contained in the tube. The magnetic field generated by a single loop charged particle in constant magnetic field. Introduction and theory around the turn o f the century, two dramatic experiments established the existence of the electron, a charged particle that is very much smaller than an atom in size and in mass.
In the present experiment a beam of electrons is accelerated through a known potential, so the velocity of the electrons is known. Charge and mass of the electron michigan state university. Finally, this allows the charge to mass ratio to be represented by the formula. Experiment 6 the chargetomass ratio of the electron.
The mass to charge ratio mq is a physical quantity that is most widely used in the electrodynamics of charged particles, e. Introduction in this lab you will repeat a classic experiment which was first performed by j. Lab 5 electron chargetomass ratio university of virginia. The velocity will change direction but not magnitude.
P31220 lab 1 charge to mass ratio of the electron purpose. Chargetomass ratio for the electron u of t physics. Experimental determination of em using thomsans method. The set up of the apparatus is included with this report. For electrons or any given kind of particle the left hand side is a constant. Mass to charge ratio introduction just as moving charges induce magnetic elds, as seen in the previous lab, charged particles moving in the presence of a magnetic eld feel a magnetic force. Electron charge to mass ratio em university of alabama. The objective of this experiment is to determine the electrons charge to mass ratio em. Thompson investigating the cyclotronic motion of an electron beam. A pair of helmholtz coils produces a uniform and measurable magnetic field at right angles to the electron. It was found that the electron charge to mass ratio when the voltage was held constant. The charge to mass ratio system reproduces one version of thomsons landmark experiment, providing an accurate measurement of the charge to mass ratio of the electron.
Electron charge to mass ratio matthew norton, chris bush. Well do his experiment, with a somewhat modified apparatus. In measuring the charge to mass ratio eme in this experiment, the apparatus is arranged so that the force will be perpendicular to v and b. They are known to much higher accuracy than we can hope to measure in our experiments and, therefore, they will be considered to be exact. Thomsons experiment and the charge to mass ratio of the electron. References reese, university physics, brookscole, 2000. The charge to mass ratio of the electron is given by.
Determination of particle charge to mass ratio distribution in electrostatic applications. He conducted a series of revolutionary experiments with cathode ray tubes. While the concept of atom dates back to the ancient greeks, the current picture of an atom is. Experiment q1 electron chargetomass ratio abstract. Then the charged particle will move in a curved path in a plane perpendicular to b. Hb 102008 charge to mass ratio of electron lab 11 3 to nd an expression for vin terms of quantities that can be measured, we note that the kinetic energy imparted to an electron within the tube is given by evwhere vis the potential di erence through which the electrons have been accelerated and is the voltage between the cathode and the anode. The electron chargetomass ratio equipment the experiment and. Castle department of electrical and computer engineering university of western ontario phone.
It appears in the scientific fields of electron microscopy, cathode ray tubes, accelerator physics, nuclear physics, auger electron spectroscopy, cosmology and mass spectrometry. Charge to mass ratio for the electron introduction this is a variation of the original experiment carried out by j. Determine an expression for the constant cin terms of measureable quantities and the charge to mass ratio em. The clever experiment exploits two ideas that were known about the interaction between electromagnetic fields and charged particles. The em apparatus electron charge to mass ratio provides a simple method for measuring em, the charge to mass ratio of the electron. In this experiment, you will perform a modification of thomsons original work. To meet this objective we will use a vacuum tube capable of producing a visible beam of electrons as shown in figure 1. Fundamental physics experiments charge to mass ratio of. Charge to mass ratio for electrons introduction in this experiment you will study the application of several of the physical laws that you were taught in sophomore physics to a system in which electrons are injected into a fairly uniform, constant magnetic field.
At the turn of the century several crucial experiments were performed to demonstrate the atomic structure of matter. Fortunately, the ratio of these two fundamental constants can be determined easily and precisely from the radius of. You should be able to write this equation in the form r c jbj 1 where cis a constant. Given that it is also possible to perform a measurement of. After the charge to mass ratio was found, all someone would have to do was to find the charge or mass of an electron, and the other value would be known. Charge to mass ratio of electron ohio wesleyan university. Charge to mass ratio of the electron julia velkovska september 2006 1. Substitute 4 into 3, we can get the charge to mass ratio of the electron. Thompson to measure the charge to mass ratio in the early 20th century. Experiment 6 the chargetomass ratio of the electron ucla. In this experiment you will measure em, the ratio of charge e to mass m of the electron. This experiment measures em, the charge to mass ratio of the electron. Tuggle ph 235001, group 4 18 january 2010 abstract we have repeated with some modi. By measuring the radius of curvature of the electrons path as a.