Question

Finding the charge to mass (e/m) ratio of the electron Often in physics, we look for ways to find fundamental physical constants. From the set-up demonstrated in class, we are able to find a monumental combination of two physical constants-the charge of an electron (e) and the mass of an electron (m). Since the charge of an electron (e) is well known through other experiments, we will use the ratio of charge to mass to find the mass of an electron One way to find the charge to mass (e/m) ratio of the electron is to analyze the motion of electrons moving in a magnetic field. How are moving charges impacted by a strong constant magnetic field? A cathode ray tube (CRT) was mounted between a set of Helmholtz coils which produce the strong magnetic field. The cathode ray tube (CRT) acts like an "electron gun." Shown below is a diagram of the inside of a CRT electricity passes from the cathode to the anode a small bit of electricity passes through the hole in the anode cathode anode phophor coating There are two parallel plates shown with the negative plate on the left and the positive plate on the right. The electrons start at rest at the negative plate and are accelerated through the electric field created by the parallel plates. The positive plate has a small hole that allows the beam of electrons to emerge after being accelerated a) f the parallel plates were charged to a voltage of (360 t 40)V, how fast are the emerging electrons traveling? Symbolically solve for the velocity in terms of e, AV and m After the electron beam "warmed up" and we saw a straight line of accelerated electrons, we put a current of (2.1 ± 0.2)Amps through the Helmholtz coils. Each coil has exactly 130 loops. Each coil has a radius of (15 1)cm and the distance between the coils is equal to the radius. The electron beam is located at r/2 from each coil The on-axis strength of the magnetic field from a single loop of a wire is given as: 3/2 Here, R is the radius of the loop, I is the current through the loop and x is the distance away from the loop. b) What is the strength of the magnetic field caused by the Helmholtz coils acting on the electron beam? Symbolically solve for Btotal in terms of the number of turns on each coil N, I, R and any other relevant physical constants. Once there was current running through the coils, the once straight electron beam was observed to curve into a circle of radius (5.2 ± 0.5)cm. c) Write an expression for the sum of the forces on an electron traveling through the magnetic fi lel. d) Symbolically solve for the charge to mass (e/m) ratio. Knowing that the charge on an electron is ( 1.6021 ± 0.0000)-10-19C, what is the mass of an electron in the electron beam? e) Calculate the mass of an electron including uncertainty.

Answer 1

enex given 2. 2 BE R)

pm 1人

oxle so, Ym R, B RT ? V

x360 20 C 2 요스) 36

Page IST 2.1 a. CC 34 4mニ016634x4.ixto-39 -39 2-7 103