High School and Undergraduate Physics Practicals

With 3D Simulations

Robert Lucas

• Publisher: CRC Press
• Year: 2022
• ISBN:
  9781000572490
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Physics
• Index: Physics

This book describes more than thirty physics practicals at high school and undergraduate levels with background information on each one, a description of the equipment needed, and instructions on how the experiment is performed. Uniquely, for those without access to a real laboratory, the book provides access to highly detailed 3D simulations of all the experiments.

The simulations are a superset of the Virtual Physics Laboratory as reviewed and given the Green Tick of Approval by the Association for Science Education. They run in any browser that supports WebGL, such as Microsoft Edge or Firefox on Windows and Safari on Mac. For the school or university student who wants to practice and widen their knowledge of physics, or for those who are learning on their own, this is an ideal book for honing and broadening experimental skills.

The simulations are the result of many years researching the teaching of online science, a field in which the author has published many papers.

The companion website for the book can be found here: https://www.virtual-science.co.uk/

1 Millikan’s Oil Drop Experiment

DOI: 10.1201/9781003262350-2

Introduction

This experiment is one of the most important ever performed. Joseph John ‘J. J.’ Thomson had identified the electron as a charged particle in 1897 and had measured its charge-to-mass ratio. The next step was to obtain a value for either the mass or the charge.

Robert Millikan was born in Illinois in 1868 and obtained his Physics doctorate in 1895, just two years before Thomson’s experiment. He received the Nobel Prize in 1923 ‘for his work on the elementary charge of electricity and on the photoelectric effect’.

In Millikan’s experiment, he sprayed oil drops into a chamber (C). These drops obtain a charge from the friction of going through the atomizer at (A). These drops fall under gravity through a hole in the plate (M). There is another plate (N) below the first plate, and these are separated by a ring with several windows. One of these windows is used to illuminate the chamber between the two plates, and another window is used to observe the motion of the oil drops.

An electrostatic charge can be applied to the plates. This charge can be varied, and it allowed Millikan to balance the force due to gravity against the electrostatic force and bring the particles to a standstill. It is this balancing of forces that allowed Millikan to determine the charge on an electron. One small detail remains, and that is that the oil drops had a number of charges on them that only sometimes would be due to a single electron. So Millikan observed the motion of particles with multiples of the electron charge. This meant that he had to do many observations and look for the ones that had the least charge on to find the single charge amount.

In our version of the experiment, tiny (1.02 microns across) polymer balls are used instead of oil. We use an equation of motion that balances the forces due to gravity, drag, and the electrostatic. As with Millikan’s version, we get a distribution of the number of charged electrons on our polystyrene balls.

• Question: What is the volume of a single polymer ball?
• Question: What is the mass of a single polymer ball given that the density is 1.05 g/ml?

FIGURE 1.1 Millikan’s drawing of his apparatus.

The Objective

To find the charge on a single electron.

The Apparatus

The apparatus is shown in Figure 1.2.

FIGURE 1.2 View of the experiment’s simulation.

You will need:

• A high-voltage power supply for the plates with polarity and voltage control
• A low-voltage power supply for the light bulb
• An electrostatic chamber
• A multimeter
• A bottle of polymer balls
• A squeeze atomizer
• A light source
• A telescope or webcam with reticle
• A micrometer

The kit can either be sourced in the form shown in Figure 1.2 or assembled from the components listed. The electrostatic chamber is the small box behind the webcam and to the left of the light. In this case, it was supplied as part of the main unit, but it can be sourced as a separate item. It consists of two metal plates held apart by a transparent separation ring. The metal plates are fitted with connectors so that they can be connected to a high-voltage electrical supply. There are three other holes into the internal chamber: one for introducing the particles, one for letting light in so that the particles are illuminated, and one for observing the interior of the chamber.

FIGURE 1.3 Schematic of the electrical circuits.

The space between the plates is viewed using a webcam, although it can also be viewed directly by eye through a telescope. This is considerably less convenient due to how easy it is to disturb the equipment. The image is displayed on the screen when the chamber is illuminated, and the webcam is activated. The high- and low-voltage supply is the box behind the chamber. To the right of the chamber, you can see the light source. The low-voltage output is connected to the light. The high-voltage output goes to the box that controls the polarity and voltage. A meter to the left of the power supply indicates the voltage difference between the plates. There are controls on the unit below the chamber for varying the voltage and reversing its polarity.

The atomizer is to the left of the electrostatic chamber and is filled with a solution containing the polymer balls. Squeezing the bulb of the atomizer sends a puff of balls into the chamber.

The Variables

The independent variable is the voltage, and we are going to measure the speed of the polymer particles, which is the dependent variable.

The Physics

When the polymer particles are moving inside the chamber, they can be considered to be at their terminal velocity. Although for some of the time they are accelerating because they are so light, they reach their terminal velocity almost immediately. Therefore, in all cases we can consider that the forces acting on the particles cancel out; that is, upward forces equal downward forces. We are going to observe the velocities of the polymer balls as they move upwards. In this case:

FIGURE 1.4 The forces acting on a polymer sphere.

V_t is the terminal velocity, which in this case (and the cases we are going to observe) is an upward drift. The upward force on the particle is F_e, the electrostatic force. The downward forces are F_g, the force due to gravity, and F_d, the force due to viscous drag. The forces balance, so we can write:

F_e = F_g + F_d

The electrostatic force is given by:

F_e = qE

Where E is the field, which in this case is simply described as the voltage divided by the distance between th...

Table of contents

• Cover
• Half Title
• Title
• Copyright
• Dedication
• Contents
• About the Author
• Introduction
• 1 Millikan’s Oil Drop Experiment
• 2 Planck’s Constant
• 3 Rutherford’s Gold Foil Experiment
• 4 Measuring the Acceleration Due to Gravity
• 5 Average Velocity Using an AirTrack
• 6 Determining Acceleration Using an AirTrack
• 7 Confirmation of Newton’s Second Law
• 8 Showing Conservation of Energy Using an AirTrack
• 9 Conservation of Momentum in an Inelastic Collision Using an AirTrack
• 10 Hooke’s Law
• 11 Young’s Modulus
• 12 Velocity of Rifle Shell Using a Ballistic Balance
• 13 Simple Pendulum
• 14 Simple Harmonic Motion Using a Mass-Spring System
• 15 Capacitor Charge and Discharge
• 16 The Internal Resistance of a Dry Cell
• 17 The IV Characteristics of a Diode
• 18 The IV Characteristics of a Filament Lightbulb
• 19 The Resistivity of Constantan
• 20 Resistors in Series and Parallel
• 21 Heat Transfer
• 22 Boyle’s Law
• 23 Charles’s Law
• 24 Mechanical Equivalent of Heat
• 25 Specific Heat Capacity of Brass
• 26 Investigation of Mechanical Waves
• 27 Measuring the Speed of Water Ripples
• 28 Infrared Radiation
• 29 Diffraction Using a Monochromatic Laser
• 30 Inverse Square Law for Gamma Radiation
• 31 Refraction of Light
• 32 Magnetic Field Due to a Coil of Wire
• 33 Investigation of Magnetic Flux of a Current-Carrying Wire
• 34 Magnetic Flux Linkage
• Appendix 1 Uncertainties
• Appendix 2 Using Excel for the Results
• Appendix 3 Controlling the Simulations
• Index