# Abstracts of Experiments

# Experiments for PHYS 1146, 1148, 1152, 1156, 1162, 1166, 1172, 1176 and PHY 2302, 2502, 3102 Courses

## 1. Measurement

Students are introduced to basic measurement techniques such as length measurement with a meter stick and vernier caliper, mass measurement with a triple-beam balance and time with a stopwatch. They obtain the volumes of various size cylinders from measurements of the cylinders’ lengths and diameters. After measuring the masses of the cylinders, they calculate the densities of the metals and compare them to the expected values. They also determine the density from all their data by plotting mass vs. volume of the three or four cylinders they measure and finding the slope. Students also measure the time it takes a freely falling ball to hit the ground. Errors, which are relevant to the equipment and measurement methods and their propagation, are determined.

## 2. Free Fall

Students measure the successive positions of a freely falling weight attached to a paper tape onto which a timer makes a mark every 25 msec. From these data, they determine the speed as a function of time, as well as the acceleration (gravity) of the motion. By repeating the experiment with different weights, the independence of the acceleration of a falling object from its mass is investigated. For small masses the paper tape provides a significant drag.

## 3. Motion in One and Two Dimensions

Tracing the path of a puck moving on a frictionless inclined plane, students determine the x and y components of its successive positions at constant time intervals. From these data, puck velocities are obtained. From the velocity data, the accelerations in the vertical and horizontal directions are determined. The independence of the two components of the motion is investigated.

## 4. Newton’s Second Law

Students measure the acceleration of two masses connected to each other by a string that runs over a pulley. One mass moves on a frictionless horizontal table. The other one is freely suspended from the string. Both masses can be varied. Therefore the dependence of the acceleration on force or mass can be studied.

## 5. Uniform Circular Motion

Students measure the average speed of an object in uniform circular motion. They separately measure the centripetal force, which produces this motion. The apparatus consists of a rotating gallows from which a plumb bob is suspended. A horizontal spring attached to the plumb bob provides the centripetal force. Student measure the period of rotation required to stretch the spring a given distance. Then they determine the static force that stretches the spring by an equal length. After repeating this experiment with various springs, they plot angular velocity vs. centripetal force to verify that the centripetal force increases as v^{2}.

## 6. Conservation of Momentum in Collisions

Conservation of momentum is investigated in this experiment. Tracing the path of two pucks that collide with each other on the frictionless air table, students measure the momentum of each puck before and after the collision. By comparing the total momentum and the total kinetic energy of two pucks before and after the collision the conservation laws under the elastic case are investigated. Next inelastic collisions are studied. Attaching Velcro to the pucks makes them stick together in a collision. Momentum and energy conservation under these conditions are studied. Also by tracing the center of mass of the two pucks, the motion of the center of mass of a two-body system is studied.

## 7. Work and Energy on an Air Track

An air track with a computer is used in this experiment. By analyzing the data collected with the computer of the glider on a tilted air track, students measure the glider’s velocities during the motion at fixed time intervals. From this, they get kinetic energy as function of position. They measure the tilt angle which provides the potential energy. From these data they can obtain the gravitational acceleration. Next, velocities of the glider that is moving on frictionless level track under the influence of a hanging mass are measured. By plotting V^{2} against position, the acceleration of the motion is estimated and compared to the theoretical predictions. This experiment is similar to Exp. 10, except here the important quantities used are energies.

## 8. Forces and Torques in Equilibrium

The static equilibrium conditions on a weighted meter stick are investigated. First, by balancing a weighted meter stick on one’s finger, the center of mass is determined. Next, students mount one end of the meter stick on a pivot so that the stick can swing freely in a vertical plane. The other end is then supported by a string attached to a spring scale in different ways such that the meter stick and the support string make different angles with the horizontal. They measure components of forces and of torques acting on the meter stick, calculate the sum of torques and compare to the expected values. Finally, after adding an unknown force to the balanced meter stick, the students estimate the torque caused by this unknown force from the equilibrium condition and compare it to the directly calculated value and verify the equilibrium condition.

## 9. Maxwell’s Wheel

Maxwell’s wheel consists of a vertical aluminum disk mounted on a horizontal axle, suspended on two threads from above. When the disk is rotated, the threads wind themselves on the axle, somewhat similar to a yo-yo, and the disk rises. Once at the top the threads begin to unwind, and the disk falls. Students first measure the dimensions of the wheel plus axle and calculate the moment of inertia. Next they measure falling distances and falling times of the wheel, and determine the downward acceleration. From the motion, they obtain a moment of inertia and compare it to the value calculated in the first part of the experiment. Brass knobs are attached to the Maxwell’s wheel to change the moment of inertia in the last investigation.

## 10. Rolling Motion on an Inclined Track

This experiment is about one dimensional rolling motion of cylinders on U-channel track with adjustable ramp. It introduces the student to the Ultrasonic Measurement System which uses a computer equipped with sonar to collect position and time data of a cylinder moving up and down the track under the influence of gravity. The computer records cylinder’s position vs. time. The students are asked to perform investigations using transparent cylinders, which are filled with water, glycerin and silicone. They collect and analyze trajectories of the cylinders filled with materials of different viscosity, and must explain quantitative differences. The main qualitative analysis step is finding the relation between measured V^{2} and acceleration. As always, the students are asked to compare their results with the theoretical predictions.

## 11. Fluid Flow

After the definition of pressure and Pascal’s Law are explained, students are required to measure the densities of water and glycerin in three different ways. First the densities are determined by measuring the volume and the masses of liquids directly; next by measuring the pressure in a liquid using a manometer, and finally by measuring the buoyancy force of an object in a liquid. By measuring the fluid resistance, the dependence on pressure of the water flow rate through a capillary is studied. The dependence of flow on capillary diameter is also investigated.

## 12. The Simple Pendulum

Students measure the periods of a simple pendulum for several different lengths of string and make a plot of period squared against length. Then they determine the gravitational acceleration from their plot. By repeating the experiment with different mass, they investigate the independence of period on the mass.

## 13. Simple Harmonic Motion

This is an air track experiment. A glider is connected with two springs to the track. When deflected from its equilibrium it oscillates. The motion of the glider is obtained from ultrasonic measurements collected by a computer. The computer can plot position, velocity, and acceleration vs. time. The students find the period of the wave from the position plot. They are next asked to calculate the displacement of the glider at several times and compare their results with the raw data. Next, the students calculate the angular velocity. Using this calculated value, they find the period and compare it to the measured period. Finally, the students are asked to investigate the phase relationships between the position, velocity, and acceleration plots and also show that the period is independent of the amplitude.

## 14. Standing Waves

Standing waves in two different media, a string and an air column, are investigated. In the first experiment, transverse waves are set up in a string, which is fixed at both ends. Near one end is a vibrator that produces the waves. Students measure the wavelength of the standing waves, which are formed when the tension in the string allows the appropriate wave velocity. They calculate the velocity and plot the velocity-squared versus the tension. They verify the relation between the tension and mass per unit length of the string on one hand, and the wavelength of the wave on the other. The students also measure the velocity of sound in air by measuring the wavelength of sound, obtained by listening to a resonance in an air column the length of which can be varied. The sound is produced by a tuning fork held over the air column.

## 15. Geometric Optics

In this experiment students study the law of thin lenses, the difference between real and virtual images and mirror images. In the first experiment, students determine the focal length of a thin lens by measuring the distance between the object and the lens and the distance between the lens and the image. They also examine the magnification law by plotting the ratio of the size of the image to the size of the object against the distance ratio. Then students observe a real image and a virtual image by looking at these two images at the object side of the lens and they compare these two images. Finally, they investigate the mirror images with small cylinders and a plane mirror. By tracing the position of an image, they find the law of specular reflection experimentally.

## 16. Electric Field and Electric Potential

The characteristics of E and V for two different two-dimensional charge configurations are investigated. For parallel Electrodes, students measure the equipotential lines, determine the electric fields and reconstruct the electric field lines near the center of the two electrodes and fringe-fields near the electrode ends. Students repeat the experiment for concentric electrodes and find the radial electric fields for this geometry. The experiment gives a good feel for the relation between E and V, and for graphical representations of E and V.

## 17. DC Circuits

Kirchhoff’s rules are studied for simple series and parallel circuits consisting of batteries or a power supply, circuit element box, some patch cables, and one or two digital multimeters (DMM). The students learn how to use DMMs to measure currents, voltages, and resistances, and the effects of meters on the measurements using basic 2-3 element circuits. Next, the students take and analyze V–I characteristics of simple resistors networks. They compare measured and calculated values of ohmic resistance of the resistors combined in various configurations.

## 18. R–C Circuits

Transient behavior of RC circuits is studied. A circuit consisting of a resistor and capacitor in series is connected to a 6 V power supplies via a switch. As the capacitor is being charged, students measure the change in voltage first across the resistor, then across the capacitor using a DMM and a stopwatch. The RC is large enough so that this works! They determine the time constant in both measurements and compare them to each other and the calculated value. They also explore the exponential behavior of the capacitor voltage by plotting the voltages against the time. As the capacitor is being discharged, the current in the circuit is measured and log of current is plotted as a function of time. The slope of this graph is compared to the time constant found earlier. Finally, the capacitance of two capacitors in series or parallel combination are studied by measuring the new time constant of the circuit.

## 19. Magnetic Force & Lorentz’s Law

First the repulsion and attraction of two ceramic ring magnets are studied, as a qualitative indicator of the strength of magnetic forces. The main experiment is a study of Lorentz’ law *F= ILB* by use of a current balance. The dependence of the magnetic force on a length of wire is measured by balancing it against a known gravitational force. All three variables, *I*, *L*, and *B* can be varied in this experiment, and plots of the magnetic force vs. these three variables verify the linearity of the relation. The experiment also determines the magnetic field strength of the horse shoe magnets used.

## 20. Electromagnetic Induction

Faraday’s Law of induction is the topic of this experiment. First, the voltage produced in a pickup coil by quickly moving a permanent magnet. Then a voltage is produced by quickly moving a pickup coil away from a permanent magnet is found. Next Faraday’s Law is tested in integral form by using a function of the digital oscilloscope. Students are given 2 coils (with an unknown number of turns) and asked to find the number of turns in each coil. In the main part of the experiment, a function generator producing either a sinusoidal or a saw tooth shaped current in a field coil sets up a time varying field. This field induces a voltage in a pickup coil. The field generating current and the voltage of the pickup coil are displayed and measured with a dual trace scope. The dependence of induced emf on the changing magnetic flux is studied.

## 21. Radioactive Decay

The students observe radioactive decay as a random process and measure the half-life of a short -lived isotope. The first investigation calibrates the Geiger tube by collecting data using a computer and plotting on the computer count rate vs. Geiger tube voltage. The students then measure the background radiation using the computer and plot their data using a histogram to find the average background count rate. Next, the students take data from a ^{137}Cs source and histogram it. They observe what percentage of their data lies within one and two standard deviations of the average count rate. Finally, the students investigate effect of shielding on the ^{137}Cs source radiation to determine the absorption coefficient and the half-value layer thickness of lead.

**22. Ideal Gas Law and Absolute Temperature**

By using Ideal Gas Law apparatus with computerized sensors of gas temperature, volume, and pressure, students show that these parameters change according to the Ideal Gas law. Two special cases of the Ideal Gas law are also examined: Gay-Lussac’s and Boyle’s laws. Students are familiarized with absolute temperature scale, the degrees of Kelvin. The value of absolute zero temperature is determined in degrees of Celsius using a constant-volume sphere and digital temperature sensor.

**23. UV-VIS Spectroscopy**

Students are familiarized with physical principles of UV-VIS spectroscopy. They measure hydrogen and helium emission spectrum using analog hand-held and digital spectrometers, and compare results to the on-line spectral database of the National Institute of Standards. The physical origin of discrete line-emission and continuous black-body spectra are explained. Students measure UV-VIS spectrum of a tungsten bulb light source. By comparing to Solar spectrum, they determine the absorption Fraunhofer spectrum. Additionally, students take spectra of fluorescent bulbs, LCD monitors, and hand-held devices they use to compare to the sunlight.

**24. Electrophoresis in Chromatography Paper**

Students familiarize themselves with techniques of chromatography. Motion of a polar molecule under the viscous friction in electrolyte and applied electric field is explained. They measure terminal velocity of food coloring molecules in the chromatography paper strip wetted with baking soda solution. Students run electrophoresis apparatus at 75V and 150V DC to study voltage-dependence of dyes displacement and mobility. Additionally, they investigate no-voltage case to study effects of osmosis, diffusion and gravity.

# Experiments for PHYS 1150 Course

**Ph1. Systematic Errors**

Basic errors in measurements: absolute, relative, percent, systematic and statistical errors, and their propagation in the experimentally measured quantities. Students calculate densities of solid objects, and make estimates of the accuracy.

**Ph2. Statistics and Random Errors**

Students learn how to quantify and improve statistical errors. They use a Geiger counter to measure Earth’s natural radiation background.

**Ph3. Free Fall in 1 & 2 Dimensions**

Velocity, acceleration, potential and kinetic energy, work. Students measure successive positions of a freely falling weight using timer and attached paper tape. They determine the speed as a function of time, and calculate acceleration of free fall due to gravity.

**Ph4. Work and Energy**

Using a computerized air track with ultra-sonic sensor and a glider, students measure velocities, and kinetic energies as functions of position. By calculating potential energy they check energy conservation law and obtain the gravitational acceleration.

**Ph5. Laminar Flow in Capillaries**

Poisseuille’s law of viscous flow is explained. The laminar water flow rate through capillaries is measured as a function of their length, diameter and pressure gradient.

## Ph6. **Viscous Sedimentation**

Motion of a spherical particle under gravity, buoyancy and viscous friction is explained to the students. They measure terminal velocities of stainless steel, nylon and silicon nitride spheres in glycerin and water, and calculate liquid viscosities from the data.

**Ph7. Ideal Gas Laws**

By using computerized sensors of gas temperature, volume, and pressure, students show that these parameters change according to the Ideal Gas law. Two special cases of the Ideal Gas law are also examined: Gay-Lussac’s and Boyle’s laws.

## Ph8. **Absolute Temperature**

The absolute zero temperature is determined using a constant-volume sphere and digital temperature sensor.

## Ph9. Blackbody and UV-VIS Radiation

Students measure black-body spectrum of a tungsten bulb. By comparing to Solar spectrum, they determine the Fraunhofer spectrum. They take spectra of fluorescent bulbs, LCD monitors, and any hand-held devices they use, and compare to the sunlight.

**Ph10. Line Emission Spectra**

Goal is to determine chemical elements by measuring strong spectral lines with grating spectrometer and comparing results to the on-line spectral database of the National Institute of Standards. Students also measure spectral bands in diatomic gases and emission spectra of simple compounds such as CO_{2} and H_{2}O.

**Ph11. Nuclear Decay**

Students start by calibrating a Geiger tube, and measuring background radiation level. Then they take data with individual ^{137}Cs isotope sources, and determine the percent of counts within one and two standard deviations, and outside of three sigmas.

**Ph12. Radiation Shielding**

Students investigate the effect of shielding on the ^{137}Cs source radiation to determine the absorption coefficients and the half-value layer thicknesses of various materials, such as lead, aluminum and plastics.