PHGN-398A Fall

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Instructors: Vince Kuo, Patrick Kohl and Frank Kowalski

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Creativity in Science and Engineering

PROBLEM 1: Measuring the wavelength of an unknown laser: What apparatus would you use to measure the wavelength of an unknown laser using a He-Ne laser whose wavelength is know to 8 significant figures?

Green Hat comments

Apparatus:

-two slit interferometer -Superimpose the two laser beams with a beam splitter. Look at the time dependent detector output for beats and take a Fourier transform.

-Superimpose the two laser beams with a beam splitter then shine them on a grating. Look at the spatial separation.

-Superimpose the two laser beams in a Michelson interferometer. Then measure constructive interference of each color and compare.

-Superimpose the two beams and shine them into a parallel plate device (Fabrey-Perot) interferometer. Vary the plate spacing and compare the maxims observed.

-Shine the two beams in a "funnel" absorbing chamber and look for where each is extinguished.

-Cross the two beams at a known angle and look for the spacing of the fringes.

-Measure the combined color of the two beams together.

-Measure standing waves in a cavity whose size is changed.

-Use a dielectric material with a known index of refraction to measure cause a know phase shift and measure its effects.

-Look at the diffraction pattern as both beams traverse a single slit interferometer.

-Beat Frequency

-Diffraction Patterns

idea taxonomy comments

idea of using diffraction. Fluency involves single slit, double slit, grating . . .

idea of using an interferometer. Fluency involves a Michelson interferometer, Fabry-Perot interferometer, . . .

idea of measuring the beat frequency. Fluency involves combining the waves in a detector and measuring the beat, . . .

White Hat comments

Descriptions of grating spectrometer are found at these two links:

[1]

[2]

The resolution of a grating spectrometer, or the smallest change in wavelength measurable divided by the wavelength is the order number times the number of grooves illuminated, which is about 1 part in 2 for a double slit "grating" and about 1 part in 10,000 for an expensive spectrometer. This is discussed in the following link:

[3]

A Michelson or Fabry-Perot interferometer has a change of a fringe every time one mirror is moved half a wavelength. For a mirror motion of 1 meter the number of fringes for the He-Ne laser (wavelength of 6328 Angstroms) is 1.58 million fringes. How many fringes for the unknown laser if both beams were superimposed? How does this resolution compare with the grating spectrometer?

Problem 2: Measuring the Mass Extracted from a Quarry

Green Hat comments

-measure the weight of the trucks carrying the material out of the quarry.

-measure the effect of mass loss on the gravitational attraction.

-measure the volume extracted and determine the mass from its density.

-measure the flow rate of material on a conveyor belt.

-use fuel consumption in the trucks to measure energy required to move the mass.

-measure the mass as it is loaded on the truck via a scale on the scooper truck.

-use Archimedes principle to measure displacement and therefore volume. Density gives mass.

idea taxonomy comments

idea of using a scale to weigh the rock. Fluency involves weighing a truck, the machine which picks up the rock, . . .

idea of fuel consumption in moving the rock. Fluency involves measuring the gas used by a truck over a know trajectory, . . .

idea of measuring the volume remove. Fluency involves using a laser ranging system to map the quarry before and after . . .

idea of measuring the flow rate. Fluency involves using a conveyor belt, some slide that the rock moves down, . . .

combining ideas comments

Fluency: I think there are basically 3 ideas, and not much originality

-Weighing with scale.

-Volume displacement with mass density.

-Flow rate.

Problem 3: How could you convert wind energy into a useful form using a non-turbine (non-propeller) device?

Green Hat comments

-large balloon to convert elastic energy into useful energy.

-cones to funnel the wind into a region where it moves faster.

-use ribbons which jiggle in the wind to capture the wind energy.

-kite to capture wind energy.

-wind pushes cart attached to piston.

-sail moves wire through a magnetic field to generate electricity.

-wind pushes magnets through a coil to generate electricity.

-use cool air and warm earth to get a temperature differential for the thermoelectric effect.

-use a "water wheel" device but with wind rather than water moving it.

-use wind chill factor wind has for a temperature differential and the thermoelectric effect.

-wind rug (needs more explanation).

-streamers attached to a device which converts their motion to electricity.

-wind through a funnel and onto a "water wheel" type of device.

-convert the energy of whipping flags.

-concentrate the wind in a pipe and use it to stoke a fire.

-use the drag force of the wind on a stationary object to generate heat and convert the heat to electricity.

-use the wind to trigger potential energy in a system (rock slide).