Experiment: Planck’s constant form an LED

The purpose of this experiment is to experimentally determine Plack’s constant by an LED.

The equation used was qV=hc/λ. Solving for Planck’s constant, we get:  h = qVλ/c

Procedure:

We built the setup above to measure the voltage of the LED of various colors when it is dimmest.  In order to make the LED dim, we used varying amount of resistances.  To determine wavelength used a previous method in the color and spectra experiment.

Data:

LED	Voltage(V)	D(cm)	L(cm)	λ(nm)	h (Js)	% error
Red	1.43	28.5±1	86±1	629	4.80±0.20x10^ -34	27.6
Yellow	1.59	26.5±1	86±1	589	4.99±0.23x10^ -34	24.7
Green	1.92	23.5±1	86±1	527	5.40±0.27x10^ -34	18.6
Blue	2.00	22±1	86±1	496	5.27±0.31x10^ -34	20.3

Analysis:

The closest to the actual value of Planck’s constant of 6.62x10^-34 was the green LED with 5.40±0.27x10^ -34.  This large error was due to the low voltage read on the meter because of our set up.

ActivPhysics: 18.3

ActivPhysics: 18.3

The Laser

Q1:  Yes, N­­_in­ = N_out+N_cavity­­+n_exieted­:  9 = 2+2+5

Q2:  Random

Q3:  Random

Q4:  Emission is in the Same direction and doubled.

Q5:  Population inversion in pumping level of 80.

Q6: Spontaneous

Experiment: Color and Spectra

The purpose of this experiment was to experimentally measure the wavelength of the colors of light, hydrogen, and an unknown gas.

Procedure:

We used the setup below to find the distance of specific color bands through a diffraction gradient.

The equation used to find the wavelength was:

L is the length, which is 1.90m. D is the distance of the color band.  d is the slit spacing of the diffraction gradient, which is 1/500mm.

Data:

Light

	D(cm)	λ(nm)
Shortest	40	412
Longest	77	751
Blue	49	499
Green	54	547
Yellow	58	584
Red	68	674

Using the shortest and longest wavelength, and the fact that average humans can see between 390nm to 750nm, we found an equation to help reduce the systematic error.

We plug in the calculated values of λ, and get a new wavelength that is more accurate. I will call this λ’.  

Hydrogen

The actual value for hydrogen was calculated by:

	D(cm)	λ(nm)	λ'(nm)	actual values of λ(nm)	% error
End of violet	42	432	411	410	0.002
Middle of cyan	48	490	473	434	0.09
Red	67	665	658	656	0.003

Unknown Gas

	D(cm)	λ(nm)	λ'(nm)
1st violet	43	441	421
Last red	74	726	723
Cyan	47	480	462
Green	53	537	523
1st yellow	59	593	582
Orange	61	611	602
Brightest red	65	647	640

Analysis:

The unknown gas was determined to be Neon because of its very distinctive pattern with many color bands.

ActivPhysics: 17.1 and 17.2

Q1:  The distance of the moving light clock is longer. If we assume the angle is 45­­^0­­ then

distance is 1.414 times longer

Q2:  The time of the stationary light clock is 6.67s and the moving lock is 9.40s

Q3:  No, in your frame of reference the light clock does not travel a longer distance when

moving

Q4:  When velocity of the light clock decreases the time difference decreases.

Q5:  8.004s

Q6: Lorenz Factor = 1.1169~1.12

Relativity of Length

Q1:  The time measurement of the round trip does not matter.

Q2:  If measure form earth, it will be longer.

Q3:  As time decreases, the length needs to be smaller.

Q4:  L = 769.12

Experiment 12: CD Diffraction

The purpose of this lab was to calculate the grove spacing on a CD and DVD.

Procedure:

We shine a laser through a hole in a piece of cardboard to a CD or DVD.  We then measure the reflected interference maxima at a certain distance.

Data:

The equation used was sinθ = mλ/a. Then sine is replaced for values of length and slit distance, and solve the equation for a, the grove spacing.  We get:

λ is the lasers wavelength, and m is the order.

	λ(nm)	m	y(cm)	L(cm)	a(nm)
CD	632	1	4±0.1	10	1702±51
DVD	632	1	15.1±0.1	10	752±61

Analysis:

The manufacturer’s standard value is 1600 nm for a CD.  We got 1702±51nm which does not exactly fall into our error range, but it is close.  The DVD has a much smaller slit spacing, which we calculated it to be 752±61nm.

Experiment 11: Measuring a human hair

The purpose of this lab was to accurately measure a human hair using the concepts of the interference of light though a slit.  To compare, we also used a micrometer to measure thickness as well.

Procedure: we taped a hair though a hole in an index card.  Then we passed a laser though it and measured the distance between the maxima and minima of the pattern produced.

Micrometer

The equation:

λ = dy/Lm

Solving for the diameter of hair d, we get d = λLm/y. 

The wavelength is given at 632nm. L is the distance to the projection, which was 1m.  Y is the distance between the maxima and minima.

Data

	λ(nm)	m	y(cm)	L(m)	d(mm)	micrometer(mm)
Tim	632	5.5	0.58±0.5	1	0.60±0.057	0.05±0.005
Erwin	632	3	2.44±0.5	1	0.078±.002	0.06±0.005

Analysis

When we did Tim’s hair we used the small slit spacing to calculate m.  This gave us an order of magnitude of error.  We calculated 0.60±0.057mm, when the micrometer measured 0.05±0.005mm.  When we used my hair we used the large spacing.  The hair had a calculated diameter of 0.078±.002mm.  The micrometer measured 0.06±0.005mm.  My hair had a much closer value, even though it does not fall within our margin of error. For comparison, the average diameter for black hair the professor provided was 0.05mm.   

The large slit spacing was the actual interference pattern that needed to be used.  The small slits were probably some internal interference.

Final Project Proposal

Cloud Chamber

members

Erwin Peralta
Tim Elsen

We will make a cloud chamber with 99% isopropanol and felt a light source and sheet of metal and plastic container.  We intend to show cosmic radiation interaction with isopropanol to create visible trails.  The cosmic radiation will ionize the alcohol and condense them.  We study elements of magnetic deflections in a magnetic filed by introducing a magnet.  Americium from a smoke detector will be used to show particles as well.  

Criteria for success

• Visibly see ionization trails cosmic or from Americium.
• See the influence by adding a magnetic field 

Initial Design

Gantt Chart