Confirming Plank's Constant

Purpose:

The purpose of this experiment was to measure planks constant using the spectral lines of different colored LED’s.  The LED’s wave length was measured using the same system as used in the previous experiment.  The Voltage through the LED was measured and graphed with the frequency and the slope of that line was expected to be Plank’s constant.

Method:

Two rulers were set up in an L shape and at the end of one of the rulers was an LED with the gradient at the front of the ruler.  To the right of the LED was another ruler that was used to measure how far the spectral lines appeared to be from the source when looking through the gradient.  A measured Voltage was sent through the LED and the Spectral line were measured to determine the wavelength of the LED.  This was used in determining the frequency.

	D (cm)	L (cm)	Wavelength (nm)	Voltage (V)
Red	191.85	36.3	641.9	1.81
Orange	191.85	33.9	592.4	1.88
Green	191.85	31.8	529	2.48
Blue	191.85	28.4	475.6	2.58

The Energy was determined by multiplying the voltage with the charge of a electron.

	E (J)	1/wavelength
Red	2.90E-19	1.56E+06
Orange	3.01E-19	1.67E+06
Green	3.97E-19	1.89E+06
Blue	4.13E-19	2.10E+06

h=qV/f

Using the relationship above plank's constant which is known to be 6.626E-34 was recorded as:

Red                 6.21E-34
Orange           5.94E-34
Green             7.00E-34
Blue                6.55E-34

Conclusion:

The average experimental value of h came out to be 6.43E-34.  This value when compared to the excepted plank's constant has an error percentage of 3.03% which is an acceptible verification of plank's constant.

Line Spectra Lab

Purpose:

The purpose of this experiment was to measure the wavelength of the spectra of the light emitted from an unknown gas and use the spectra to determine the gas.  A gradient of known attributes was used to see the spectra.

Method:

Two rulers were set up in an L shape and at the end of one of the rulers was a light source with the gradient at the front of the ruler.  To the right of the light source was another ruler that was used to measure how far the spectral lines appeared to be from the source when looking through the gradient.

The target of the experiment was to determine the wavelength of the light emitted from a gas lamp.  To determine this we used a trigonometrically derived equation.

Where d is the spacing between the slits of the diffraction gradient, D is the distance to the spectral lines from the source and L is the distance from the gradient to the source.  

with d being measured as 

d=1.6E-6 m

The first unknown gas was measured with the following data being compiled.

	D (m)	L (m)	Wavelength (measured)nm	Wavelength (actual)nm
Red	0.75	1.57	690	690
Yellow	0.61	1.57	589	580
Green	0.54	1.57	535	545
Violet	0.42	1.57	439	435

Next we measured the Hydrogen spectrum. 

	D (m)	L (m)	Wavelength (measured)	Wavelength (actual)
Red	0.7	1.56	655	656
Blue	0.49	1.56	495	486
Violet	0.43	1.56	447	434

Conclusion:

This method of determining the wave length of light emitted from an excited gas proved to be quite accurate and simple method.  As the excited electrons in the gas raise and lower in shells they release quantized energy that can be calculated through the wavelength of the light.  The data gathered fits well into the uncertainty of the experiment.