PHY13L - E406 - PHOTOMETRY

DATA and OBSERVATION

 

TABLE 1. Inverse Square Law
	Transmittance	Experimental r2		%Error
r1 = 30cm	100% (I2 =  I1)	29 cm	30 cm	3.33%
	75% (0.75I2 =  I1)	25 cm	25.98 cm	3.77%
	50% (0.50I2 =  I1)	20.9 cm	21.21 cm	1.46%
	25% (0.25I2 =  I1)	14.7 cm	15 cm	2.00%
r1 = 45cm	100% (I2 =  I1)	44 cm	45 cm	2.22%
	75% (0.75I2 =  I1)	37 cm	38.97 cm	5.06%
	50% (0.50I2 =  I1)	31 cm	31.82 cm	2.58%
	25% (0.25I2 =  I1)	22 cm	22.5 cm	2.22%

 

 

TABLE 2. Polarization

 

Transmittance	Observation at 0°	Observation at 90°	Observation as polarizers are  rotated
100%	Not the same	dark	When 180°, it is same as the observation at 0°
	Experimental Φ		%Error
75% ()	30°	30°	0%
50% ()	45°	45°	0%
25% (0.25I2 =  I1)	50°	50°	0%

 

 

GUIDE QUESTIONS

How does varying the locations of the light sources with respect to the photometer affect the result of the experiment?

The intensity of the light as seen on the photometer depends on the distance of the light source. As the distance between the light source and the photometer decreases, the intensity of light increases and the other way around. 

How are the neutral density filter and polarizer different? In what way/s are they the same?

A neutral density filter or ND filter is a filter that reduces and/or modifies intensity of all wavelengths or colors of light equally, giving no changes in hue of color rendition. It can be a colorless (clear) or grey filter. A polarizer is an optical filter that passes light of a specific polarization and blocks waves of other polarizations. It can convert a beam of light of undefined or mixed polarization into a beam with well-defined polarization.

If you have two pairs of sunglasses, how would you test whether the sunglasses use polarized lenses or not without using polarizers?

Place the two pairs of sunglasses next to each other and rotate on of the pair of sunglasses. If the visibility of the light on the other side is changing, the sunglasses are polarized but if it's just the same, the sunglasses are not polarized.

 

SAMPLE COMPUTATION

TABLE 1

r_2act "=" √((I_1 〖r_1〗^2)/I_2 ) "=" √(〖r_1〗^2 )=30cm

"% Error=" |"30-29" /"30" |"×100=3.33%" 

TABLE 2

θ_act "="  cos^(-1)⁡√(I_1/I_2 ) "="  cos^(-1)⁡√(〖0.75I〗_2/I_2 )=30°

"% Error=" |"30-30" /"30" |"×100=0%" 

 

ANALYSIS

At 100% transmittance, are the distances of two sources from the photometer equal? Is it the expected result? Explain.

The distances, as expected, are equal. Since at 100% transmittance allows all of the light to pass through it and gives the same amount of light as.

At transmittance below 100%, how do the distances of the sources from the photometer compare?

The lower the percentage of the transmittance the closer the distance of the light source from the photometer and the other way around.

If the neutral density filter is set up to a transmittance below 100%, how should the orientation of the polarizers be change to produce the same illumination on both sides of the photometer?

If lower transmittance is used, we need to arrange the polarizer closer to zero degrees of for higher transmittance; it is moved closer to 90o.

CONCLUSION

Based on the experiment, it is found out that photometry can be used to determine various factors affecting the intensity of light and how can it be manipulated through a photometer. It is also concluded that the intensity of the light (luminosity) observed from a given view varies with respect to its distance from the light source. For shorter distances, light is more luminous.

Finally, light is multicomponent, and is polarized in all directions. When it is allowed to pass through a polarizer, it will be linearly polarized, having only one direction. When a second polarizer is used, the light that can be transmitted varies on the angle between the two polarizers. For angle is equal to 0o, the same amount of light from the first polarizer can passed through. On the other hand, as it approaches 90o, the intensity decreases for only component of the linearly polarized light is allowed to pass. At 90o, no light can be observed.