PASCO OS-8520 PHOTOMETER - Manual (Page 5)

5
012-05631A Photometer
The component, E, of the polarized electric field, E
o
, is found by using trigonometry: E = E
o
cos
φ
.
Since the intensity of the light goes as the square of the electric field, the transmitted light inten-
sity is given by I = I
o
cos 2
φ
, where I
o
is the incident light intensity and
φ
is the angle between the
axis of polarization of the incident light and the polarizer.
Notice that the two extremes work in this formula:
➀ If
φ
is zero, cos 2 (
φ
) equals one, and thus the intensity transmitted is equal to the incident inten-
sity of the polarized light because the polarizer is aligned with the incident light and will allow
all of it to pass through.
➤ NOTE: It is assumed that the incident light is polarized, not unpolarized.
➁ If
φ
is 90
°
, cos 2 (
φ
) equals zero, and no light is transmitted since the polarizer is oriented perpen-
dicular to the plane of polarization of the incident light.
Set Up
➀ Place the photometer in the middle of the optics
bench. Place the neutral density filter on one
side of the photometer. See Figure 2.3.
➁
Place a point light source on each end of the
optics bench.
➂
Snap one polarizer onto each side of the acces-
sory holder. Before beginning the experiment,
check the angle calibration on the polarizers in
the following way: On the side of the acces-
sory holder that has the label, set the angle to
90 degrees. Look through both polarizers at a
bright light and rotate the other polarizer until
the transmitted light is at the minimum. Now
the polarizers are crossed at 90 degrees. Rotate
the label- side polarizer back to zero degrees.
Now the two polarizers are aligned for maxi-
mum transmission. Throughout the experi-
ment, only rotate the label-side polarizer.
➃ Place the polarizer accessory holder (with polarizers) on the bench between the light source and
the photometer on the side opposite the neutral density filter. The label side of the polarizer
holder should face away from the photometer. The polarizer holder should be close to the pho-
tometer so only polarized light will enter that side of the photometer.
Figure 2.3: Experiment Set-Up
Point Source
Point Source
Polarizer
Indicator
Polarizer
The bench and light source shown with the
Photometer are available as part of the
PASCO OS-8515, Basic Optics System