PASCO Specialty & Mfg. SP-9268A User Manual download pdf (Page 11)

012-02135F Student Spectrometer

To Measure the Angle of Minimum

Deviation:

Align and focus the spectrometer as described earlier.

2. Use the two thumbscrews to attach the prism clamp

to the spectrometer table and clamp the prism in

place as shown in Figure 10.

3. Place the light source a few centimeters behind the

slit of the collimator. (It may be helpful to partially

darken the room, but when using the prism this is of-

ten not necessary.)

4. With the prism, it is generally possible to see the re-

fracted light with the naked eye. Locate the general

direction to which the light is refracted, then align the

telescope and spectrometer table base so the slit im-

age can be viewed through the telescope.

5. While looking through the telescope, rotate the spec-

trometer table slightly back and forth. Notice that the

angle of refraction for the spectral line under observa-

tion changes. Rotate the spectrometer table until this

angle is a minimum, then rotate the telescope to align

the vertical cross-hair with the fixed edge of the slit

image. Use the fine adjust knobs to make these ad-

justments as precisely as possible, then measure the

telescope angle using the vernier scale.

6. Without changing the rotation of the spectrometer

table, remove the prism and rotate the telescope to

align the cross-hair with the fixed edge of the

undiffracted beam. Measure the angle on the vernier

scale. The difference between this angle and that re-

corded for the diffracted spectral line in step 5, is the

angle of minimum deviation. Notice that, since the

determination of the angle of minimum deviation for

each spectral line requires rotational adjustments of

the spectrometer table, the angle of the undeflected

beam must be remeasured for each line.

LIGHT

SOURCE

PRISM CLAMP

PRISM

Figure 10 Mounting the Prism

1 2 ... 6 7 8 9 10 11 12 13 14 15 16

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PASCO Specialty & Mfg. SP-9268A User Manual Page 11