Measurement of the Diffraction Grating Spacing (d) using Sodium Light 1. Turn on

Question

Measurement of the Diffraction Grating Spacing (d) using Sodium Light 1. Turn on the sodium lamp; it takes a while to reach full luminosity, so continue with the procedures below. 2. Rotate the degree plate by holding onto the knob (or screw) under the light sensor arm until the face of the grating plate is perpendicular to the light sensor. The grating surface should now be parallel to the zero degree line on the degree plate it sits on. 3. Record your gain setting here. If you start with a gain setting of 10, and then need to switch to gain 100 when the signal is low, how must you scale your low signal intensity values so that all measurements are consistent? 4. Place the sodium lamp in front of the collimating slits, ensuring that the main beam is not passing through the slit at an angle and that the center of the beam is directly over the slit. 5. Once the lamp has reached full luminosity, you should see the m = 0 ("zeroth order") line on the white aperture holder in front of the light sensor. Get the line to appear as sharp as possible. Do this by experimenting with the position (s) of the collimating lens and/or focusing lens. The collimating lens should generally be about 10 cm from the collimating slit. 6. If you want to view a graph of the diffraction spectrum from your lamp passed through the grating in Capstone^TM, what two quantities should you

Explanation / Answer

Gain and offset dictate the signal intensity and noise level of an image, they are the key settings on a microscope:

• the gain adjusts the signal amplification at the detector sensor: or it amplifies the signal and the noise; the lower the gain, the better the signal-to noise ratio or longer exposure times on a cooled camera have less effect on the noise level.xz

• the offset is the minimal signal intensity detected by the sensor, the higher the offset, the more background (and signal) is cut off Gain / Offset (and exposure time) must be set in a way that none of the signal is lost, but the whole available range of brightness levels (dynamic range) is used for imaging.

You are asked to adjust this offset from 10 to 100,so you are reducing the background and increasing the intensity of the sodium light.

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