6.7   Refractive index

6.7.1   Immersion method

6.7.1.1  Take a few glass beads and put them on the grooved glass slide and immerse them in a liquid with a known refractive index

6.7.1.2  Place the grooved film on the microscope stage, adjust the condenser to the maximum setting, adjust the microscope aperture to the maximum, and turn on the microscope light source

6.7.1.3  Move the blackboard with a straight edge of about 10cm×10cm to the condenser, through the eyepieces you can observe that half of the visible area is dark and the other half is bright

6.7.1.4  Observe with reference to Figure 2 to determine the refractive index of the glass beads and the refractive index of the liquid.

6.7.1.5  Repeat the above steps with liquids with different refractive indexes until a liquid with the same refractive index as the glass bead is found, or two liquids with similar refractive indices are found, and the refractive index of the glass bead is between the refractive indices of the two liquids.The refractive index of the liquid can be measured with an Abbe refractometer and corrected to 20°C.The refractive index of common liquids at 20°C is shown in Table 2.

The refractive index of glass beads is greater than that of liquid

Shadow on the blackboard

The refractive index of glass beads is equal to the refractive index of the liquid

Shadowless, with colored edges

The refractive index of glass beads is less than that of liquid

Shadow on the opposite side of the blackboard

Figure 2 Determination of the refractive index of glass beads

GB/T 24722-2020

Table 2

Common liquid refractive index at 20 degrees

Note: Refraction fluid can be purchased on your own or you can find someone to configure it

Test judgment method

Units with conditions can purchase a microscope connected to a computer digital display, so that the test results can be observed more clearly, as shown in the figure below:

Correct test result: