Measurement of the refractive index of a liquid by the real and apparent depth method

An object pin, placed at the bottom of a container of water, when viewed from above, appears to be less deep than it actually is. This apparent depth can be measured by finding the position of no parallax between the image of the object pin and the image of a search pin, placed above the container and viewed in a plane mirror which is resting on top of the container. When there is no parallax between the images it means that both images are equidistant from the eye of the observer.

The refractive index (n) of the water is calculated using the formula: n = Real depth / Apparent depth

Procedure:

  1. Using the mouse, drag the search pin to rougly the correct height above the container
  2. Press the "Move Eye" button
  3. The image which is farther away appears to move relative to the other (parallax). Raise or lower the search pin until you find the position of no parallax
  4. Press the "Get Ruler" button
  5. Measure and record the real depth and the apparent depth in a table as shown below
  6. Press the "Container 2" button and repeat steps 1 to 5
  7. Press the "Container 3" button and repeat steps 1 to 5
Real depth (cm)
Apparent depth (cm)
n = Real / Apparent
     

Analysis:

Calculate the refractive index (n) of the water by finding the average value of the three results.

Precautions:

  • Ensure that the water is touching the back of the mirror
  • Avoid parallax errors when reading the real and apparent depths. Get your eye in line with the ruler and object