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PHY124 Lab 7 - Reflection, Refraction and Images

There are two parts to this lab which can be done in either order In Part I you will study the Laws of Reflection and Refraction, measure the index of refraction of glass and observe dispersion. In Part II you investigate images produced by lenses.

Part I


  • “Ray” table
  • Triangular prism


The laws of reflection and refraction


When the light beam hits the air–glass boundary, side 1 of the prism in Fig. 2 above, reflection and refraction occurs (see Ch21 sheet 8,9). A small fraction of the intensity of the incident beam is reflected, leaving a faint reflected ray outside the prism, and the remainder of the intensity is refracted into the prism. The refracted ray hits the glass-air boundary on side 3 of the prism and the ray is again refracted into the air as the “exit” ray in Fig. 2 above. The ray reflected inside the prism on boundary 3 is barely visible.

The law of reflection states that the incident angle equals the angle of reflection (Ch21 sheet 8)


For refraction, Snell’s Law holds. Snell’s Law is given on Ch21 sheet 9;


In our case for boundary 1 is the index of refraction of air (which we assume to be 1 as for vacuum) and is the index of refraction of glass. In this lab is considered to be unknown and you will be measuring it by applying Snell’s Law on boundaries 1 and 3.


Make sure the lamp is as close as possible to the slits. Using a piece of paper, block all beams except the central beam, then place a sheet of paper onto the trace table (secure it with the clamps on each corner). Position the triangular prism so that side 1 is ~45o with respect to the incident ray direction as shown in Fig. 2 above. Trace the incident, reflected and exit rays (shown in Fig. 2) and trace the outline of the prism.

Closely inspect the exit ray. You should notice that it has a blue side and a red side. On your sketch, record which side of the exit ray shows which color. You will use this information during Section 3 of Part I, which deals with dispersion.

Make sure your paper stays fixed in place while you are tracing.

phy124/lab_7.1269918579.txt · Last modified: 2010/03/29 23:09 by mdawber
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