Physics - P3 - AQA - GCSE - Refractive Index

Physics - P3 - AQA - GCSE - Refractive Index

1. Refraction - the change in direction when a wave enters a different medium

   • E.G. Air into glass
   • Caused by the change in density in the medium
     • Changes the speed of the wave

2. Speed of waves

   • Decrease
     • Bends towards the normal
   • Increase
     • Bends away from the normal
   • If the wave hits the medium at 90° (along the normal) it does not refract, but the speed will change.

3. The normal is a line at an angle of 90° against the surface of the point of entry on the medium.

4. Refractive index - (when referring to a medium) the ratio of speed of light in a vacuum to speed of light in that medium

   • If an incident ray passes from one medium into another, the angle of refraction of the ray is affected by the refractive index of the material.
   • Refractive index = sin(incident)/sin(refraction)
     • n=sin i/sin r
     • Find out the refractive index of the medium below.
       • n = sin i/sin r
         • n = sin 55/sin 33
           • n = 0.819/0.545
             • n = 1.50
               • Refractive index is 1.5
       • What if we knew the refractive index but not the angle of refraction?
         • n = sin i/sin r
           • 1.5 = sin 55/sin r
             • sin r = sin 55/1.5
               • sin r = 0.5461...
                 • Inverse sin 0.5461... = 33
                   • r = 33°

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