Question 4(ii)
(a) Mention one difference between reflection of light from a plane mirror and total internal reflection of light from a prism
(b) When an empty test tube is placed in a beaker of water and viewed from above, its surface appears as a mirror. Explain.
(a) Difference between reflection of light from a plane mirror and total internal reflection of light from a prism are:
| Plane mirror | Prism |
|---|---|
| In reflection of light from a plane mirror, only a part of the light is reflected while rest is refracted and absorbed. So, the reflection is partial. | In total internal reflection of light from a prism, the entire incident light is reflected back into the denser medium. So there is no loss of light energy. |
(b) Total internal reflection occurs when light traveling through a medium with a higher refractive index (such as water) encounters a boundary with a medium of lower refractive index (such as air) at an angle greater than the critical angle. In this case, the water acts as a more optically dense medium than air.
As a result, the light reflects completely back into the water instead of passing into the air above the test tube. This reflection creates a mirror-like effect on the surface of the water inside the test tube when viewed from above, giving the appearance of a mirror.