4(ii)
(a) The refractive index of water is 1.33 at a certain temperature. When the temperature of water is increased by 40°C, the refractive index changes to 'x'. State whether x < 1.33 or x > 1.33.
(b) State two differences between normal reflection and total internal reflection.
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(a) In general, the refractive index of a substance decreases with increasing temperature. Therefore, if the temperature of water is increased by 40°C, the refractive index 'x' is expected to be lesser than 1.33. Hence, we can state that x < 1.33.
(b) Two differences between normal reflection and total internal reflection are:
| S. No. | Normal reflection | Total internal reflection |
|---|---|---|
| 1. | Normal reflection can occur whenever light encounters a reflective surface, such as a mirror, glass, or water, without any specific conditions related to the angle of incidence. | Total internal reflection occurs when light travelling in a denser medium, is incident at the surface of a rarer medium at an angle of incidence greater than the critical angle for the pair of media. |
| 2. | In normal reflection, only a part of the light is reflected while rest is refracted and absorbed. So, the reflection is partial. | In total internal reflection, the entire incident light is reflected back into the denser medium. So there is no loss of light energy. |