WAEC Physics 2019 Paper

Concept:Total internal reflection occurs only when light travels from a denser medium to a rarer medium.That is, the refractive index of the incident medium must be higher than the refractive index of the second medium.Explanation:For total internal reflection, the condition is $n_1 > n_2$, where $n_1$ is the refractive index of the incident medium and $n_2$ is the refractive index of the refracting medium.In option C, light travels from air to water.Here, $n_{\text{air}} < n_{\text{water}}$, so light is going from a rarer medium to a denser medium.This does not satisfy the required condition for total internal reflection.In options A, B, and D, light travels from a denser to a rarer medium, such as $n_{\text{glass}} > n_{\text{water}}$, $n_{\text{kerosene}} > n_{\text{air}}$, and $n_{\text{water}} > n_{\text{ice}}$.Therefore, total internal reflection is possible in those cases but not in air to water.Answer:C. air to water