The diagram shows light incident on the centre of a semi circular glass block - Edexcel - GCSE Physics - Question 6 - 2016 - Paper 1

Since angle Y is greater than the critical angle, the ray of light will reflect internally at point P. You must indicate the angle of incidence greater than the critical angle leading to total internal reflection.

As light travels from air (less dense medium) into glass (denser medium), it slows down, resulting in refraction. The change in speed causes the light to bend towards the normal. This bending or change of direction occurs due to Snell's law, described by the formula: $n_1 imes ext{sin}( heta_1) = n_2 imes ext{sin}( heta_2)$ where n_1 and n_2 are the refractive indices of air and glass respectively.

The formula for power (P) of a lens is given as: P = rac{1}{f} where f is the focal length in meters. Given that the focal length f is 0.25 m:

Substituting the values: P = rac{1}{0.25} = 4.0 Thus, the power of the lens is 4.0 diopters.

In the fibre optic lamp, light is being transmitted through optical fibers, showcasing total internal reflection, allowing the light to travel long distances without significant loss.

In the plane mirror, the light reflects off the mirror's surface, following the law of reflection where the angle of incidence equals the angle of reflection. This allows for clear images to be formed, as no light passes through the reflective surface.