Waves & optics

The human eye is sensitive to electromagnetic radiation in the range of approximately 400 nm to 700 nm, spanning from violet to red light. Option A is incorrect because 100 to 400 nm corresponds to the ultraviolet region, which is invisible to humans. Similarly, option C represents the infrared spectrum.

Total internal reflection requires light to travel from an optically denser medium to a rarer medium at an angle of incidence greater than the critical angle. Option A is incorrect because light moving from a rarer to a denser medium bends toward the normal, meaning it can never reflect back entirely.

The speed of light in a medium is calculated by dividing the speed of light in a vacuum (3 x 10^8 m/s) by the refractive index of 1.5, which equals 2 x 10^8 m/s. A diagram for this topic isn't available yet — the worked example below walks the same reasoning step by step.

• !Option B is incorrect because it represents the speed of light in a vacuum, ignoring the slowing effect of the medium.
• !Option A is incorrect because 100 to 400 nm corresponds to the ultraviolet region, which is invisible to humans.
• !Option A is incorrect because light moving from a rarer to a denser medium bends toward the normal, meaning it can never reflect back entirely.

Answer each from memory — you'll see instantly whether you're right and why.

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