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Total Internal Reflection: When Glass Becomes a Perfect Mirror
Light normally leaks out when it meets a boundary: some reflects, some refracts. Under one precise condition, none leaks and every bit is reflected. That is total internal reflection (TIR), and it explains the sparkle of a diamond, the glitter of an air bubble in water, the periscope, and the optical fibre that carries the internet under the oceans.
The topic splits into two linked halves. First, the physics of TIR: its two conditions and the critical angle formula. Second, the optical instruments built on lenses and mirrors: simple microscope, compound microscope, telescope and camera. Exams ask the first half as reasoning ("why does a diamond sparkle?") and the second half as formulas ("find the magnification").
Master one relation, sin C = 1/n, and one habit, matching each instrument to its lens type and focal-length pattern, and this whole chapter turns into quick marks.
1. Total internal reflection occurs when light travels:
2. The refractive index of a medium with respect to air is √2. What is its critical angle?
3. In an optical fibre, the core has ______ refractive index than the cladding.
4. A cut diamond sparkles brilliantly mainly because:
5. A simple microscope consists of:
6. A simple microscope has a lens of focal length 5 cm. Its magnifying power when the image forms at the near point (D = 25 cm) is:
7. An astronomical telescope has an objective of focal length 100 cm and an eyepiece of focal length 5 cm. In normal adjustment, its tube length and magnifying power are:
8. Large astronomical telescopes use a concave mirror instead of a lens as the objective mainly because the mirror: