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Revise: Applications of Light and Optical Instruments

How the camera, the eye, microscopes, telescopes, lasers, fibre optics, spectrometers and photometry all put light to work.

The Camera

1/f = 1/v + 1/u — forms a real, inverted image.

f=0.05m, u=3m → v≈0.0508m.

The Human Eye

P = 1/f. Myopia: negative P. Hyperopia: positive P.

Far point 2m → P=−0.5D.

The Compound Microscope

M ≈ (L/f₀)(D/fₑ) — two magnifications multiply.

L=0.18,f₀=0.005,fₑ=0.025 → M=360.

The Telescope

M = f₀/fₑ.

f₀=1.0m,fₑ=0.02m → M=50.

The Laser

E = hf = hc/λ. Coherent, monochromatic, directional.

λ=632.8nm (He-Ne) → E≈3.14×10⁻¹⁹J.

Fibre Optics

θc = sin⁻¹(1/n) — total internal reflection beyond θc.

n=1.5 → θc≈41.8°.

The Spectrometer

d sinθ = mλ.

500 lines/mm, λ=600nm → θ≈17.5°.

Photometry

E = I/d² — inverse-square law.

I=100cd, d=2m → E=25 lux.