NSAA Physics - Waves and Optics Flashcards

A convex lens of focal length 20 cm forms a real image of an object 60 cm away. How far from the lens is the image?

Answer: 30 cm

1/f = 1/v - 1/u (real is positive): 1/20 = 1/v + 1/60 → 1/v = 3/60 - 1/60 = 2/60, v = 30 cm.

What is the intensity relationship between two points at distances r₁ and r₂ from a point source?

Answer: I₁/I₂ = (r₂/r₁)²

Intensity from a point source follows the inverse square law: I ∝ 1/r², so I₁/I₂ = (r₂/r₁)².

When light travels from a medium with refractive index 1.5 into air (n=1), what is the critical angle?

Answer: 41.8°

sin(θc) = n₂/n₁ = 1/1.5 = 0.667, so θc = arcsin(0.667) ≈ 41.8°.

Which wave property allows sound to be heard around corners?

Answer: Diffraction

Diffraction allows waves to bend around obstacles and spread out through gaps.

If the amplitude of a wave is doubled, the intensity of the wave:

Answer: Quadruples

Intensity is proportional to amplitude squared (I ∝ A²), so doubling amplitude quadruples intensity.

Electromagnetic waves are arranged in the electromagnetic spectrum in order of increasing frequency. Which of the following is the correct order?

Answer: Radio → Visible → X-ray → Gamma

The EM spectrum from lowest to highest frequency: Radio, Microwave, Infrared, Visible, UV, X-ray, Gamma.