Physics: Optics and Waves Flashcards

A converging lens has a focal length of 20 cm. An object is placed 30 cm from the lens. Where is the image formed?

Answer: 60 cm on the opposite side of the object

Using 1/f = 1/do + 1/di: 1/20 = 1/30 + 1/di → di = 60 cm on the opposite side (real image).

Which phenomenon explains why the sky appears blue?

Answer: Rayleigh scattering of shorter wavelengths

Rayleigh scattering preferentially scatters shorter (blue) wavelengths of sunlight in all directions, making the sky appear blue.

Two waves with equal amplitude A are superimposed. If they are exactly out of phase (180°), the resultant amplitude is:

Answer: 0

Destructive interference occurs when waves are 180° out of phase, causing complete cancellation and a resultant amplitude of zero.

The critical angle for total internal reflection at a glass-air interface is 42°. What is the index of refraction of the glass?

Answer: 1.49

At critical angle: sin(θc) = n_air/n_glass → n_glass = 1/sin(42°) ≈ 1.49.

Which type of wave requires a medium to propagate?

Answer: Sound waves

Sound waves are mechanical waves that require a medium (solid, liquid, or gas) to propagate, unlike electromagnetic waves.

A plane mirror forms an image that is:

Answer: Virtual, upright, and same size

A plane mirror always produces a virtual, upright image at the same distance behind the mirror, with magnification = 1.

The wavelength of light in a medium with index of refraction n = 1.5, if the wavelength in vacuum is 600 nm, is:

Answer: 400 nm

The wavelength in a medium is λ_medium = λ_vacuum / n = 600 nm / 1.5 = 400 nm.