Sound and Optics

MCAT Prep: Physics and Math Part 5

Sound

propagates through a deformable medium by the oscillation of particles parallel to the direction of the wave’s propagation

Intensity

P/A

SI units: W/m²

Sound level

(β) = 10 log (I/I₀)

Unit: decibel = dB

10

An increase of 10 dB is an increase in intensity by a factor of ______

100

An increase of 20 dB is an increase in intensity by a factor of ______

Doppler Effect

when a source and a detector move relative to one another, the perceived frequency of the sound received differs from the actual frequency emitted

f’ = f [(v±v_D)(v±v_S)]

Stationary source

v_s = 0

Stationary detector

v_D = 0

closer

Observer and detector moving ________:

• + sign in numerator

• - sign in denominator

apart

Observer and detector moving ________:

• - sign in numerator

• + sign in denominator

Refraction

n = c/v

3 × 10^8 m/s

speed of light

Snell’s law

n₁ sin θ₁ = n₂ sin θ₂

toward

When n₂ > n₁, light bends ________ the normal

away

When n₂ < n₁, light bends ________ the normal

Converging system

convex lens, concave mirror

f > 0

Convex

Concave

Mirrors (+)

Focal length (f): concave (converging)

Object distance (o): real object (in front of this)

Image distance (i): real image (in front of this)

Magnification (m): upright image

Mirrors (-)

Focal length (f): convex (diverging)

Object distance (o): virtual object (behind this)

Image distance (i): virtual image (behind this)

Magnification (m): inverted image

Lens (+)

Focal length (f): convex (converging)

Object distance (o): real object (in front of this)

Image distance (i): real image (in front of this)

Magnification (m): upright image

Lens (-)

Focal length (f): concave (diverging)

Object distance (o): virtual object (behind this)

Image distance (i): virtual image (behind this)

Magnification (m): inverted image

o > 2f

real, inverted, reduced image

o = 2f

real, inverted, same image

2f > o > f

real, inverted, magnified image

o = f

no image

o < f

virtual, upright, magnified image

all o distances

virtual, upright, reduced image

Diverging system

concave lens, convex mirror

f < 0

1/f = 1/o + 1/i

Magnification

-i/0

P = (1/f)(D = m^-1)

reduced

|m| < 1 image _________

enlarged

|m| > 1 image _________

same size

|m| = 1 image _________