Lesson 2 of 15

Reflection and Mirrors

Reflection and Mirrors

The law of reflection states that when light bounces off a surface, the angle of reflection equals the angle of incidence, both measured from the normal to the surface:

θr=θi\theta_r = \theta_i

Spherical Mirrors

A spherical mirror has a focal point FF at half the radius of curvature RR:

f=R2f = \frac{R}{2}

  • Concave mirror (converging): f>0f > 0. Used in telescopes, headlights, and shaving mirrors.
  • Convex mirror (diverging): f<0f < 0. Used in security mirrors and car rear-view mirrors.

The Mirror Equation

The relationship between object distance dod_o, image distance did_i, and focal length ff:

1f=1do+1di\frac{1}{f} = \frac{1}{d_o} + \frac{1}{d_i}

Solving for the image distance:

di=11f1dod_i = \frac{1}{\dfrac{1}{f} - \dfrac{1}{d_o}}

Sign Conventions

QuantityPositiveNegative
dod_oObject in front of mirror(always positive)
did_iReal image (in front)Virtual image (behind)
ffConcave mirrorConvex mirror

Magnification

The lateral magnification relates image size to object size:

m=didom = -\frac{d_i}{d_o}

  • m>1|m| > 1: image is magnified
  • m<1|m| < 1: image is diminished
  • m>0m > 0: image is upright (virtual)
  • m<0m < 0: image is inverted (real)

Your Task

Implement the mirror equation and magnification formula below.

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