AP Physics 2 Unit 6

Wave Motion and Geometric Optics

Two features common to all mechanical waves

• A wave is a traveling disturbance• A wave carries energy from place to place

without transferring matter

Two types of waves

• Transverse – the disturbance is perpendicular to the direction of the motion

• Longitudinal – the disturbance is parallel to the direction of the motion

Wave terminology

• Equilibrium position• Crest and trough• Wavelength• Amplitude• Period• Frequency

Importante – the frequency of the wave is determined by the source.

The speed of the wave is determined by the medium.

Mathematical Description of a Transverse wave

Superposition of waves

Reflections of a wave at a fixed and free end.

Standing waves – demo

The electromagnetic Spectrum – no medium required

All waves of electromagnetic spectrum spectrum travel at the speed of light, c = 2.99 x 108 m/s. Note the relationship between

wavelength, frequency and energy.

The electromagnetic spectrum

• Radio (AM, FM, TV) > 30 cm• Microwaves (radar, atomic-molecular research,

m-wave ovens) between 30 cm and 1 mm• Infrared between 1 mm and 700 nm• Visible light between 400 nm and 700 nm• Ultraviolet between 400 nm and 60 nm• X-rays between 60 nm and 10 EE -4 nm• Gamma rays between 0.1 nm and 10 EE -5 nm

Electromagnetic waves are transverse waves composed of

alternating electric and magnetic fields

Polarization of Light

Let’s look at unpolarized light first

The fence and the rope

Geometric Optics

Wave Fronts and Rays

Reflection of Light

Law of Reflection

Specular (regular) and diffuse reflection

Is all of the light incident upon the mirror reflected?

Plane Mirrors

Five Properties of the image of a Plane Mirror

• Upright• Same size• Located as far behind the mirror as the

object is in front of the mirror• Left to right reversed• Virtual image

Ray Diagram for a Plane Mirror

Spherical Mirrors (concave – converging and convex –

diverging)

The focal length and radius of curvature

Ray diagrams for curved mirrors. Only two rays are needed to locate

an image• Any ray drawn parallel to the principal axis is

reflected through the focal point• Any ray drawn through the focal point is reflected

parallel to the principal axis• Any ray incident upon the mirror is reflected at

the same angle when measured from the normal• Any ray drawn through the center of curvature is

reflected upon itself

Six ray diagrams for converging (concave) mirrors

Only one ray diagram for convex (diverging mirrors)

The mirror equation and magnification (and an impressive

proof thrown in for free)

Summary of sign conventions for curved mirrors

• f is positive for a concave mirror and negative for a convex mirror

• so is positive for an image located in front of the mirror (our only concern at this point)

• si is positive for a real image (in front of the mirror) and negative for a virtual image (behind the mirror)

Ex. A 2.00 cm object is placed 7.10 cm from a concave mirror whose radius of curvature is 10.20 cm. Find the location and size of the image.

Ex. An object with a height of 1.20 cm is placed 6.00 cm in front of a concave mirror with a focal length of 10.0 cm. Find the location and height of the image.

Ex. An object is placed 66 cm in front of a convex mirror that has a focal length of 46 cm. Find the image distance and magnification.