Chapter 7: Light

Electromagnetic Wave

Fig 7.2

• Electromagnetic Radiation• Both “fields” vary together• Transverse Waves.

• Electromagnetic Radiation• Both “fields” vary together• Transverse Waves.

Electromagnetic (EM) Spectrum

Fig 7.3• Range of Frequencies (or Wavelengths)

• Visible Light only a small portion.

• Range of Frequencies (or Wavelengths)

• Visible Light only a small portion.

Sources of Light

• Matter constantly emits and absorbs radiation

• Emission mechanism: – Accelerated, oscillating “charges” produce EM Waves

• Different accelerations lead to different frequencies

• Key Terms: Luminous and Incandescent.

• Matter constantly emits and absorbs radiation

• Emission mechanism: – Accelerated, oscillating “charges” produce EM Waves

• Different accelerations lead to different frequencies

• Key Terms: Luminous and Incandescent.

Blackbody Radiation

• “Blackbody”– Idealized material– Perfect emitter ; perfect absorber

• Increasing Temperatureresults in?...

• Spectrum of Sun light.

• “Blackbody”– Idealized material– Perfect emitter ; perfect absorber

• Increasing Temperatureresults in?...

• Spectrum of Sun light.

Fig 7.4Fig 7.5

Properties of Light: Two “Models”

“Light Ray” Model• Particle-like view• Photons travel in

straight lines• Best explains – Mirrors– Prisms– Lenses

“Light Ray” Model• Particle-like view• Photons travel in

straight lines• Best explains – Mirrors– Prisms– Lenses

“Wave” Model• Traces motions of

wave fronts• Best explains– Interference– Diffraction– Polarization

“Wave” Model• Traces motions of

wave fronts• Best explains– Interference– Diffraction– Polarization

http://hyperphysics.phy-astr.gsu.edu/hbase/ligcon.html#c1

Light interacts with matter

Fig 7.6• Interaction begins at the surface and depends upon?

• Possible Interactions?

• Transparent vs Opaque?

• Interaction begins at the surface and depends upon?

• Possible Interactions?

• Transparent vs Opaque?

Reflection

ri

Fig 7.11

Diffuse Reflection

Fig 7.7Fig 7.10

Why is the sky blue at noon?(A Closer Look)

Another Behavior of Light

Refraction

• Light crossing a boundary surface and changing direction (bending)

• Reason?– Differing densities.

• Light crossing a boundary surface and changing direction (bending)

• Reason?– Differing densities.

Fig 7.15

ri

Magnitude (Amount)of Refraction

• Depends upon?:1. Angle which light strikes

the surface2. Ratio of the speeds of

light in the two materials

• #2 helps define the Index of Refractionof a substance

• Depends upon?:1. Angle which light strikes

the surface2. Ratio of the speeds of

light in the two materials

• #2 helps define the Index of Refractionof a substance

Table 7.1

Example 7.1

Mirages

Similar to Fig 7.17

“Mirage” is due to Refraction!

Wet Highway?Wet Highway?

Dispersion and Colors

• White light

• Dispersion (Spreading)

• Wavelength and frequencyare related

• White light

• Dispersion (Spreading)

• Wavelength and frequencyare related

Dispersion and Colors

Rainbows (A Closer Look)

Fig 1.15

Box Fig 7.7

OpticsThe use of lenses to form images

• Concave lenses– Diverging

• Convex lenses– Converging

• Concave lenses– Diverging

• Convex lenses– Converging

BOX FIG 7.1

The Human Eye

Nearsightedness (myopia) Nearsightedness (myopia) corrected with a:corrected with a:

Nearsightedness (myopia) Nearsightedness (myopia) corrected with a:corrected with a:

Farsightedness (hyperopia) Farsightedness (hyperopia) corrected with a:corrected with a:

Farsightedness (hyperopia) Farsightedness (hyperopia) corrected with a:corrected with a:

Concave LensConcave Lens

Convex Lens.Convex Lens.

BOX FIG 7.4

Uses a convex lens to Uses a convex lens to change focal lengthchange focal lengthUses a convex lens to Uses a convex lens to change focal lengthchange focal length

The nature of lightWave-like behavior

Diffraction & InterferenceDiffraction & Interference

Fig 7.19

Wave-like behavior - Polarization

• Alignment of electromagnetic fields

• Unpolarized vs. Polarized light

(Figs 7.20 and 7.21)

• Alignment of electromagnetic fields

• Unpolarized vs. Polarized light

(Figs 7.20 and 7.21)

The nature of light:Particle-like behavior

“Quanta” and Photons“Quanta” and Photons

Example 7.3

Photoelectric Effect

Fig 7.23

Next: Chapter 8

Atoms and the

Periodic Properties