The document summarizes key concepts about the particle and wave properties of light. It discusses (1) Newton's corpuscular theory of light and the establishment of the wave theory by Huygens, (2) wave phenomena such as reflection, refraction, diffraction and interference, (3) the photoelectric effect and how Einstein's photon theory explained experimental observations, and (4) provides an example calculation of determining the work function of a metal from photoelectric emission data.

1. Particle Properties
of
Waves

2. LIGHT
WAVES vs PARTICLE

3. The Corpuscular Theory
• Newton: light consists of streams
of tiny particles, which he called
“corpuscles”.
• Rectilinear Propagation
• Reflection
• Refraction

4. The Wave Theory
• Christian Huygens : the wave nature of
light was firmly established
• Interference
• Diffraction

5. Rectilinear Propagation
Wave fronts - The portions of water surface whose particles that are all
in the same phase of motion.
*The direction of propagation of the advancing
straight wave is perpendicular to the wave front.

6. Reflection
A wave is turned back, or reflected, when it
encounters a barrier that is boundary of the
medium in which the wave is traveling.

7. Reflection
I and r is 0 degree when the incident wave
approaches the barrier along a line
perpendicular to it.

8. Reflection
Law of Reflection:
i=r
When a wave disturbance is reflected at the
boundary of a transmitting medium, the angle of
incidence is equal to the angle of reflection.

9. Reflection

10. Refraction
The bending of the path of a wave disturbance
as it passes obliquely from one medium into
another of different propagation speed.

11. Refraction
Water waves travel faster on
the surface of deep water
than they do on shallow water.
The change in speed of the wave will
cause refraction. The slower wave in the shallow
water has a smaller wavelength.

12. Refraction

13. Diffraction
Spreading of a wave disturbance beyond the
edge of a barrier.
Set-up: Place two straight barriers across the
tray on a line parallel with the straight way
generator. An aperture, or opening, is left
between them approximately equal to the
wavelength of the wave to be used. As a
segment of each wave crest passes through the
aperture, it clearly spreads into the region
beyond the barriers.

14. Diffraction
The diffraction of a periodic straight wave as it
passes through a small aperture. Observe the
decrease in the diffraction effect as the
wavelength of the disturbance sent against the
barrier is shortened.

15. The Superposition Principle
When two or more waves travel
simultaneously through the same medium,
(I) each wave proceeds independently as
though no other waves were present and
(2) the resultant displacement of any
particle is the vector sum of the
displacements that the individual waves
acting alone would give it.

16. The Superposition Principle
Y1- black solid line
Y2- black dashed line
Y- red line
In effect, the displacement of any particle of the medium
by one wave at any instant is superimposed on the
displacement of that particle by the other wave at that
instant. The action of each wave on a particle is
independent of the action of the other, and the particle
displacement is the resultant of both wave action.

17. Interference
The general term interference is used to
describe the effects produced by two or
more waves that superpose while passing
through a given region.

18. Interference
Constructive Interference
-suppose the displacement of a particular particle caused by one
wave at any instant is in the same direction as that caused by the
other wave. Then the total displacement of that particle at that
instant is the sum of the separate displacements (superposition
principle). The resultant displacement is greater than either wave
would have caused separately.

19. Interference
Destructive Interference
-if the displacement effects of the two waves on the particle are in
opposite directions, they tend to cancel one another. The resultant
displacement of that particle at that instant is the difference of the
two separate displacements and is in the direction of the larger
(superposition principle). The resultant displacement is less than
one of the waves would have caused separately.

20. Interference
Complete destructive interference
If two such opposite displacements are equal in
magnitude, the resultant displacement is zero. The
destructive interference is complete. The particle is not
displaced at all but is in it’s equilibrium position at that
instant.

22. Electromagnetic Waves
A periodic disturbance involving
electric and magnetic force. They are all the
same kind of wavy disturbance that repeats
itself over a distance called the wavelength.

23. Electromagnetic waves

24. Electromagnetic Waves

25. Electromagnetic waves
The ELECTROMAGNETIC SPECTRUM is the range
of all possible frequencies of electromagnetic radiation
. The "electromagnetic spectrum" of an object is the
characteristic distribution of electromagnetic radiation
emitted or absorbed by that particular object.

26. Electromagnetic waves

27. The Photoelectric Effect
The emission of electrons by a
substance when illuminated by
electromagnetic radiation.

28. The Photoelectric Effect
The photoelectric effect was accidentally
discovered by Heinrich Hertz in 1887
during the course of the experiment that
discovered radio waves.
Observation: when a negatively charged
body was illuminated with light, its charge
was diminished.

29. The Photoelectric Effect
J.J. Thomson and P. Lenard determined the
ratio e/m for the particles emitted by the body
under illumination – the same as for electrons.
The effect remained unexplained until 1905
when Albert Einstein postulated the existence
of quanta of light -- photons -- which, when
absorbed by an electron near the surface of a
material, could give the electron enough energy
to escape from the material.

30. The Photoelectric Effect
Robert Milliken carried out a careful set
of experiments, extending over ten years,
that verified the predictions of Einstein’s
photon theory of light.

33. The Photoelectric Effect

34. The Photoelectric Effect
Observations:
• For a given material of the cathode, the “stopping” voltage does not
depend on the light intensity – the energy of photons is
determined by the light frequency, not intensity
• The saturation current is proportional to the intensity of light at f
=const – the saturation current is proportional to the number of
photons, thus to the light intensity
• Material-specific “red boundary” f0 exists: no photocurrent at f < f0 –
at f < f0 (hf < W) the photon energy is insufficient to extract an
electron from metal

35. The Photoelectric Effect
It takes a certain amount of energy for an
electron to escape from the metal.
Electrons absorb this energy from the light
Light is made up of photons with a certain
amount of energy given by
E = hf
h = planck’s constant (6.63x10^-34)
f = frequency

36. The Photoelectric Effect
Energy of the photon goes into:
1. work function – work to free the electron
2. kinetic energy of the electron

37. The Photoelectric Effect
Sample Problem:
Radiation with a wavelength of 200 nm
strikes a metal surface in a vacuum.
Ejected electrons have a maximum speed
of 7.22x10^5 m/s. What is the work
function of the metal in eV?

38. The Photoelectric Effect
Given:
h (planck’s constant) = 6.63 x 10^-34
wavelength= 200 x 10^-9 m
Speed (v) = 7.22 x 10^5 m/s
m (mass of electron) = 9.1 x 10^-31 kg

39. The Photoelectric Effect
f= speed of light
wavelength
f = 3 x 10^8 m/s
200 x 10^-9 m
= 1.5 x 10^15 Hz

40. The Photoelectric Effect
(6.63 x 10^-34 J.s) 1.5 x 10^15 Hz = W + ½ (9.1 x 10^-31 kg)(7.22 x 10^5 m/s)^2
9.94 x10^-19 J = W + 2.37 x 10^-19 J
(9.94 x 10^-19 J) – (2.37 x 10^-19 J) = W
W = 7.57 x 10^ -19 J
(7.57 x 10^-19 J) x 1ev = 4.73 eV
1.6 x 10^-19 J

41. Prepared by:
Maria Criselda V. dela Cruz
Bs Bio 2A