The document discusses the photon theory of light and its history. It describes Galileo and Roemer's early attempts to measure the speed of light and how Roemer observed Io to determine the speed was finite. It introduces photons as elementary particles that have properties of waves and particles, with a constant speed of 3x10^8 m/s. Einstein helped revive the particle theory of light and introduced the photoelectric effect to explain light's interaction with matter.

2. PHOTON THEORY
OF LIGHT

3. OBJECTIVES:
• Relate the atomic spectra to the photon theory of light
• Describe the relationship between the energy of the photon and
its frequency
• Explain certain phenomena using the photon theory
• Apply speed- wavelength- frequency relationship in problem
solving
• Describe the attempts of Galileo and Roemer to measure the
speed of light

4. SPEED OF LIGHT
Galileo Galilei
•One of the scientists who tried to measure the speed
of light
•Believed that light have speed
•Designed an experiment to measure the speed of
light

5. OLE ROEMER
•Danish astronomer who also attempted to measure
the speed of light
•Very keen in observing Io (Jupiter’s moon)
❖Was been observed of having a
black shadow or eclipse casted by it
❖Makes a complete orbit around
Jupiter for 1.76 days (or 1 day,18
hours, and 14 minutes)

6. ELECTROMAGNETIC
SPECTRUM
NOTE: All electromagnetic waves
travel in a vacuum at a constant
speed of 3x 𝟏𝟎𝟖 m⁄s

7. LIGHT AS A PARTICLE
ISAAC
NEWTON
• Noticed that light
casted sharp
shadows
• He thought of light
as something like
matter
• Formulated the
particle theory of
light
PARTICLE
THEORY
• Visible light is
composed of
submicroscopic
particles called
photons
PHOTONS
• These are
elementary
paticles of light
that have
properties of a
wave.

8. SOME PROPERTIES OF
PHOTONS
❖They move at a constant speed of 3 x 108𝑚⁄𝑠
❖They are massless
❖They carry energy and momentum
❖They have no charge like a neutron

9. *PARTICLE THEORY OF NEWTON
CANNOT EXPLAIN THE LIGHT
INTERFERENCE
Light
interference
Light sources
of the same
color
overlapped
light source of
different color
overlapped with
two sources of the
same color
The interaction of Light become
more intense or
brighter
New color was
correlated or produced
coherent waves
which are of the
same frequencies or
of different
frequencies

11. ALBERT EINSTEIN
- REVIVE THE THEORY OF LIGHT
INTERFERENCE
- INTRODUCED THE PHOTOELECTRIC
EFFECT
- ELECTRONS ARE EMITTED FROM A
METALLIC SURFACE WHEN SUBJECTED
TO AN INCIDENT LIGHT CONSISTING OF

12. Blackbody Radiation
•A black body is an idealized object that absorbs
all electromagnetic radiation it comes in contact
with
•The relationship between an object’s
temperature, and the wavelength of
electromagnetic radiation it emits.

14. Photoelectric Effect
a. It has a velocity of light in
free space. The velocity of
light (c) is equal to 3X108 m/s.
b. It has rest energy.
c. It has zero mass
d. It can carry energy and
momentum
e. When radiation is emitted or
absorbed, it can be created or
destroyed.
f. It can interact with other
particles like electrons

15. Photoelectric Effect
when light strikes a metal surface, the electrons would
become excited and jump out of the metal.

16. ATOMIC SPECTRUM
•Is the spectrum of frequencies of
electromagnetic radiation emitted or absorbed
during the transition of electrons between
energy levels within an atom
•Electrons that have absorbed energy jump to a
higher energy level and are said to be in an
excited state.