Warm Up 3-23
1. If I am looking in a mirror and my reflection is
larger than me, which type of image is this?
2. When light passes through the lens of your eye,
it is projected upside-down in your retina, this is
called a(n) ______________ image.
3. Draw an image of an eyeball with imperfect
vision
Dual Nature of Light
Light is unique because it has properties of
BOTH waves and particles
Historical Evidence
The Double Slit
Experiment:
-Done by
Thomas Young in 1801
-Showed that
light acts like a wave
Historical Evidence
The Double Slit
Experiment:
Light sent through two
openings showed
interference with each
other on the wall behind
Interference is only seen
with waves
Historical Evidence
The Photoelectric
Effect
-Discovered by
Albert Einstein in 1921
-Showed that
light acts like a particle
Historical Evidence
The Photoelectric
Effect
-When light hits metal,
it causes the release of
electrons
-This is a physical
interaction that only
particles can do
The Photoelectric Effect
• The photoelectric effect is caused by photons
which are light particles
• Photons will collide
with a surface and
knock electrons off of
the material as long as
they have enough energy
The Photoelectric Effect
• The energy of a wave or photon is determined
by the light’s frequency (the energy and
frequency are directly proportional)
Electromagnetic
Spectrum
Energy of a Photon
The energy of a photon can actually be
calculated using this equation:
E = hf
E – energy of photon (J)
h – Plank’s constant = 6.62607004 × 10-34 m2kg/s
f – frequency (in Hz)
Electromagnetic
Spectrum
Using a light that has a higher frequency will
cause electrons to eject at higher speeds
Increasing the intensity (brightness) of the light
will cause more electrons to eject
Dim light
Bright Light
Does light act like a wave or a
particle?
Both!
Who discovered that light acts
like a particle?
Einstein!
Which type of wave is the
highest energy?
Electromagnetic
Spectrum
Gamma!
Who discovered that light acts
like a wave?
Young!
What determines the energy of
an electromagnetic wave or a
photon?
Frequency!
What color of visible light will eject
electrons with the greatest speed?
Electromagnetic
Spectrum
Violet!