Transcript Unit 3 EMR 2015

Physics 30 Unit 3 EMR
Maxwell’s 4 Principles of EMR:
•A current carrying conductor surrounds itself with a
circular ____________field.
magnetic
(Oersted)
•A conductor that cuts through magnetic field lines will
have a ________
current induced through the conductor. (Faraday)
Lenz’s Law applies whenever a current is
𝐹𝑚 𝑜𝑝𝑝𝑜𝑠𝑒𝑠 𝐹𝑎
produced in this way: _________________
electric field produces a
•A changing _______
magnetic field.
changing _________
∆𝐸
magnetic field produces a
•A changing __________
changing ____________
field.
electric
∆𝐵
∆𝐸
end
Propagation of EMR:
•Maxwell’s principles can be summarized by:
•The electric field is ____________
perpendicular to the magnetic field.
•The magnetic field is ____________
perpendicular to the electric field.
•Both the electric and magnetic fields are ______________
perpendicular to the
direction the EMR wave travels.
•EMR travels at ________________
the speed of light in air or a vacuum.
•Even though EMR is made up of ________
magnetic fields,
electric and ________
it is not deflected by __________
electric or __________
magnetic fields. Only
charged particles are deflected by those fields.
end
Production of EMR:
•Most EMR is produced by accelerating ___________.
charges
EMR Spectrum:
Low energy
High energy
Large wavelength
Small wavelength
Small frequency
Accelerating charges
High frequency
Oscillating
molecules
e- transitions
in atoms
ROYGBIV
High speed
e- stopped
Nuclear
decay
e- transitions
in atoms
700 nm in air
400 nm in air
end
Properties of EMR:
•Radio Waves and Microwaves: produced by accelerating
___________
electrons between electric plates. Used for
communication and a particular part of the microwave
________________
heating
spectrum is used for __________.
•Infrared Waves: are produced by __________
vibrating atoms and
molecules within matter. Transfers _______
heat between
objects.
•Visible Light: produced as objects reach a certain
temperature. The visible light spectrum is ROYGBIV
________ with
violet light having a wavelength of __________
around 400 nm and red
around 700 nm in air.
light ___________
end
Properties of EMR:
electrons across a high
•X-Rays: produced by accelerating _________
potential difference and then ________
stopping them suddenly. All
kinetic energy of the electrons is converted into
the ________
medical imaging
EMR. Used for _______________.
Formulas for X-Rays:
High speed electrons are stopped so conservation of energy is used:
Ee- = Ex-ray
½mv2 = Vq = hc/l = hf
•Gamma Rays: is a product of radioactive
_________ decay. They
have a very _______
short wavelength, very ______
high frequency.
Can cause cell __________
mutations and cancer. Very dangerous
and require lots of shielding for protection.
end
Duality Theory of LIght:
wave and a _________.
particle
•Light can be thought of as both a ______
•Wave Theory: Light travels as a wave through a medium
________
like air, water, glass…
Young’s
•____________
double slit experiment provided evidence
for the wave nature of light.
Polarization also
•____________
shows that light behaves
like a wave. Particles
should go through the slits
in a polarizing filter.
Waves can be stopped by
rotating
____________the
polarizing filter.
end
Polarization:
end
Quantum (Particle) Theory: Light travels as a tiny bundle of energy in
the vacuum of space.
•Newton used particle theory to explain refraction. He thought light
consisted of particles with _______.
mass As the particles travelled from
one medium to another they experienced a different force from the
surrounding particles, resulting in the bending of the beam of light.
His theory also (incorrectly) predicted that the light particles would
____________
speed up
as they travelled into a medium with a higher “n”
value. As a result, refraction is best explained using ______properties.
wave
•___________
Einstein’s photoelectric effect provided evidence for the
particle (quantum) theory of light.
•The _________
Compton effect also provided evidence for the
particle nature of light. He showed that EMR could transfer
_____________
momentum to electrons.
end
Einstein’s Photoelectric Effect: The Formula
𝐸𝐸𝑀𝑅 = 𝑊 + 𝐸𝑒−
metal
ℎ𝑓
1
𝑉𝑞 𝑜𝑟 𝑚𝑣 2
2
ℎ𝑐
𝑜𝑟
𝜆
ℎ𝑓𝑜 𝑜𝑟
ℎ𝑐
𝜆𝑚𝑎𝑥
end
Photoelectric Effect: Graphing
𝐸𝐸𝑀𝑅 = 𝑊 + 𝐸𝑒−
𝐸𝐸𝑀𝑅 − 𝑊 = 𝐸𝑒−
𝑚𝑥 + 𝑏 = 𝑦
Energy of e(x10 -? J)
or
(x10? ev)
Work
Function
Slope usually equals
Plank’s constant
Frequency (f) or Wavelength (l)
Threshold
frequency (f0)
end
•Einstein’s Photoelectric Effect: Theory
If a green photon emits an 𝑒 − because its energy is just above the
work function of the metal, will red and violet photons also
release 𝑒 −
metal
No for red
Yes for violet
end
•Einstein’s Photoelectric Effect: theory
Green photon emits 𝑒 − . Will changing to violet light release:
A) more 𝑒 −
B) less 𝑒 −
C) the same # of 𝑒 −
metal
The same number. It’s a one to one relationship.
end
•Einstein’s Photoelectric Effect: theory
Green photon emits 𝑒 − . Will increasing the number of green
photons:
A) increase the number of 𝑒 − released?
B) give the 𝑒 − more kinetic energy?
C) require more voltage to stop
the 𝑒 −
Increased intensity
metal
A) Each photon releases an e- so more photos = more
electrons which will increase the current produced.
end
Einstein’s Photoelectric Effect: theory
•If incident EMR has enough energy to free electrons from a
metal, it will.
•_______
one
EMR photon will release _____
one electron
•Increasing the intensity of the light (number of photons /
brightness) will release more ___________,
increasing current.
electrons
•Increasing the energy of the light (higher frequency/ shorter
wavelength) will release the same amount of electrons, but they
voltage to
will be moving with more energy requiring more _________
stop them.
end
•Compton Effect: The Formula
the scattered x-ray has
less energy (longer
wavelength)
mass of an 𝑒 −
end
•Compton Effect: Conservation of Energy
To solve the speed of the electron, use conservation of
energy. It’s a scalor, so you can ignore direction.
0
Ex-ray + Ee- = Escattered + Ee-
end
•Compton Effect: Conservation of Momentum
To solve the angle of deflection of the electron, use
conservation of momentum because it’s a vector.
Horizontal
0
Px-ray + pstationary e- = pscattered + peVertical
0
Px-ray + pstationary e- = pscattered + pe-
end
•Compton Effect: Conservation of Momentum
Horizontal
𝑝
=
=
𝑝′
Vertical
𝑝
=
0
=
𝑝′
end
Properties of EMR:
Reflection:
qi = qr
•The reflection law is summarized as: ________________
qi
qr
•Remember that all the angles in a triangle add up to
_______
1800 degrees.
•Both ___________
particles
and ____________
waves
reflect.
end
Refraction:
•Is the _________
bending of light as it passes from one medium to
another. When light goes from one medium to another, its
angle , _______
speed and __________
wavelength all change, while
______
frequency remains the same.
wave
•Refraction is a _____________
property..
optically denser
material
“n” has increased
optically less
dense material
“n” has decreased
end
Refraction:
•Snell’s Law is used for refraction questions:
•Example:
Notice that the “n” values are flipped.
This means an opposite effect will occur
600 nm
400
air
n=1.40
Because “n” increased, the refracted
angle, speed and wavelength will all be
smaller.
Frequency is missing from the formula. It
remains constant.
end
600 nm
400
air
n=1.40
Frequency remains constant
end
Refraction:
•Total Internal Reflection & Critical Angles:
•Example:
qc
n=1.80
n=1.25
end
Prism Question:
600
260
730
170
air
470
430
430
470
170
730
Error! Light ray internally reflects.
600
Equilateral
triangle
n=1.50
end
Dispersion:
•Is the _________
Separating out of light into it’s colours as it passes
through a medium – like in a prism. Visible light can
ROYGBIV
separate into it’s component colours ___________.
Red refracts rotten
Diffraction:
•Is the _________
bending of light around objects or the edges of
barriers. The ___________
diffracted waves can interfere with each
other either _____________
constructively or _______________.
destructively
Visible light can separate into it’s component colours like
VIBGYOR
dispersion, but the colours are reversed: _________
Red diffracts more
end
Diffraction Gratings:
•Light travelling through a grating with tiny slits diffracts.
The bent waves interfere constructively and destructively
to form bright ________
and dark ________
on a screen
lines
bands
behind the grating.
Can only be used
if the angle is less
than 10 degrees!!
end
Diffraction Gratings:
n=3
n=2
𝑥
n=1
𝜃
𝜆
laser
𝑙
n=1
diffraction grating (d)
n=2
screen
n=3
end
Spectrums:
lined patterns caused by light passing through
•The _______
diffraction gratings can be used to identify elements giving
off the light.
•An ____________
absorption spectrum is the pattern caused by light
being passed through a _____________
cool (unexcited) gas. Certain
wavelengths are absorbed, creating _________
dark bands_in the
pattern.
•An ___________
emmission spectrum is the pattern caused by light
from a ____________
hot (excited) gas. Certain wavelengths are
released by the element(s) in the gas, creating
bright lines in the pattern.
_____________
end
Refraction
Diffraction and Interference
Red
refracts
rotten
Blue will
refract
more
Red will
experience a
greater
diffraction angle
Blue will
experience a
smaller
diffraction angle
end
Graphing diffraction grating experiment:
Problem: Calculate the wavelength of monochromatic light
Manipulated Variable: the distance between the grating and the screen.
Responding Variable: the distance between the center and n (you
decide which to use)
Controlled Variables: the bright line number you chose (n)
the diffraction grating (d)
Distance
between the
center bright
line and “n”
(x)
Distance between grating and
screen (𝑙)
end
Distance
between the
center bright
line and “n”
(x)
Slope =
𝑥
𝑙
Distance between grating and
screen (𝑙)
𝑥𝑑
𝜆=
𝑛𝑙
𝑑 sin 𝜃
𝜆=
𝑛
Which
applies?
𝑥
Test the angle using: tan 𝜃 =
𝑙
end
Speed of EMR:
Formulas:
Experiments:
time
Galileo: couldn’t measure the ___________
it took light to
travel from one hilltop to another.
time
Romer: used the ________
difference observed for Io (moon)
to orbit Jupiter. The orbital time was different because of
Earth’s orbit around the sun.
Earth’s orbital radius
Time difference observed
end
Speed of EMR (experiments):
Fizeau: used a rotating mirror apparatus to measure the speed
of light. He found that the speed of light was slower in
__________
than in air. This disproved Newton’s particle
water
model, which predicted that light would speed up in an
“optically denser” medium.
Tube filled with
water.
Steam driven
rotating mirror
(about 800 rev/s)
light source
air
water
Speed of EMR (experiments):
Michelson: used a multi-sided (8) rotating mirror to measure
the speed of light very accurately. You need to know the
mathematics behind this experiment.
Where:
Distance is to mirror and back (x2)
Time is obtained from the # of
sides and frequency of rotation:
T=1/f and then divide by # of sides.
end
Mirrors:
Plane Mirror:
qi = qr
•The __________________
Reflected objects are:
qi
qr
Reversed (left/right)
________________________
hi = ho
________________________
di = - do (in behind the mirror)
________________________
virtual
________________________
end
Concave Mirror:
converging mirrors
• Also called ____________
• Have a positive focal length (f= +)
Converging Lens:
• Also called ___________
double convex
lens.
• Have a positive focal length.
inverted
real
larger
• Images are ____________,
________,
and get ___________
as the
object approaches the mirror/lens.
focal
• No image formed when object is placed at the ____________
point.
• When object is between the focal point and the mirror/lens, the
image is __________,
___________
and ___________.
upright
larger
virtual
end
Convex Mirror:
diverging
• Also called ____________
mirrors
• Have a negative focal length (f -)
Diverging Lens:
• Also called ___________
double concave
lens.
• Have a negative focal length.
smaller
virtual
• Images are always ____________,
______________,
and
_________________.
upright
end
Mirror Formulas:
Examples:
•A 8.00 cm tall object is placed 22.0 cm in front of a convex
mirror that has a focal length of 7.00 cm. What are the
characteristics of the image?
hi=+1.93 cm
Image is virtual
Image is upright
end
Examples:
•A 7.00 cm tall object is placed 5.00 cm in front of a
converging lens that has a focal length of 4.00 cm. What
are the characteristics of the image?
hi=-28cm
Image is real
Image is larger and
inverted
end
Graphing mirror/lens questions:
sin q
sin q
Finding the Critical Angle:
l
𝜆
𝜆
𝑠𝑙𝑜𝑝𝑒 = =
sin 𝜃
sin 𝜃
Which is 900 ?
l
end
1/di
Rearrange into y=mx+b
𝑦 =𝑚𝑥+𝑏
1/do
1
1 1
=− +
𝑑𝑖
𝑑𝑜 𝑓
1
𝑓
is the y-intercept
end