Today: Interference topics, intro to mechanics Exam #3 is Thursday! 1/3 millimeter Electron Microscope Image of MEMS Force Sensor
May 21, 2015
Today: Interference topics, intro to mechanics
Exam #3 is Thursday!
1/3 millimeter
Electron Microscope Image of MEMS Force Sensor
Quiz 10
(Which has more mass?)
Quiz 10
(Which has more mass?)
A carbon nucleus is stable / has significant “binding energy”
Protons and neutrons weigh LESS when bound together!
Mo
re d
ecre
ase
in m
ass
+
0
+++ 0
+
+
00 00 Carbon-12 nucleus,
Mass = 12 u (by definition)
+
0
Single free protonMass = 1.007825 u
Single free neutronMass = 1.008665 u
You need to ADD energy to takeapart a C-12 nucleus
Protons and neutrons weigh LESS when bound together!
Mo
re d
ecre
ase
in m
ass
Very significant energy releaseby fusion of deuterium / tritium
Uranium-235 decreases in mass during fission
One possible fission reaction is:
U-235 + neutron Ba-141 + Kr-92 + 3 neutrons
Ending mass = 99.9% of starting mass0.1% Missing mass = kinetic energy of products
(and some gamma rays)
Fission of 1000 kilograms of Uranium-235 releases 1 kilogram of mass energyEquivalent to a few days of U.S. electrical needs
(true: free neutrons do increase in mass)
Clicker question—Mass energy available
Which reaction can potentially release more energy per nucleon
A) More energy can be released per fission event
B) More energy can be released per fusion event
Immediately, Nuclear Fusion was recognized as an even greater source of energy
High mass atoms can yieldenergy via nuclear fission
Low mass atoms can yieldenergy via nuclear fusion
Energy availablefrom U-235
Energy availablefrom
hydrogen fusion
And of course, hydrogen is a very abundant element!
Remember to study quizzes for exam!
One topic that we will cover is diffraction and interference of light. Let’s review a little by looking at applications.
Laser Diffraction Demo (Repeat)
LaserLens
Diffraction Grating
Lens Interference patternon wall
Laser Light
Clicker Question--Diffraction
What kind of diffraction grating are we using right now?
A) Single-slitB) Double-slitC) PinholeD) Multiple slit grating
Clicker Question--Diffraction
I’m going to show you the pattern from two different apertures.
Which of the single-slit apertures is narrower?
A) First oneB) Second one
Laser Diffraction Demo (Repeat)
Different diffraction gratings produce different interference patterns
Changeable gratings allow for changeable (“dynamic”) interference
Holographic optical tweezers
Interferometric lithography
LaserLens
Diffraction Grating
Lens Interference patternon wall
Laser Light
Holographic Optical Tweezers for Biology
LaserLens PROGRAMMABLE
Diffraction Grating(e.g. LCD)
To Microscope,Creating optical tweezers
Changing deflection oflaser beams
You know more physics now about optical tweezers
You know more physics now about optical tweezers
Focused laser beam
Light hasmomentum!
Small plastic beada little lens!
If bead moves left, laser is refracted leftequal and opposite force on bead to the right
If bead moves right, laser is refracted rightequal and opposite force on bead to the left
Newton’s third law: every force has an equal force in the opposite direction
Arthur La Porta, U. Maryland
Can “unzip” DNA double helix with optical tweezers!
Requires about 15 piconewtons to unzip DNA
This is less than one trillionth the force required to lift your body! (About 1,000 Newtons)
F
F
1 2...j
3 “microns”
Can “unzip” DNA double helix with optical tweezers!
Using optical tweezers,we can find where proteins arealong a single DNA molecule!
Our lab is currently working to unzip DNA molecules extracted from living cells!
F
F
1 2...j
With protein
Without protein
Protein
Brainstorming exerciseWhat are possible uses of optical tweezers?
“Knitting DNA” http://www.youtube.com/watch?v=v97MesU3Zkw&feature=related
Video game http://www.youtube.com/watch?v=jCdnBmQZ6_s&feature=related
You also have learned physics relevant to the microelectronics industry
Photons have energy & can catalyze chemistry
Diffraction effects—diffraction limits how small we can go
Interference effects
Microelectronic circuits are made by photolithography
Using specific masks and multiple steps, make millions of tiny transistors and wires
http://www.youtube.com/watch?v=BcBNl1cfEis
Smaller features = better computerLimited by diffraction of light!
Original Mask Tolerable Diffraction Too much diffraction
Interferometric Lithography at UNM (CHTM)
Porous nanochannels made by CHTM folks
These are about 500 nm nano channels (edge-on), whose walls are made of silica nanoparticles, and thus porous.
These bright dots are images of lambda DNA in CHTM porous nanochannels. The channels are too big (>500 nm) to stretch them out.
Brueck group, CHTM
Fluorescent DNA in nanochannels
Clicker Quesiton--Diffraction
Single-slit diffraction: For a given single-slit width, which will have a wider spread in the output beam?
A) Low frequency / long wavelength (e.g. red light)
B) High frequency / short wavelength (e.g. UV light)
C) Doesn’t matter
Clicker Quesiton--Diffraction
Single-slit diffraction: For a given single-slit width, which will have a wider spread in the output beam?
A) Low frequency / long wavelength (e.g. red light)B) High frequency / short wavelength (e.g. UV light)C) Doesn’t matter
This is why the industry has moved from visible light to “deep-ultraviolet” (DUV) light for photolithography
Also: Extremely sensitive (and expensive) machines for placing mask very very close to the wafer
The same process for making Pentiums can be used to make tiny machines
Microelectromechanical Systems (MEMS)
Dust Mite(GROSS!)
MEMS Gear
Electron micrsocopy image
We are using MEMS for biophysics applications-> Measuring tiny forces
1/3 millimeter
Electron Microscope Image of MEMS Force Sensor
Hooke’s Law for Springs
F = k * x
Force is proportional to stretch of spring
“k” is called the “spring constant” in units of Newtons / meter
Relationship is violated frequently (think plastic, silly putty, etc.)
We used the tiny spring to weigh tiny things
30 micron plastic beadsWeight = 100 piconewtons
Typical human hair for comparison
Force = k * spring displacement
k = 1 piconewton per nanometer
We used the tiny spring to weigh tiny things
Direction ofGravity 300 pN
Wieght standard beads areout of field of view on otherset of gratings
Direction of gravity
Force = k * spring displacement
k = 1 piconewton per nanometer
“Mechanics”
Mechanics is the physics of how everyday objects move and respond to forces.
It was the first well developed field of physics.
Mathematics are key to mechanics, making the physics extraordinarily powerful (but not simple).
We are skipping most of mechanics because we don’t have access to the mathematical tools.
FORCE…Brainstorming
What can forces do?
FORCE…What is a force?
What can force do?
Force changes the motion of an objectgravitational force is responsible for the
elliptical orbit of the Earth / Sun.
frictional force slows down a sliding hockey puck.
Force causes deformations in an objectelectrical force causes nucleus to deform
applied force can cause a spring to stretch or compress
FORCE…What is a force?
What kind of forces are there?
Fundamental: Gravity, Electromagnetic, strong, weak
Practical: Gravitational, electrical, magnetic, frictional, drag “stretchy”, contact (hard objects)
All of these can be measured in units of “force”
Pounds or Newtons are common. 2.2 lbs. =~ 10 Newtons.(1 kg weighs 10 Newtons on Earth)
Clicker Question—units of force
Which of these is closest to the equivalent of 1000 newtons of force?
A) 22,000 poundsB) 2,200 poundsC) 1,200 poundsD) 220 poundsE) 22 pounds
Clicker Question—units of force
Which of these is closest to the equivalent of 1000 newtons of force?
A) 22,000 poundsB) 2,200 poundsC) 1,200 poundsD) 220 poundsE) 22 pounds
A 220 pound person weighs 1000 newtons.(The mass would be 100 kilograms)
Newton first formalized mathematics of forces
Scientists had been thinking about force and motion for centuries before Newton…read about it in the textbook!
Newton’s three laws of motion
http://www.youtube.com/watch?v=9EIZo9egyL4
Newton’s first law of motion.
Also called the law of inertia.
An object will continue in a state of rest or uniform motion unless acted upon by an external force
“If it doesn’t fit, you must acquit!”
“If no force exists, the motion persists!”
Because of friction and air resistance, there is no obvious demonstration that Newton’s first law is exactly true!
This is a key part of why the law was not obvious to those before Galileo and Newton (Aristotle)
Newton’s second law of motion. (fudged a little bit)
“Change in motion is directly proportional to the force acting on the object.”
“Acceleration is proportional to force”
acceleration = force / massa = f / m
Force = mass x acceleration
F = m aThe TA, Katie, found this to help you remember:http://www.youtube.com/watch?v=dQmYBF_Sd8I&feature=related
Lecture ended here (after F=ma video)