electric forces & fields chapter 18. the origins of electricity in the mid 18 th century ben...
TRANSCRIPT
![Page 1: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/1.jpg)
Electric Forces & Fields
Chapter 18
![Page 2: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/2.jpg)
The Origins of Electricity
• In the mid 18th century Ben Franklin created the idea on positive and negative electric charge.
• It wasn’t until 150 years later the electron was discovered.
• Franklin described an electric “fluid” that would flow depending on electric pressure.
![Page 3: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/3.jpg)
Electric Charge
• In 1909 Robert Millikan discovered charge was “quantized.”
• This means there is a smallest amount.• Thing about it like this, In order to have a
car all the pieces must be there. If you try to take the engine out, it’s no longer a car.
• Electric charge is much the same.• The electron has a set charge, take some
away and it’s no longer an electron.
![Page 4: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/4.jpg)
The Millikan Experiment
• Click here to recreate the Millikan oil-drop experiment
![Page 5: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/5.jpg)
Charged Particles
• Protons (+e): Mass = 1.673 x 10-27 kg, Charge = 1.60 x 10-19 C
• Neutron: Mass = 1.675 x 10-27 kg, Charge = 0
• Electron (-e): Mass = 9.11 x 10-31 kg, Charge = -1.60 x 10-19 C
e = 1.60 x 10-19 C
![Page 6: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/6.jpg)
Neutral Objects
• If the number of electrons equals the number of protons the object is said to be electrically neutral.
• In general q (charge) = Ne, where N is an integer.
• Since proton are much more difficult to remove, most objects are charged by removing or adding electrons.
![Page 7: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/7.jpg)
Charged Objects
• When two dissimilar materials are rubbed together electron usually go from one to the other.
• Look on the triboelectric scale to see which way they go, positive or negative
• Also, charge is conserved.
• The net charge of an isolated system is constant
![Page 8: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/8.jpg)
Like and Unlike charges
• Like charges repel each other
• Unlike (opposite) charges attract
![Page 9: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/9.jpg)
Conductors & Insulators
• Materials that have lose valence electrons are conductors
• Materials with tightly held valence electrons are insulators
• Can you think of some?
![Page 10: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/10.jpg)
Charging by Induction (Conductors)
Click on the picture to open an applet
![Page 11: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/11.jpg)
Polarization (Insulators)
![Page 12: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/12.jpg)
Coulomb’s Law
• F = 1/(4o) q1q2 / r2
– F = Force (N)
– o = 8.85 x 10-12 (electric permittivity of a vacuum)
– q = charge (Coulombs)– r = distance between charges
• 1/(4o) = k
![Page 13: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/13.jpg)
Point Charges
• When more than two charges are acting on each other we sum the forces.
• Treat each pair independently, then add the forces.
q1 q2 q3
r1 r2
![Page 14: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/14.jpg)
Point Charges in 2D
• When more than two charges are acting on each other in 2D, sum the forces for x and y dimensions.
• Again, treat each pair independently, then add the forces.
q1 q2
q3
r1r 2
![Page 15: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/15.jpg)
Electric Field
• Just like mass create gravitational fields, charges create electric fields
• With gravity the field strength is measure as Newton per kilogram
• What do you think Electric fields are measured in?
Newton's per Coulomb
![Page 16: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/16.jpg)
Measuring the Electric Field
• If the unit is Newton's per Coulomb, what is the equation?
E = F / qo
• Simple enough, right.
• E = Electric Field
• F = Force
• qo = charge producing field
![Page 17: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/17.jpg)
Summing electric Fields
• It is the surrounding charges that create an electric field at a given point in space.
• Look at Example 8
![Page 18: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/18.jpg)
Parallel Plate Capacitors
• To store charge a capacitor is used.
• The most common type is a parallel plate capacitor.
• Charge is spread uniformly, not really, through out the plate
• E = q /oA = / o
• = charge Density
![Page 19: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/19.jpg)
Picturing the Electric Field
Click on the picture to open an applet
![Page 20: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/20.jpg)
Electric Field Rules
• Fields start at positive and end at negative, or start or end at infinity.
• This is by convention. The field is said to predict the movement of a positive charge.
• The density of lines should represent the strength of the field.
• A positive charge will have a velocity tangent to a field line.
• Field lines do not actually exist since the are an infinite number of paths a test charge can take.
![Page 21: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/21.jpg)
Electric Fields Inside Conductors
• Excess electric charge moves to the surface of a conductor
• At equilibrium the electric field inside a conductor is zero– This comes from the fact that free
electrons will not move inside the conductor.
• So the electric field lines don’t penetrate the conductor
• The electric field outside a conductor is perpendicular to the surface
Click here for more info
![Page 22: Electric Forces & Fields Chapter 18. The Origins of Electricity In the mid 18 th century Ben Franklin created the idea on positive and negative electric](https://reader034.vdocuments.site/reader034/viewer/2022051819/55144f805503462d4e8b504f/html5/thumbnails/22.jpg)
Triboelectric Scale• Human hands (usually too
moist, though) (Very positive)• Rabbit Fur• Glass• Human hair• Nylon• Wool• Fur• Lead• Silk• Aluminum• Paper• Cotton• Steel (Neutral)
• Wood• Amber• Hard rubber• Nickel, Copper• Brass, Silver• Gold, Platinum• Polyester• Styrene (Styrofoam)• Saran Wrap• Polyurethane• Polyethylene (like Scotch
Tape)• Polypropylene• Vinyl (PVC)• Silicon• Teflon (Very negative )