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# Unit 8: Electrostatics

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## Brandon Branch

on 10 May 2018

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#### Transcript of Unit 8: Electrostatics

Electrostatics & Magnetism
Electrostatics
Electric Fields
E
-Fields Intro
Magnetic Fields & Moving Charges
Force felt by a charge moving thru a magnetic field.
Magnetic Fields
What is a Magnet? How does it work?
Coulomb's Law
Introduction
Ex 10 & 11
Ex 10. A student stores 3mC of charge by rubbing a blue balloon on their head, while another student stores 5uC of charge by rubbing a red balloon with wool. What is the force exerted on the blue balloon if the balloons are 0.15m apart?

Ex 11. Beryllium has an atomic number of 4, which means it has 4 protons in its nucleus. What is the force exerted on an electron that is 80pm from the nucleus? Is the force felt by the nucleus greater or less than the force felt by the electron? Explain
F=qvB
Ex. 31: A magnetic field enclosed a 4cm piece of wire and exerts a 3N force downward on the wire, as 2A of current passes through the wire from right to left. What is the magnitude and direction of the magnetic field?

Ex. 32 A 2m section of power lines is subject to a 4mT magnetic field from current passes through near by power line. What is the force felt by this 2m power line when 500A of current is passes through it?
Chapter 20, 21 & 24
The study of stationary electric charge.
Ex1. Copy the picture above and draw the distribution of charges as a negatively charged rod is brought near the electroscope.

Ex2. How would the leaves behave if a positively charged rod were used instead?

Ex. 3 Are electroscope made of insulating or conducting material? Explain
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Ex4. Copy the picture above and draw the distribution of charges as a positively charged rod is brought near and touches the electroscope.

Ex5. How would the leaves behave if a negatively charged rod were used instead?

Ex. 6 What would happen to the leaves of the electroscope in the 3rd picture if a negatively charged rod where brought near it? How about a neutral or positively charge rod?
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Ex 7: Why does the lion's Hair stand on end? What does that tell you about the lion's body?

Ex 8: How does a Balloon that holds a static charge stick to the the wall? How might humidity effect how long the balloon will stay attached to the wall?
Ex 9. What is the difference between charging by conduction and charging by induction? What type is the lion experiencing?
Ex. 12 & 13
Ex. 12 Two electrons are 2.3um apart, what is the force felt by each charge?

Ex.13 Three charges A,B, and C are all stationary in a row. Charge A is a 4uC charge is that is 2mm from C is a -3uC charge. If charge B is a 2uC charge that is 1mm from both A and C. What is the net force exerted on each charge?
1mm
1mm
Some calculations
Q
q
q
*If both q's are positive which q feels a greater force from the charge Q? Explain
E
-Field Diagrams
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Ex. 14 What is the charge on each charge below? Explain.
Ex 15. What is the charge on the blue charge and how does the magnitude of the blue charge compare to that of the red charge?
Ex. 16 Rank the locations (A,B,C,D) based on the force felt by a positive test charge, explain your reasoning.
A
B
C
D
Ex. 17 - What is the strength and direction of the electric field 1.0m to the left of a 3uC charge?
How does this change if the charge is negative instead?

Ex. 18 - A small test charge is placed 0.04m to the right of an electron. What is the magnitude and direction of the electric field at this location?

Ex. 19 When the electron from ex 18 is replaced with an unknown charge, the test charge is subject to a 0.0000018 N/C electric field, what is the charge of the unknown charge?
E-Field Examples
More E-Field Examples
Ex. 20 - Calculate the electric field strength 0.2m to the right of a 4uC charge. Which way does the field point at this location. What is the force felt by -2uC charge placed at this location.

Ex. 21 - A proton is placed 0.02m from an unknown charge. The proton feels a force 0.0003N towards the charge. What is the magnitude of the electric field at this location?

Ex. 22 - A -6uC charge is placed in a -400,000N/C electric field. What is the force felt by each charge? If the two charges are separated by 0.05m what is the magnitude of the charge that created the electric field?
E-Fields Cont'd
E-Field Eqn ex 15&16
Ex 25: Draw the magnetic field surrounding a horseshoe magnet.
Ex. 23: Below are microscopic pictures of the magnetic domains in a very thin film of magnetic material. Which domains do you think are magnetized? Explain.
Ex. 24: Rank the domains from greatest to least magnetization.
Ex. 26: Draw the magnetic field that surrounds the Earth, place an X where you believe the field is the strongest and an O where you think it is the weakest.
What causes the Northern Lights?
ex. 27 A proton is traveling left to right at 3x10^6 m/s, when it encounters a 2T magnetic field pointing towards you. What is the force felt by the proton? How would the force change if the charge where an electron instead?

ex. 28 An electron traveling away from you at 2 x 10^4m/s feels a 5x10^-8 N force, causing the electron to be pushed down. What is the magnitude and direction of the magnetic field.
Ex. 29. The picture below shows a magnetic field and an unknown charge with its velocity vector.
a. Use a solid line to draw the path the charge would take if it were positively charged.

b. Use a dashed line to draw the path the charge would take if it were negatively charged.
Ex. 30 the picture below shows the path of a unknown charge as it passes through a magnetic field with a speed of 1.25x10^5 m/s.
What is the charge on the unknown charge if the magnetic field is 0.75T, the circular path has a radius of 0.32mm and the charge feels a 3uN force.
F=ILB
N
S
Right Hand rule Practice
WHY MATERIALS ARE MAGNETIC
MAGNETIC FIELD LINES
Force surrounding a current carrying wire
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