electricity and magnetism test review. static electricity def: electricity created by a group of...
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Electricity and Magnetism
Test Review
Static Electricity
• Def: Electricity created by a group of electrons staying together in one place.
Electrons
Electric Charge
• How can an object collect electrons to get an electric charge?
Electric Charge
• How can an object collect electrons to get an electric charge?
• FRICTION!!
- - - - - - - -
Types of Electron Buckets
• What are buckets called where electrons stay put when they are placed inside?
Types of Electron Buckets
• What are buckets called where electrons stay put when they are placed inside?
INSULATORS:
Rubber
Plastic
Types of Electron Buckets
• What are buckets where electrons are free to move around in?
Types of Electron Buckets
• What are buckets where electrons are free to move around in?
CONDUCTORS:
Metal
Water
Types of Electron Buckets
• What is it called when a conductor is connected to the GROUND?
Types of Electron Buckets
• What is it called when a conductor is connected to the GROUND?
GROUNDING!
Multiple Charged Objects
• Imagine two objects, one with +10C of charge and the other one neutral.
+10CNo Charge
Multiple Charged Objects
• They are brought together and touch. Then are separated…
+10C No Charge
Multiple Charged Objects
• What charge does each object have now?
??? ???
Multiple Charged Objects
• The total initial charge was split between the two objects.
+5C +5C
Multiple Charged Objects
• Complete the practice problem on you review sheet.
??????
Total Charge
• Imagine two neutral objects. Then several electrons are sent form one to the other. What is the TOTAL charge of the WHOLE system?
1) 2)Electrons
Neutral Neutral - +
Total Charge
• TOTAL # of electrons and protons between both objects stays the same, so the TOTAL CHARGE on the SYSTEM stays the same. (Even though balloon is – and face is +)
1) 2)Electrons
Neutral Neutral - +
Charge Interaction
• Imagine a charged balloon and a pith ball…
Charge Interaction
• What happens to the pith ball if the balloon is NEGATIVELY charged?
-q
Charge Interaction
• The ball is attracted to the balloon
-q
Charge Interaction
• What happens to the pith ball if the balloon is POSITIVELY charged?
+q
Charge Interaction
• The ball is STILL attracted to the balloon
+q
Charge Interaction
• What happens if the pith ball AND the balloon are both NEGATIVELY charged?
-q -q
Charge Interaction
• The pith ball moves AWAY from the balloon.
-q -q
Electric Fields
• Consider the electric field map below.• Recall: WWPD
AB
Electric Fields
• What is the charge on A and the charge on B?
AB
Electric Fields
• What is the charge on A and the charge on B?
A +B -
Coulomb’s Law
• Coulomb’s Law gives the force between two charged objects.
• Be careful of units and scientific notation when working problems.
221
d
qqkF celec
Coulomb’s Law
• Coulomb’s Constant:
• q1 and q2: charge on two objects• d: distance between the two objects
2
291099.8C
Nmxkc
Coulomb’s Law• One hot air balloon flies through a thundercloud and comes
out with a charge of -1000C. Another balloon below has a positive charge of +900C of charge. If they are separated by a distance of 200m, what is the electrostatic force between the two balloons?
Coulomb’s Law
• Inverse square Law:
• What happens if you double, triple, etc the distance??
221
d
qqkF celec
Coulomb’s Law
• Inverse square Law:
• If distance is___________, F is _________.doubled ¼tripled 1/9quadrupled 1/16
221
d
qqkF celec
Current Electricity
• Current electricity involves electrons moving through conductors.
Current
• Def: How fast electrons flow past a fixed spot.
• Formula:
• Current is measured in Amps
t
QI
Voltage
• Def: The amount of Potential Energy in a circuit.
• Voltage is measured in Volts.
Power
• Def: The amount of electricity that is used by an object.
• Power is measured in Watts
Resistance
• Def: Measure of how much electrons are slowed down when they go through a resistor.
• Resistance is measured in Ohms (Ω)
The Formulas
IRV
IVPt
QI
(Ohm’s Law)
Q
I t
P
I V
V
I R
Power Bills
• To calculate a Power Bill, Power must be in kilowatts and time in hours.
• Bill= rate*kW*h
• Kilo: 1000 (1000 Watts in 1 Kilowatt)
Practice
• Complete the practice problems for a classwork grade.
Circuits
• Two main types of circuits
• Series Circuit- One lane road
• Parallel Circuit- Interstate
Ohm’s Law- WHOLE Circuit
• What is Rtotal for the circuit? What is the current?
5V
3 Ω
5 Ω
Ohm’s Law- EACH Resistor
• What is the voltage in each resistor?
5V
3 Ω
5 Ω
PARALLEL Circuits
• Which resistor has the greatest current flowing through it?
10V
2 Ω 4 Ω
Magnets and Magnetic Fields
• Magnetic Fields are SIMILAR to electric fields.• Consider the following magnet.
1 2
Magnets and Magnetic Fields
• Fact: Field Line ALWAYS leave the North Pole and enter the South Pole
1 2
Magnets and Magnetic Fields
• Which end is North and which is South?
1 2
Magnets and Magnetic Fields
• Which end is North and which is South?
N S
Magnetic Fields- Right Hand Rules
Use your right hand!!!!
Right Hand Rule #1
• What does a magnetic field, B, look like around a wire?
• Grab some wire with your RIGHT hand
I
Right Hand Rule #1
• Make sure your thumb is going in the same direction as the current is!
I
Right Hand Rule #1
• Your 4 fingers are lined up with the magnetic field. It goes in a circle around the wire.
I
Right Hand Rule #2• Right Hand Rule #2 tells us in what direction
the wire will be pushed…
N (+)
S (-)
B
I
Right Hand Rule #2• Step 1- Index finger of RIGHT hand points in
the direction of the current (I).
I
S
N
B
Right Hand Rule #2• Step 2- Point little finger in the direction of the
magnetic field B.
I
S
N
B
Right Hand Rule #2• Step 3- Stick your thumb out. Which way is it
pointing?
I
S
N
B
INTO the page!
Right Hand Rule #2• This is the direction of the force on the wire.
The wire will move INTO the page.
I
S
N
B
INTO the page!
Generators
• Right Hand Rule #2 can be used to generate electricity as well…
Generators
• Any device that transfers mechanical energy into electrical energy is called a generator.
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