Electricity and Magnetism Test Review. Static Electricity Def: Electricity created by a group of electrons staying together in one place. Electrons.

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.