Static Electricity

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Static Electricity

• Review

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2 Types of Charge

1. () charge----proton
2. (-) charge----electron

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Basic Law of Electrostatics

• Like charges repel
• Opposite charges attract

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Electroscope

• Used only to detect charge. Cannot tell type of
  charge.

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3 Ways to charge an object

1. Conduction--touching
2. Frictionrubbing together
3. Inductionrearrangement of charges on a neutral
   object, caused by a nearby charged object.

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Electric Field

• Area surrounding a charge where the affects of
  the charge can be felt.
• Strength depends on 2 things
• Size of the charge
• Distance from the charge

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Conductors vs. Insulators

• Conductorsallow electricity to flow through
  them.
• Metalscopper, zinc, aluminum, etc.
• Insulatorsdo not allow electricity to flow
  through them.
• Non-metalsPlastic, rubber, etc.

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The ability to charge an object is one thing, the
ability to move that charge is another.
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How do you Shock someone?
Think about all of the steps!!
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Compare Gravitational Potential Energy to the
flow of electricity
Will this ball roll down the hill without any
help? WHY?
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Will this ball roll without any help?
Why?
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Will this ball roll without any help?
Why?
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In order to roll, a ball must be moving from
high ground to low ground!
Ball must move from high potential to low
potential!!!
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Same with electricity.

• Differences in the number of electrons will cause
  them to move down the hill
• Charges move because of differences in the number
  of electrons.

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What will happen? Then what? Then what?
Until when? Then what???
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Electrons will continue to flow as long as there
is a difference in the number of electrons!!!
Potential Difference(V)also known as
Voltage
---difference in potential( of electrons)
between 2 places. ---Measured with
a Voltmeter ---Measured in Volts(V)
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How do we keep an electric potential between 2
points??
By keeping the number of electrons higher !! By
maintaining a potential difference!
How though?
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Well what do you do when your CD Player wont
work? Or when your IPod quits?
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You force there to be a potential difference!
Right on!!! You change the batteries, or you
charge it back up!!
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2 Types of batteries

1. Dry Cell Batterythey are dry
2. Wet Cell Batterythey are wet

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Dry Cell Battery
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Wet Cell Battery
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Current(I)

• Rate of flow of electrons
• How much electricity is flowing
• Measured in Amperes(A)

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Resistance(R)

• Tendency for a material to oppose the flow of
  electrons
• Typically, converting electric energy to thermal
  energy
• Measured in Ohms(W)
• The resistance of a material(a wire) depends on 2
  things
• Length
• Thickness
• Resistance controls the amount of current that
  flows through a circuit!!

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Ohms Law

• Current is directly proportional to the potential
  difference and is inversely proportional to the
  resistance.
• V I R

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What voltage is required to have a 3 A current
flowing through a 5 W resistor?
V I R V 3 A(5 W) V 15 V
Given I 3A R 5 W V ????
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Ex. A 9V battery is connected to a circuit. A
current of 2.5 A flows through the circuit. What
is the resistance of the circuit?
Given V 9V I 2.5A R ????
V I R
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Ex. A hairdryer with a resistance of 400 W is
connected to a common household outlet with 110 V
of potential difference. How much current flows
through the hairdryer?
Given R 400 W V 110 V I ????
V I R
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A 3 A current flows through a circuit that has a
resistance of 9 W. What voltage is required?

1. 3 V
2. .33 V
3. 12 V
4. 27 V

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A CD player draws 5 A of current when connected
to a 9 V battery. What is the resistance of the
CD player?

1. 45 W
2. 14 W
3. 1.8 W
4. .56 W

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A 1.5 V battery is required to maintain the
correct current through a 2 W circuit. What is
the current through the circuit?

• 3.5 A
• 3 A
• 1.33 A
• .75 A

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What determines whether electricity will or will
not flow?

1. Current
2. Potential Difference(Voltage)
3. Resistance

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What determines how much electricity will flow?

1. Current
2. Potential Difference(Voltage)
3. Resistance