Chapter 11 - Static Electricity

Day 1

• Introduction

• Sect 11.1

• Hw: Questions

• Electrostatics–The study of electric charge.–Charges cannot be created, they can

just move; this is how objects become charged.

• Static Electricity – is electricity that does not move, it

stays where the friction happened.

Objects can be charged or not charged.• POSITIVE – ______________• NEGATIVE – ______________• NEUTRAL – ______________

Draw in neutral, positive, and negative object with 8 total charges in the boxes below.

NEUTRAL POSITIVE NEGATIVE

+-+ -

Law of Electric Charges

• The Law of Electric Charges states that like charges repel and opposite charges attract.

+ +/-

+

+ +

-

• Neutral objects have no overall charge. Charged objects attract neutral objects.

Draw a diagram of a negatively charged object brought close to a neutral object.

=

NEUTRAL POSITIVELY CHARGED

+

=

NEUTRAL

Insulators and Conductors

• Insulators– are materials where the charge stays on the spot

where you rub the object. They do not let charges move freely (inhibit or prevent the movement of electrons).

Ex. Mostly non-metals, rubber (balloon)• Used as a safety precaution Ex… • Protect us from the danger of having large

amounts of electric charge move through our bodies if we come in contact with a conductor

Insulators and Conductors• Conductors

– are materials that do let charges move freely (allow the movement of electrons).

Ex. Most metals, copper, non-pure water (ions)• Pure water has NO IONS (ions = charged particles)

making them NON-CODUCTIVE• Tap, bottled, and salt water have IONS =

CONDUCTIVE

Why is it dangerous to touch an electrical appliance when your near water, wet, or in water (pool, puddle, or bath)?

Detecting Charge

• An electroscope is a device that can detect the presence of charge. Although they can come in many different shapes and sizes, they all achieve the same purpose.

– 2 Main Types

1.) Pith Ball Electroscope

• Consists of a ball of pith (plant material) suspended by a thread.

• Tests for the presence of a charge • The ball is neutral, if the object is charged the pith ball will be drawn towards it.

2.) Metal Leaf Electroscope

• There are two lightweight strips of metal that bend easily.

• These “leaves” are attached to a central metal rod with a metal sphere at the top.

• Since the sphere, rod, and leaves are all metal (conductors) electrons can move freely within them.

• When the metal leaves become charged (positively or negatively) they become charged the same and therefore repel each other. – The metal leaves moving away from each other is proof

they are both charged• Pg. 471 Q: 3-9

Day 2• Sect 11.2 - Pg. 482• PPT: Charging by CONDUCTION• Bell Work (have HW questions out) How might technology be enhanced with the use of electricity? How might technology be improved with our new knowledge of the law of electric charge?How might yesterdays lesson prove helpful in the future?

Review• Static electricity

– Stationary (no free flow of electrons) • Law of electric charge

– Opposites attract, same charge repel • Insulators vs. conductors

– One allows movement one prevents• Electroscope

– Two types• Pith ball & metal leaf

HW• Pg. 471 Q: 3-9

3. a) Which particles are difficult to add or remove from an atom? • Protons and neutronsb) Which are easier to add or remove• Electronsc) How does a/b explain the formation of + and – charged objects?• Illustrates that electrons can move (leave their atom)

and move into another, creating a imbalance of charges (- if added, + if removed)

HW4. Describe the total charge on each of the following objects as either neutral, positive, and negatively charged• 13- the object is neutral – balance of charges• 14 – Negative because more – than + 5. What would you do to the object in fig 15 to make it neutral? • Add 2 negative charges to balance it 6. What would you do to make it + charged? – charged?• Remove electrons = +, add electrons = -

HW7.Would the following repel or attract? a) + beside a –• Opposites attract a) - beside a – • Like charges repel 8. a) how does a electrostatic pain sprayer work? • Paint = +, surface = -… attraction ensures

coverageb) Are they beneficial? • Yes. Reduce amount of misses spots/paint used

Charging by Conduction• Neutral objects can become charged through

conduction in two different ways – charging by friction (1) and charging by contact (2).

1. Charging by Friction• When you rub two different neutral objects

together, they become charged.• One material is more likely to gain electrons

becoming negatively charged.• The other material is likely to give up electrons

becoming positively charged.

How does the air effect an objects charge? • Humid air has more water, collisions btw water

and nearby charged objects cause a transferring of electrons and a reduction of charge.

How would one determine which of the neutral objects will become positively charged and which one will become negatively charged?

• Use the Electrostatic Series which is a list of materials in order from those with a weak attraction for electrons to those with a strong attraction for electrons.

• Pg. 473

Electrostatic Series

• Air• Human hands/skin• Rabbit fur • Nylon / Wool• Human Hair / Cat’s Fur• calcium, magnesium, lead• silk• aluminum, zinc• Cotton• Amber• Acetate / Rayon• Polyester• Cellophane tape • Saran• Vinyl / Teflon• Silicon Rubber

Weak hold on electrons-

Tendency to lose electrons

Strong hold on electrons-

Tendency to gain electrons

How to Use the Electrostatic Series• You can use the list to determine the charges that will

appear when two objects are rubbed together. Remember these rules!

1. Objects high on the list LOSE ELECTRONS easily, therefore, they develop POSITIVE charge after being rubbed.

2. Objects low on the list GAIN ELECTRONS easily, therefore, they develop a NEGATIVE charge after being rubbed.

3. When determining charges of rubbed objects, locate them on the list. The one higher on the list will be POSITIVE and the one lower on the list will be NEGATIVE.

Charging by Conduction (Friction)

• As we have learned, objects can be charged by friction. (REVIEW)

• When two neutral objects are rubbed together, one becomes positively charged and the other becomes negatively charged.

• The electrostatic series allows you to predict the charge of each object.

Charging by Conduction (2. Contact)

• Objects can also be charged by contact. • When a charged object touches a neutral object

the neutral object gets the same charge. • This occurs because the electrons move from one

object to the other

+ +

+

+

+ +

+ +

+ ++

++

--

--

-

---

-

--

--- -

- -

electrons

negatively charged

-

Draw a picture of a neutral pith ball being charged by contact by a positively charged object.

• If two charged objects come in contact, the electrons will move along a CONCENTRATION GRADIENT – from an area of high concentration (Neg.) to an area of lower concentration (Pos.)– Produces a more EVEN distribution of electric charge

btw the two objects.

Grounding

• removing excess charge (either positive or negative)

• involves transferring electrons between the object and a large neutral object such as Earth (the ground)– “infinite reservoir of electrons” = charge is spread

out and neutralized

The Symbol for Grounding =

HW: Pg. 477 #1,2,5,6

Day 3: Lab• Review Yesterday & Take up HW • HANDOUT: Lab – Charging by Conduction• Key Terms

– Grounding• Removing excess charges via the ground

– Electrostatic Series• List of materials based on likeliness of giving/taking electrons

– Conduction • Charging something involving touch - 2 types • Friction – rubbing two different materials• contact – a charged object touching another object

HW: Pg. 477 #1,2,5,6 1. predict the following pairs = Positive

– Glass and silk– Ebonite and fur– Human hair and rubber balloon– Amber and cotton

2. Why do objects made from different materials develop an electric charge when rubbed? What is this method called?

– Friction – one gives up ELECTRONS, the other takes them (based on electrostatic series)

HW: Pg. 477 #1,2,5,6

5. Two rods, X (+8) and Y (-4) touch…a) What particles moved?

– electrons

b) What rod did the particles move from? – Y – only electrons move…. Concentration gradient –

area of high concentration to an area of low, with respect to the excess of ELECTRONS

6. Describe how electrons travel when a positively charged object is grounded.

– Electrons would be PROVIDED by the earth (infinite reservoir), and supplied to the charged object until it became neutral

Day 4 :

• Review

• PPT Note: Charging by INDUCTION

REVIEW: Charging by CONDUCTION1: Friction - Rub

• two different neutral objects rub together to create friction

• one material readily gives up electrons to become positively charged while the other takes electrons to become negatively charged *(refer to electrostatic series)

• materials oppositely charged will attract according to the Law of Electric Charge

2: Contact - Touch• an already charged material

contacts a neutral one• electrons flow into or out of

the neutral material depending on the type of charge present in the charged material

• the neutral object will become charged identically to the charged object and they will immediately repel each other

CHARGING BY “INDUCTION”Sect. 11.6

Since we now know what charging by “CONDUCTION” means… what do you think “INDUCTION” refers to?

Charging by Induction 11.6

• Charging by induction indicates that there is an approach of an object but no contact.

• There are two forms of Charging by Induction…

A. TemporaryB. Permanent

A) Temporary charge by induction

• occurs when a charged object approaches a neutral one.

• When they are very close, electrons of the neutral material move within the object which sets up a polarity.

• Also called “induced charge separation” or ICS

Induced Charge Separation (ICS) • The electrons in the neutral object move to one end or the

other (depending on whether the charged object is + or -) in order to create attraction.

• Once the charged object is removed, the electrons in the neutral object return to their original state.

Neutral Pith Ball & Neg. Rod

+ + + + + -

-

- -

- - -

+ + + +

+ + + +

+ + + + +

-

-

-

-

Neutral Pith Ball & Pos. Rod

-

- -

-

-

-- -

-

-

-

-

+

+

++

+ +

++

+

+

++

Electrons in electroscope move down

leaves become –ve and repel

leaves become +ve and repel

Electrons in electroscope move up

Charging by Induction

A) Temporary charge by induction

• The neutral object becomes temporarily charged positive at one end and negative at the other (ICS).

• Since the induced charge is opposite the charge of the charged object, the two objects will attract.

*Once the original charged object is taken away, the electrons in the neutral object return to their normal arrangement.

B) Permanent charge by induction • Can happen via a ground wire. • During the approach of the charged object, a

ground wire is touched to the neutral material (to whatever side the electrons will shift to).

• The wire allows excess electrons to escape or supply additional electrons according to the type of charge on the charged object.

+ ++ +

+ + + + +-

-

--

-

-

-

-

+ ++ +

+ + + + +- -

--

-

--

-

-

--

-

---

-

“Induced Charge Separation”

4 Stages

This sets up 2 attractions: 1 - btw the pith ball and the negative rod2 – btw the ground and the and pith ball via the grounding wire…

The electrons from the rod cant jump (not strong enough) but what about the pith balls electrons?

“Induced Charge Separation”

4 Stages

This sets up 2 attractions: 1 - btw the pith ball and the negative rod2 – btw the ground and the and pith ball via the grounding wire…

The electrons from the rod cant jump (not strong enough) but what about the pith balls electrons?

B) Permanent charge by induction

• After the ground wire is used, the charged material is removed.

• In this method of charging, the induced charge will always be the opposite of the original charged material.

• In order for the charge to be permanent, the ground wire must be disconnected or removed before the charged object is removed.

HW

• 477 #1-3, 5, 6

• 489 #2, 5

Review

• On a blank page “Compare and Contrast charging by INDUCTION vs. CONDUCTION”– Treat this as a test scenario – Write down what you know without your notes

• Use your notes afterwards to fill in any missing important info

– Exchange with a peer• Correct spelling, grammar, and any missing info

CHARGING REVIEWConduction VS.

Via contact1. FRICTION• Rubbing two diff. neutral

objects– Relies on electrostatic

series

2. CONTACT• One charged one neutral

– Neutral object will obtain the same charge (electrons move down concentration gradient)

InductionWithout contact

1. TEMPORARY• Induced charge separation• Charged object approaches neutral

object, a temporary polarity (north vs. south pole) sets up

2. PERMANENT • Induced charge separation with a

grounding wire• Grounding wire provides electrons (if

charged object is positive) or removes them (if charged object is negative)– Cutting the grounding wire maintains the

temporary charge created

HW

• Take up any questions/concerns with HW from any student that completed the assigned HW

11.8 - ELECTRIC DISCHARGE(pg. 492)

11.8 - Electric Discharge (pg. 492)

• Def. Electric Discharge – Rapid transfer of excess charge btw two objects

• When two objects that have a charge imbalance (concentration gradient) are near each other or come in contact, electrons travel down the concentration gradient (from an area of high electron conc. to an area of low electron conc.)

• Can be visible as sparks• Greater the imbalance,

greater/more noticeable the discharge

• Discharges superheat the air around them, potentially causing burns or damaging electronic equipment

Think/Pair/Share – 3 min

• Lightning – How is lighting created or how does it work?

• Lightning Rods – How do they work? Why do we need them?

Lightning I. As water molecules move past each other they become charged

– Falling drops pick up electrons lower half the cloud negative, upper positive

II. Excess negative charge in the lower cloud repels the electrons in the earths surface creating a…?

• Induced Charge Separation (ICS)

++

+

++

+ ++ +

+++

++

5. electrons collide with air creating

heat & light

3. negative charges in

clouds repel negative

charges on the earth

earth surface (induction) =

positively charged

Lightning

4. negative charges jump from the cloud to the earth

1. particles in clouds rub together

causing charged particles

2. negative charges collect at the bottom of the

cloud

+ + ++ +++ + +

+++

+++

Lightning III. This creates a charge imbalance or a…?

IV. Once the imbalance is great enough, a discharge btw the cloud and the ground occurs

– Or btw clouds, or from earth to cloud

• “concentration gradient”

What is happening here?

Lightning Rods • Lightning travels along the path of least resistance

(easiest path electrons can find) • Lightning rods are composed of highly conductive

metals (iron or copper) that goes from a high object (top of house or barn) and reroutes it to the earth (grounding)

ICS

++

+

lightning bolt strikes rod

charges travel from the rod, through the wire and into the ground

Lightning Rods+

+

+ +

++

++

+

+

Chapter Review

Chapter 11 Review• Pg. 498 - Q 1, 2, 3, 6, 7, 10, 11, 15, 16, 18, 22,

23, 28, 29, 31

Self quiz• Pg. 500 – Q 1-23