Static Electricity Static Electricity rubs her feet on the carpet - PDF document

Static Electricity 1 Static Electricity 2 Introductory Question Introductory Question A woman rubs her feet on the carpet and gives A woman rubs her feet on the carpet and gives � a shock to her identical twin. If the twin also a shock to her identical twin. If the twin also Static Electricity Static Electricity rubs her feet on the carpet before being rubs her feet on the carpet before being touched, the shock will be touched, the shock will be touched the shock will be touched the shock will be larger larger A. A. smaller smaller B. B. the same size the same size C. C. Static Electricity 3 Static Electricity 4 Observations about Observations about 6 Questions about 6 Questions about Static Electricity Static Electricity Static Electricity Static Electricity � Static electricity builds up on Static electricity builds up on some objects some objects � Why do some clothes cling while others repel Why do some clothes cling while others repel? ? � Clothes in the dryer often develop static charge Clothes in the dryer often develop static charge � Why do clothes normally neither cling nor repel? Why do clothes normally neither cling nor repel? � � Objects with static charge may cling or repel Objects with static charge may cling or repel � Why does distance reduce static effects? Why does distance reduce static effects? � � Static electricity can Static electricity can cause shocks cause shocks � Why do clingy clothes stick to uncharged walls? Why do clingy clothes stick to uncharged walls? � Static electricity can make your hair stand up Static electricity can make your hair stand up � Why do clingy clothes crackle as they separate? Why do clingy clothes crackle as they separate? � � Why do some things lose their charge quickly? Why do some things lose their charge quickly? Static Electricity 5 Static Electricity 6 Question 1 Question 1 Electric Charge (Part 1) Electric Charge (Part 1) � Why do some clothes cling while others repel Why do some clothes cling while others repel? ? � Clothes that cling or repel carry a physical Clothes that cling or repel carry a physical � quantity called electric charge or simply “charge” quantity called electric charge or simply “charge” � Charge comes in two types: Charge comes in two types: � Charges of the same type repel Charges of the same type repel Ch Ch f h f h l l � Charges of different types attract Charges of different types attract � Franklin named the types “positive” and “negative” Franklin named the types “positive” and “negative” � Clothes acquire static charges while in the dryer Clothes acquire static charges while in the dryer � Clothes that cling evidently carry opposite charges Clothes that cling evidently carry opposite charges � Clothes that repel Clothes that repel evidently evidently carry like charges carry like charges 1

Static Electricity 7 Static Electricity 8 Question Question 2 2 Electric Charge Electric Charge (Part (Part 2) 2) � Electric charge Electric charge � Why do clothes normally neither cling nor repel? Why do clothes normally neither cling nor repel? � � is a conserved is a conserved quantity quantity � What happens in the dryer to cause static effects? What happens in the dryer to cause static effects? � is is quantized in multiples of the fundamental charge � Electric charge is measured in coulombs � Electric charge is measured in coulombs 19 coulombs � One fundamental charge is 1.6 × 10 -19 � Charge is intrinsic to some subatomic particles � Each proton has +1 fundamental charge � Each electron has –1 fundamental charge Static Electricity 9 Static Electricity 10 Net Charge Net Charge Charge Transfers Charge Transfers � An object’s net charge An object’s net charge � Contact can transfer Contact can transfer electrons between electrons between objects objects � is the sum of is the sum of all its all its individual charges individual charges � The object with the stronger The object with the stronger affinity for affinity for electrons electrons gains electrons and becomes gains electrons and becomes negatively negatively charged charged � tends tends to be zero or nearly to be zero or nearly zero zero � The other object loses electrons and becomes � The other object loses electrons and becomes The other object loses electrons and becomes The other object loses electrons and becomes � An electrically A An electrically neutral A l l i i ll ll neutral object l bj object bj positively charged positively charged � contains as many + charges as contains as many + charges as – – charges charges � Rubbing objects Rubbing objects together ensures together ensures � has zero has zero net net charge charge � excellent contact between their surfaces excellent contact between their surfaces � Clothes tend to be neutral Clothes tend to be neutral � � significant charge transfer from one to the other. significant charge transfer from one to the other. � Neutral clothes neither cling nor repel Neutral clothes neither cling nor repel � � A dryer charges clothes via these effects Static Electricity 11 Static Electricity 12 Introductory Question Introductory Question (revisited) Question 3 Question 3 (revisited) A woman rubs her feet on the carpet and gives A woman rubs her feet on the carpet and gives � Why does distance reduce static effects? Why does distance reduce static effects? � a shock to her identical twin. If the twin also a shock to her identical twin. If the twin also rubs her feet on the carpet before being rubs her feet on the carpet before being touched the shock will be touched, the shock will be touched, the shock will be touched the shock will be larger larger A. A. smaller smaller B. B. the same size the same size C. C. 2

Static Electricity 13 Static Electricity 14 Electric Charge Electric Charge (Part Question 4 Question 4 (Part 3) 3) � Two Two charges push charges push or pull or pull on one another on one another � Why do clingy clothes stick to uncharged walls? Why do clingy clothes stick to uncharged walls? � with forces that are with forces that are equal equal in magnitude in magnitude � but but opposite opposite in direction. in direction. � These electrostatic forces are These electrostatic forces are Th Th l l i f i f � proportional to the amount of each charge proportional to the amount of each charge � inversely proportional to (distance between charges) inversely proportional to (distance between charges) 2 � Electrostatic Electrostatic forces obey Coulomb’s law: forces obey Coulomb’s law: ⋅ ⋅ Coulomb constant charge charge 1 2 force = 2 (distance between charges) Static Electricity 15 Static Electricity 16 Electric Polarization Electric Polarization Question 5 Question 5 � A neutral A neutral wall contains countless charges wall contains countless charges � Why do clingy clothes crackle as they separate? Why do clingy clothes crackle as they separate? � � When When a negatively charged sock nears a negatively charged sock nears the the wall, wall, � � the wall’s positive charges shift toward the sock, the wall’s positive charges shift toward the sock, � the wall’s negative charges shift away from it, the wall’s negative charges shift away from it, h h ll’ ll’ i i h h hif hif f f i i � and the wall becomes electrically polarized. and the wall becomes electrically polarized. � Opposite charges are Opposite charges are nearer and nearer and attract strongly attract strongly � Like charges are farther and repel less strongly Like charges are farther and repel less strongly � The The charged sock clings to the polarized wall charged sock clings to the polarized wall Static Electricity 17 Static Electricity 18 Voltage Voltage Separating Opposite Charges Separating Opposite Charges � Charge has electrostatic potential Charge has electrostatic potential energy (EPE) energy (EPE) � Separating opposite charges takes work, Separating opposite charges takes work, � � Voltage measures the Voltage measures the EPE EPE per unit of charge per unit of charge � so the positive charges undergo a rise in voltage so the positive charges undergo a rise in voltage � and the negative charges undergo a drop in voltage. and the negative charges undergo a drop in voltage. � Raising the voltage of positive charge takes work Raising the voltage of positive charge takes work � Positive charge at high P P Positive charge at high voltage i i i i h h hi h hi h voltage l � Lowering the voltage of negative charge takes work L Lowering the voltage of negative charge takes work L i i h h l l f f i i h h k k k k � Voltage is measured in Voltage is measured in volts (joules/coulomb) volts (joules/coulomb) � can can release release EPE by EPE by moving to lower voltage moving to lower voltage � may move by may move by way of a discharge or spark! way of a discharge or spark! � Negative charge Negative charge at low voltage, at low voltage, � can release EPE can release EPE by moving to higher by moving to higher voltage voltage 3