electric charge

February 02, 2021

Return toTable ofContents

Electric Charge

Dem

o

https://njctl.org/video/?v=sD4cNtPC3jc

February 02, 2021

Charging by Rubbing

When you take two non metallic objects, such as a plastic rulerand animal fur and rub them together, you get an interestingeffect. Before they are rubbed, the plastic ruler is held over bitsof paper and nothing happens.

After the rubbing, the plastic ruler is held over the bits of paperand they are accelerated towards the ruler.

withoutrubbing

afterrubbing

...rub

February 02, 2021

Electric Charge

Since the paper bits were accelerated upwards, against theforce of gravity, what interaction was occurring between theruler and the paper? A Force.

It has been known since ancient times that when certainmaterials are rubbed together, they develop an attraction foreach other (This can be seen today when you take clothesout of a dryer).

In ancient Greece - people noticed that when thread wasspun over a spindle of amber, the thread was attracted to thespindle.

The Greek word for amber was "elektron," hence thisFORCE was called electric.

February 02, 2021

Electric Charge

Further experimentation showed that dissimilar materialswould attract each other after rubbing, while similar materialswould repel each other.

These effects would not happen without the contact, andlater, given enough time, the forces of attraction andrepulsion would stop.

This led to the thought that something was being exchangedbetween the materials - and this something was later named"charge." Because objects would be repelled or attracted, itwas postulated that this charge came in two types.

February 02, 2021

Electric Charge

In the 18th century, Benjamin Franklin named the two types ofcharge when he observed the attraction between a rubber rodand animal fur when they were rubbed together. Benjaminnamed the charge on the rod, negative, and the charge on thefur, positive.

When a glass rod is rubbed by silk, the rod acquires a positivecharge and the silk obtains a negative charge. The two rubberrods now repel each other, and a rubber rod is attracted to aglass rod.

February 02, 2021

Electric Charge

No new charge is created - instead, it is just separated - thepositive charge acquired by one object is exactly equal inmagnitude and opposite in sign to the charge lost by the otherobject.

What is another way of saying this?

February 02, 2021

Electric Charge

Electric Charge is a conserved quantity.

The total amount of electric charge in a closed system remainsconstant - it is neither created or destroyed.

Just like energy, linear momentum, and angular momentum areconserved quantities.

February 02, 2021

1 A neutral plastic rod is rubbed by a piece of animal fur.During the process, the plastic rod acquires a positivecharge and the fur:

A acquires an equal positive charge.

B acquires an equal negative charge.

C acquires a smaller positive charge.

D acquires a smaller negative charge.

EI need help

An

swer

https://njctl.org/video/?v=TmO1lDGBO_c

February 02, 2021

2 A positively charged object is moved towards anegatively charged object. What is the motion of theobjects when they come close to each other?

A Neither object has any affect on the other.

B The objects move towards each other.

C The objects move away from each other.

D The objects move towards each other, then moveaway from each other as they get closer (but theydon't touch).

EI need help

An

swer

https://njctl.org/video/?v=Gg4QykFPKGk

February 02, 2021

3 A neutral glass rod is rubbed by a piece of silk withno net charge. The rod gains a positive net chargeand the silk gains a net negative charge. What isthe sum of the charges on the silk and the rod?

A Zero.

B Twice the charge on the rod.

C Twice the charge on the silk.

D One half of the charge on the rod.

E I need help

An

swer

https://njctl.org/video/?v=tQS4VjLWrkU

February 02, 2021

4 Two pith spheres covered with conducting paint arehanging from two insulating threads. When the spheresare brought close to each other, they attract each other.What type of charge is on the spheres? After they touch,will they separate or cling together? Discuss allpossibilities.

An

swer

https://njctl.org/video/?v=dtVR5c6RCIE

February 02, 2021

February 02, 2021


Atomic Structure andSource of Charge

https://njctl.org/video/?v=TBsCcM1t6Dw

February 02, 2021

Atomic Structure

To understand where the phenomenon of electric charge comesfrom, the basic structure of matter needs to be discussed.

All matter is made up of atoms, which are made up of protons,neutrons and electrons.

Each atom contain a central nucleus that is composed of protonsand neutrons (nucleons). Electrons move around the nucleus inthe empty space of the atom.

Electrons are fundamental particles - they have no underlyingstructure. Protons and neutrons are not fundamental particles.They are made up of quarks - which are fundamental particles.

February 02, 2021

The Electron

J.J.Thomson found a particle that had a very low mass for itscharge. In fact, its mass per charge was 1800 times less than theprevious lowest amount measured for a particle. Before this work,physicists were speculating that the Hydrogen atom was thesmallest fundamental particle.

This led Thomson to propose that this negatively charged particlewas new - and he called them "corpuscles." The name "electron"was taken from George Johnstone Stoney's work in 1874, andproposed again by George F. Fitzgerald - and the name stuck.

Furthermore, since the electron was so much lighter than thehydrogen atom, it was concluded that it must be part of the atom.

February 02, 2021

Measurement of Charge

The electron was discovered by J.J. Thomson in 1897, and in aseries of experiments between 1909 and 1913, Robert Millikanand his graduate student, Harvey Fletcher, established the valueof the charge, "e," on an electron.

J.J. Thomson RobertMillikan

February 02, 2021

Measurement of Charge

Millikan and Fletcher's work and subsequent experiments haveestablished the value of "e" as 1.602 x 10-19 Coulombs.

It has also been demonstrated that this is the smallest value ofcharge (with the exception of quarks which will be coveredshortly) and all larger charges are an integral multiple of thisnumber.

Because small amounts of charge can generate large amountsof force, charge is often measured in:

milli-Coulombs (mC) = 10-3 C

micro-Coulombs (μC) = 10-6 C

nano-Coulombs (nC) = 10-9 C

February 02, 2021

Properties of the Electron

Further research showed that the electron has a mass of9.1 x 10-31 kg.

qe = e = 1.6 x 10-19 C

me = 9.1 x 10-31 kg

While finding the charge on an electron, it was discovered that thecharge on any object was an integral multiple of the electron charge.

Thus, you can have a charge of 3.2 x 10-19 C on an object, but youcan't have a charge of 3.0 x 10-19 C!

The charge on any object is always an integral (1, 2, ...,1,000,056, ...) multiple of 1.6 x 10-19 C.

February 02, 2021

5 Which of these choices could be the total charge on anobject (e = 1.6 x 10-19 C)?

A 0.80 x 10-19 C

B 2.0 x 10-19 C

C 3.2 x 10-19 C

D All of the above.

EI need help

An

swer

https://njctl.org/video/?v=EeWtEqDySgo

February 02, 2021

6 Which of these choices could be the total charge on anobject (e = 1.6 x 10-19 C)?

A 4.8 C

B 3.0 C

C 3.0 mC

D All of the above.

EI need help

An

swer

https://njctl.org/video/?v=sBXr2cDy_9k

February 02, 2021

7 The electron was discovered by:

A J. J. Thomson

B Robert Millikan

C Harvey Fletcher

D Ernest Rutherford

EI need help

An

swer

https://njctl.org/video/?v=3bh7W4j2Pwk

February 02, 2021

8 The electron charge was first measured accurately by:

A J. J. Thomson

B Robert Millikan and Harvey Fletcher

C Niels Bohr and Paul Dirac

D Ernest Rutherford

An

swer

EI need help

https://njctl.org/video/?v=FgSHu6PBC3A

February 02, 2021

February 02, 2021

Charge on Nucleons

Protons and electrons have equal and opposite charge. Byconvention (set by Ben Franklin), electrons have a negativecharge and protons have a positive charge. This is the originof charges on material objects. Neutrons have no charge(neutral).

Atoms are electrically neutral - not because they contain nocharge - but because they have equal numbers of protonsand electrons - their total charge adds up to zero.

If an atom gains electrons, it has a net negative charge and iscalled a negative ion. If it loses electrons, then it has apositive charge and is called a positive ion.

https://njctl.org/video/?v=Xtemx_8tIhA

February 02, 2021

The Nature of Charge

Like energy and momentum, charge is neither created nordestroyed, it is conserved.

Opposite charges attract and like charges repel. As a resultnegatively charged electrons are attracted to the positivenucleus.

Despite the great mass difference, the charge on an electronis exactly equal in magnitude to the charge on a proton, andits magnitude is denoted by "e."

An electron is has a charge of -e anda proton, a charge of +e.

February 02, 2021

What the atom doesn't look like:

This is NOT what an atom looks like!!!

If an atom was magnified sothat the nucleus was the size ofa baseball, the atom wouldhave a radius of 4 km.

And the electrons would beapproximately the size of theperiod at the end of thissentence. Atoms arealmost all empty space.

Since everything (including us) is made of atoms, that meanseverything (including us) is mostly empty space.

February 02, 2021

What the atom does look like:Here's a more realistic visualizationof a Helium atom. The nucleus isburied deep within the atom and is1,000,000 times smaller than theatom.

The two protons and two neutronsare shown in red and purple - thewidth of the nucleus is 1x10-7 nm.

The diagram shows a magnifiedview of the nucleus - it fits within thedarker circle.

What is the significance of the darkcircle surrounded by the lightershades of gray and pink?

http://commons.wikimedia.org/wiki/File:Helium_atom_QM_rev1.svg

February 02, 2021

What the atom does look like:You know that Helium has twoelectrons - yet they're not shownon this picture.

That's because we don't knowexactly where those electronsare. We only know a probabilityof where they are.

The darker the shade meansthat it is more probable that theelectrons are found within thatshape.

For more information, refer tothe Quantum Physics andAtomic Modeling chapter of theAP 2 Physics class.


February 02, 2021

What the atom does look like:


It has been shown that electriccharges move between objects.Based on this picture of theatom, which of the constituentsof the atom look like they couldmove?

Would it be the neutrons andprotons buried deep within theatom or the electrons?

February 02, 2021

What the atom does look like:


The electrons are the particlesthat will move between atoms -they are not bound together astightly as the protons and theneutrons.

The electrons are fundamentalparticles. At the moment,physicists have not found anyfurther structure within theelectron.

However - the same cannot besaid for the neutrons and theprotons.

February 02, 2021

Neutron and Proton Structure - Quarks!

By Javierha (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

http://commons.wikimedia.org/wiki/File%3ANeutr%C3%B3n-

Estructura_de_Quarks.png

Neutron

Neutrons and protons are actuallymade up of elementary particles calledquarks. Murray Gell-Man, along withGeorge Zweig, proposed theexistence of these particles to helpexplain the many different types ofparticles that make up matter.

Murray coined the term by taking itfrom James Joyce's novel, Finnegan'sWake, an interesting intersection ofphysics and art.

February 02, 2021





Neutron

There are six types, or flavors, ofquarks that describe their properties,and they are further classifiedaccording to their color (not a real color- just a handy inventory managementtool). They are: up, down, strange,charm, top and bottom.

And they have charges that are either±2/3 e or ±1/3 e! Before this work inthe 1960's, it was thought that thesmallest charge on a particle was e.

A neutron (to the left) is composed ofan up quark and two down quarks.

February 02, 2021





Neutron

The study of Quarks is called QuantumChromodynamics and is way beyondthis course.

But one final interesting point - thequark is subject to all four fundamentalforces - electricity and magnetism,gravity, strong nuclear, and the weaknuclear.

February 02, 2021

9 Which of the following are fundamental particles?Select two answers.

A Electrons

B Protons

C Neutrons

D Quarks

E I need help

An

swer

https://njctl.org/video/?v=5x70tHMlJk8

February 02, 2021

10 An atom in its normal (non-ionic) state has nocharge. This is due to the fact that atoms:

A have only neutrons.

B have no protons or electrons.

C have equal numbers of protons and electrons.

D have an equal number of protons and neutrons.

E I need help

An

swer

https://njctl.org/video/?v=N3gAddYkJPI

February 02, 2021

11 What object moves freely within the entire atom?

A Electron.B Neutron.C Proton.D Nucleus.E I need help

An

swer

https://njctl.org/video/?v=Ow0eXYojTWk

February 02, 2021

12 An atom is composed of:

A a central nucleus surrounded by electrons

B an even distribution of electrons and protons ina spherical shape.

C a central nucleus surrounded by neutrons.

D a central nucleus containing protons and electrons.

E I need help

An

swer

https://njctl.org/video/?v=dNlGTUtkDQA

February 02, 2021

13 What are neutrons and protons composed of?

A Nothing - they are fundamental particles.

B Corpuscles

C Electrons

D Quarks

EI need help

An

swer

https://njctl.org/video/?v=iqZWWFrOsxE

February 02, 2021

February 02, 2021

SolidsSolids are a form of matter whose atoms form a fixed structure.Nuclei, with their protons and neutrons, are "locked" intoposition.

Solids are classified as either conductors, insulators orsemiconductors.

In conductors, some electrons are free to move through thesolid and are not bound to any specific atom.

Electrons are bound to their atoms in insulators, and maymove short distances, but much less than the electrons in aconductor.

Semiconductors, depending on their situation, act as eitherconductors or insulators.

https://njctl.org/video/?v=bVKA-4FaJNw

February 02, 2021

In conductors, some electrons are mobile and can move freelyinside and on the surface of the solid.

Conductors

February 02, 2021

Insulators are materials that have strongly bound electrons thatcan move only short distances within the solid. Differentinsulators have varying levels of insulation capabilities.

Insulators

https://en.wikipedia.org/wiki/Insulator_(electricity)

February 02, 2021

14 Excess charge on a conductor will reside:

A on the surface of the conductor.

B at the center of the conductor.

C throughout the inside of the conductor.

D at the center and on the surface of the conductor.

EI need help

An

swer

https://njctl.org/video/?v=hvNRooVDe6g

February 02, 2021

15 Compared to insulators, metals are better conductors ofelectricity because metals contain more free _____.

A positive ions.B negative ions.C protons.D electrons.E I need help

An

swer

https://njctl.org/video/?v=rvRCZTGC8Qw

February 02, 2021

16 Electrons in an insulator are:

A bound to their atoms, but may move freelythroughout the solid.

B not bound to their atoms and may move freelythroughout the solid.

C bound to their atoms and may not move atall within the solid.

D bound to their atoms, but may moveshort distances within the solid.

E I need help

An

swer

https://njctl.org/video/?v=uiu78DSRTDU

February 02, 2021

17 Excess charge in an insulator will reside: Select twoanswers.

Awithin the insulator.

Bmidway between the center and the surface ofthe insulator.

Conly at the exact center of the insulator.

Don the surface of the insulator.

EI need help

An

swer

https://njctl.org/video/?v=-hfJXzs5Qgk

February 02, 2021

February 02, 2021


Conduction andInduction

https://njctl.org/video/?v=mZ4zdYpczNg

February 02, 2021

The Ground

Before a discussion of conduction and induction can takeplace, the concept of "the ground" needs to be understood.

Electrons can flow between objects - both conductors andinsulators.

Electrons can also flow from Earth, which is an excellentconductor, to the objects, and from the objects to Earth.Because of its massive size, the Earth serves as the ultimatesource and destination for electrons.

The concept of grounding will be discussed further in theElectric Potential unit of this course.

February 02, 2021

Grounding

When a wire is attached between the earth and a negativelycharged conductor, excess electrons flow to the earth leaving theconductor neutral. This is "grounding." A positively chargedobject will cause electrons to flow to it from the ground.

When you touch an object with a net negative charge, you mayget a shock. This is because the conductor wants to get rid of itsexcess electrons. To do this, electrons flow through you to theground. If the conductor had an excess positive charge, theelectrons would flow from the earth to you. In either case - thereis a spark!

Note: grounding used to be called "earthing," because ofthe flow of electrons to and from the Earth.

February 02, 2021

(symbol for "ground")

Grounding

Electrical circuits and devices areusually grounded to protect themfrom accumulating a net charge thatcould shock you.

To ground an electrical device, aconductor must run from the deviceinto the ground.

Plugs for many electrical deviceshave a third grounding pin thatconnects to a wire in the outlet boxwhich goes to the ground.

Dem

o

February 02, 2021

18 A positively charged sphere is touched with a groundingwire. What is the charge on the sphere after the groundwire is removed?

A Depends on the magnitude of the sphere's charge.

B Neutral.

C Positive.

D Negative.

EI need help

An

swer

https://njctl.org/video/?v=UqMZgpc7_20

February 02, 2021

19 A negatively charged sphere is touched with a groundingwire. What is the charge on the sphere after the groundwire is removed?

A Depends on the magnitude of the sphere's charge.

B Neutral.

C Positive.

D Negative.

EI need help

An

swer

https://njctl.org/video/?v=8oXVtHsj3BA

February 02, 2021

February 02, 2021

++

++

--

- -

-

-- -

Insulator

Charging by Conduction

Negatively Charged(charge = -4Q)

++

++- -

-

-

Insulator

Neutral Charge(charge = 0)

(identical spheres very far apart)

Charging by conductioninvolves conductors thatare insulated from theground, touching andtransferring the chargebetween them. Theinsulator is necessary toprevent electrons fromleaving or entering thespheres from the Earth.

Total Charge = -4Q

https://njctl.org/video/?v=1u9-ZHYrOpc

February 02, 2021

++

++

-

--

-

-

- ++

++

-

-

-

-

-

-

Insulator Insulator


Total Charge = -4Q

If the spheres are broughttogether to touch, theirelectrons push as far apartas they can, and the totalcharge is distributed equallybetween the two spheres. Notethat the total charge stays thesame.

(remember, similar charges repel)

February 02, 2021

++

++-

-

- -

-

-

Insulator

Charging by ConductionNegatively Charged

(charge = -2Q)

++

++

-

-

-

-

-

-

Insulator

Negatively Charged(charge = -2Q)

(very far apart)

Once they are moved apart again, the charges cannotget back to where they came from, as air serves as anexcellent insulator.

This results in an equal distribution of charge.

Total Charge = -4Q Dem

o

February 02, 2021

20 If a conductor carrying a net charge of 8Q is brought intocontact with an identical conductor with no net charge,what will be the charge on each conductor after they areseparated?

A-8 Q

B0 Q

C4 Q

D8 Q

EI need help

An

swer

https://njctl.org/video/?v=WiigMvnjbiw

February 02, 2021

21 Metal sphere A has a charge of -2Q and an identicalmetal sphere B has a charge of -4Q. If they are broughtinto contact with each other and then separated, what isthe final charge on sphere B?

A-2 Q

B-3 Q

C-4 Q

D-6 Q

EI need help

An

swer

https://njctl.org/video/?v=PQ6Ptrls82U

February 02, 2021

February 02, 2021

Charging by Induction

Charging by induction involves transferringcharge between two objects without themtouching.

++

++- -

-

-

InsulatorThis is a neutral conducting sphere,conducted to the ground via a wire.

https://njctl.org/video/?v=LoAKghAsM-Q

February 02, 2021


A negatively charged rod is broughtnear, but does not touch the sphere.Electrons within the sphere are repelledby the rod, and pass through the wire tothe ground, leaving a net positive chargeon the sphere.

+

-- - -

+

+

+-

---

++

++

Insulator The electrons are being pushed downthis wire into the ground.

February 02, 2021


While the negatively charged rodremains near the sphere, the ground isremoved. Note that there can be nomore movement of electrons since thesphere is isolated from the ground.Electrons cannot jump the gap betweenthe rod and the sphere or between theground and the sphere.

+

-- - -

+

+

+-

---

++

++

Insulator

The wire is removed, disconnecting thesphere from the ground.

February 02, 2021

Charging by Induction+

-- - -

+

+

+-

---

++

++

Insulator

The rod is then removed. It is importantto note that the charge on the rodremains constant (negative). The chargeon the sphere is now positive as it lostelectrons to Earth.

February 02, 2021

Conduction Summary

Through physical contact, a charged object will transfer aportion of its charge to a neutral object. Because of theConservation of Charge, the amount of charge on the initiallycharged object will decrease.

For example, a positively charged object will transfer positivecharge to a neutral object, leaving it with a net positive charge.The amount of positive charge on the initial object will decrease.

Similarly, a negatively charged object will transfer negativecharge to a neutral object.

February 02, 2021

Induction Summary

A charged rod will be brought close to a neutral, grounded object,but it will not touch it.

A positively charged rod will attract electrons from the ground tothe neutral object. A negatively charged rod will repel electronsto the ground. The ground is then removed.

The neutral object will be left with a charge opposite to thecharged rod.

February 02, 2021

Induction Summary

The rod will not lose any charge - the extra charge on theoriginally neutral object comes from the ground. As long as theground is disconnected before the initial object is removed, theneutral object will gain charge.

If the ground were left in place, once the charged rod is removed,the neutral object will pass its gained charge back to the ground.

February 02, 2021

22 Sphere A carries a net positive charge, and sphereB is neutral. They are placed near each other on aninsulated table. Sphere B is briefly touched with awire that is grounded. Which statement is correct?

A Sphere B remains neutral.

B Sphere B is now positively charged.

C Sphere B is now negatively charged.

D The charge on sphere B cannot be determinedwithout additional information.

E I need help

An

swer

https://njctl.org/video/?v=hhO_-8L37Qs

February 02, 2021

23 If a positively charged rod touches a neutralconducting sphere and is removed, what chargeremains on the sphere? What happens to themagnitude of the charge on the rod?

A The sphere becomes positive and therod's net charge stays the same.

B The sphere becomes positive and the rod'snet charge decreases.

C The sphere becomes negative and therod's net charge stays the same.

D The sphere remains neutral and therod's net charge stays the same.

E I need help

An

swer

https://njctl.org/video/?v=oC-4G2hTRV8

February 02, 2021

24 When the process of induction is used (a chargedrod approaching, but not touching the neutralsphere connected to ground), what is the sourceof the charge added to the neutral sphere?

A The charged rod.

B The air.

C The rod and the sphere share their charges.

D The Earth.

E I need help

An

swer

https://njctl.org/video/?v=PYpOqVjqMZI

February 02, 2021

25 Two identical neutral metal spheres are placed oninsulated stands. Describe an experiment that will allowyou to charge the spheres with equal and oppositeamounts of charge.

An

swer

https://njctl.org/video/?v=78MAIquSrf8

February 02, 2021

February 02, 2021


Electroscope

https://njctl.org/video/?v=pvEpupVBKK0

February 02, 2021

Gold Leaves

Conductor-

--

-+

+

++

+-+

-

The Electroscope

The electroscope measureselectrical charge (both signand magnitude). Theconductor rod is insulatedfrom the glass container.

When the scope is neutral,the leaves hang down to dueto their own mass.

Electroscopes can be charged by conduction or induction.

February 02, 2021

The Electroscope

An antique Electroscope from 1878.

{PD-US}

From the book "Opfindelsernes Bog" 1878 by AndréLütken

February 02, 2021

Charge = -4q


A neutral electroscope will becomenegatively charged when touched by anegatively charged object.

Negative electrical charge will distributeacross the electroscope and the goldleaves will repel, since they have thesame charge, and like charges repel.

--- -+ + + ---

-+

Neutrally Charged

Gold Leaves

Conductor-

--

-+

+

++

+-+

-

February 02, 2021


- -+ + +--+ - -+

+-+

+-

-+--

+-

-

+++

--

-+- -+

-

The bar is moved awayand there is a negativenet charge on thescope. Negative chargemoved from the rod tothe electroscope; therod has less negativecharge (Conservation ofCharge).

- -+ + +--+ - -

The gold leaves repel.

The leaves would also repel if the experimenthad been done with a positively charged bar.

February 02, 2021

26 When a negatively charged rod touches the top of aneutral electroscope, the gold leaves separate. What isthe charge on the leaves?

A Negative

B Positive

C Neutral

D Negative first, then changing to positive.

EI need help

An

swer

https://njctl.org/video/?v=aGqRN_Lyobw

February 02, 2021

February 02, 2021


A neutral electroscope can also be charged by induction.

If a bar with a negative net charge is brought near the scopethen the electrons in the electroscope will move down to theleaves and the leaves will repel. If the bar is removed, theleaves will go back to their original positions. This inductionis temporary - and no charge is transferred from the rod tothe leaves.

A similar effect is caused by a bar with a positive net charge.The leaves will again repel since like charges repel.

One more piece is needed to effect a permanent charge onthe electroscope.

Dem

o

https://njctl.org/video/?v=GRnhUB0GhP8

February 02, 2021

Electroscope charging by Induction

The missing piece is a ground. A neutral electroscope isconnected to ground and a negatively charged bar is broughtnear.

--- -+ + + ---

-+

initially neutral

-

--

-+

+

++

+

-

+-

negatively charged rod

February 02, 2021

-

+-+

--

++

---

++

-

--

+ +++-

--- -+ + + ---

-+

now positively charged - leaves repel each other

electrons travelintotheground

negatively charged

Electrons in the scope will berepelled out of the scope to theground. The scope will thenhave a positive net charge. Aswith charging a sphere byinduction, note that the chargeon the rod does NOT change.


February 02, 2021

-

+-+

--

--

---

--

--

+ +-+

-

-electrons travelout of theground

-+-

++ + + ---+

+

now negatively charged - leaves repel each other

positively charged

A similar effect occurs for a barwith a net positive charge;except the scope will end upwith a net negative chargesince electrons will come upfrom the ground to the scope.Again, the charge on the roddoes NOT change.


February 02, 2021


If the charging bar is removed while the ground is stillattached, the electrons will return either to the ground or tothe leaves until they have a neutral charge and will fall backtogether.

In order to leave the charge on the electroscope (and keepthe leaves separated), the ground must be removed beforethe charging bar.

The electrons will now have no place to go and a net positiveor negative charge will be left on the electroscope.

February 02, 2021

27 When an electroscope is charged via induction, what isthe source of the charge that moves to the gold leaves?

A A charged rod that gets near the electroscope.

B A charged rod that touches the electroscope.

C The glass surrounding the leaves.

D The ground (Earth).

EI need help

An

swer

https://njctl.org/video/?v=B7BpXRMGqN0

February 02, 2021

28 A positive object touches a neutral electroscope,and the leaves separate. Then a negative objectis brought near the electroscope, but does nottouch it. What happens to the leaves?

A They separate further.

B They move closer together.

C They are unaffected.

D Cannot be determined without additionalinformation.

E I need help

An

swer

https://njctl.org/video/?v=Hn30ViXQHKw

February 02, 2021

29 When charging an electroscope by induction, the leavesacquire a charge from the ground and separate. Howcould you keep the charge on the leaves which wouldkeep them separate from each other?

An

swer

https://njctl.org/video/?v=08lT8hZwoiY

February 02, 2021

February 02, 2021

Determining the type of chargeWhen the leaves of the electroscope repel, there is a chargepresent. It could be positive or negative.

The electroscope can also be used to find out the charge on theleaves. Take an object known to be positive or negative, place itnear the top of the scope, and watch the reaction.

https://njctl.org/video/?v=M1qNU_EaPc8

February 02, 2021

Determining the size of the Charge

Intuitively, it would seem that the further apart the leavesmove, the greater the magnitude (size) of the chargepresent.

This is true, and the next section will talk about the force dueto electric charges, which is responsible for the leavesmoving against the forces of gravity and tension.

electric charge

Documents