Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter...
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Transcript of Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter...
![Page 1: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/1.jpg)
Ch 18: Electric Force & Electric Fields
![Page 2: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/2.jpg)
The Origin of Electricity
• The electrical nature of matter comes from atomic structure
Nucleus – • made up of protons
and neutrons• Most of the mass of
the atom is contained in the nucleus
• mp=1.673x10-27kg
• mn=1.675x10-27kg
Electrons• Orbit the nucleus
in a “cloud”• Relatively mass-
less• me=9.11x10-31kg
![Page 3: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/3.jpg)
The Origin of Electricity
• The electrical nature of matter comes from atomic structure
Protons – • Have a positive
charge• +e = +1.60x10-19C
Electrons• Have a negative
charge• -e = -1.60x10-19C
Neutrons – • No net electrical
charge
![Page 4: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/4.jpg)
The Origin of Electricity
• The electrical nature of matter comes from atomic structure• The magnitude of the charge on a proton
= the magnitude of the charge on the electron. The magnitude is e=1.6x10-19 C.• e is an elementary charge (it is indivisible)• The SI unit for electrical charge is the
coulomb (C).
![Page 5: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/5.jpg)
The Coulomb
• The SI unit for electrical charge is the coulomb (C).• One coulomb is the charge which would flow
through a 120-watt light bulb in one second.• Two charges of 1 C each separated by a
meter would repel each other with a force of about 1,000,000 tons!• Usually, we measure charge in nano-
Coulombs (x10-9 C)
![Page 6: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/6.jpg)
Electrical Charge
• In nature, atoms are usually found with equal numbers of protons and electrons => electrically neutral• A net charge (q) can be built up on an
object by adding or removing electrons• q=Ne , where N is an integer
![Page 7: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/7.jpg)
Example 1
• How many electrons are there in one coulomb of negative charge?• q=Ne• N=q/e = 1.00C/1.60x10-19C• N=6.25x1018 electrons
![Page 8: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/8.jpg)
Charged objects & electrical force
• Electrons can be transferred from one object to another• The object that gains electrons
acquires a negative charge• The object that loses electrons has a
positive charge
![Page 9: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/9.jpg)
Charged objects & electrical force
•When a plastic rod is rubbed with fur, some of the electrons from the fur are transferred to the rod.• No electrons or protons are created or
destroyed• The net charge of the fur/rod system
remains constant (Law of conservation of electrical charge)
![Page 10: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/10.jpg)
Charged objects & electrical force
• Two electrically charged objects exert a force on each other.• This electrostatic force can alter the
motion of an object. (Newton’s 2nd Law)
![Page 11: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/11.jpg)
Example 2
• Object A and Object B are each electrically neutral. 2 million electrons are removed from A and placed on B. What is the resulting charge on A and B?• q=Ne• q=(2,000,000)(1.60x10-19C) = 3.2x10-13 C• A = +3.2x10-13 C• B = - 3.2x10-13 C
![Page 12: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/12.jpg)
Example 3
• Object A has a charge of -1.6x10-13C, and Object B is electrically neutral. 2 million electrons are removed from A and placed on B. What is the resulting charge on A and B?• q=Ne• q=(2,000,000)(1.60x10-19C) = 3.2x10-13 C• A = -1.6x10-13 C – (-3.2x10-13C) = +1.6x10-13C• B = 0C + (- 3.2x10-13 C) = - 3.2x10-13 C
![Page 13: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/13.jpg)
Conductors and Insulators
• Charge can exist on an object, and also move through an object.• Substances that readily conduct electric charge
are called electrical conductors. (ex: metals)•Materials that conduct electric charge poorly
are called electrical insulators. (example: rubber, plastic, wood)
![Page 14: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/14.jpg)
Remember chemistry???
• Recall that a metallic bond has a “sea of electrons”• The valence electrons are not “attached” to the
parent atom – they can wander freely throughout the material• The ready movement of valence electrons is
what makes a good conductor.
![Page 15: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/15.jpg)
Remember chemistry???
• In an insulator, there are very few electrons free to move throughout the material.• Insulators tend to have a more full valence shell
and higher ionization energies.• The valence electrons are being held tightly by
the nucleus of its parent atom. • Without the free electrons, there is very little
flow of charge electrical insulator
![Page 16: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/16.jpg)
Charging by contact
•When a negatively charged rod is touched to a metal sphere, some of the excess electrons from the rod are transferred to the sphere.• Once the rod is removed, the electrons repel
each other and spread out as far away from each other as possible.
![Page 17: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/17.jpg)
Charging by contact
• Identical conducting spheres equalize their charge upon touching.
+5q -3q
+5q -3q
+q+q
Total charge is +5q -3q = 2qequally distributed over both spheres
![Page 18: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/18.jpg)
Charging by induction
• A negatively charged rod that is brought close to (but not touching) a metal sphere induces the electrons in the sphere to move away from the negative rod causing a separation of charge.
![Page 19: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/19.jpg)
Charging by induction
• Grounding the sphere causes some of the electrons to leave the sphere and redistribute themselves over the earth (remember, they want to be as far away from each other as possible. The earth is a good conductor.)
![Page 20: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/20.jpg)
Charging by induction
• If the grounding wire is removed, then the negative rod is removed, the sphere is left with a positive net charge.
![Page 21: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/21.jpg)
Charging by induction
• If the sphere were made of an insulating material (like plastic), you would not be able to induce a net charge on it.• However, you would still be able to separate
the positive and negative charges slightly and induce a slight positive charge at the surface.
![Page 22: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/22.jpg)
Example 4
• A rod made from insulating material carries a net charge (which may be positive or negative), whereas a copper sphere is electrically neutral. The rod is held close to the sphere but does not touch it. Which statement is true?• A) the forces are always attractive• B) the forces are always repulsive• C) the forces are attractive when the rod is negative and
repulsive when positive• D) the forces are repulsive when the rod is negative and
attractive when positive• E) there are no forces
![Page 23: Ch 18: Electric Force & Electric Fields. The Origin of Electricity The electrical nature of matter comes from atomic structure Nucleus – made up of protons.](https://reader036.fdocuments.in/reader036/viewer/2022062421/56649d305503460f94a08132/html5/thumbnails/23.jpg)
Assignment
•Focus p. 563 #1,2, 4•Problems #1-6