PhysicsChpt21物理双语课件
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CPO Science Foundations of Physics
Unit 7, Chapter 21
Chapter 21 Electric Charges and Forces
21.1 Electric Charge 21.2 Coulomb’s Law 21.3 Capacitors
Unit 7: Electricity and Magnetism
1. Describe and calculate the forces between like and unlike electric charges. 2. Identify the parts of the atom that carry electric charge. 3. Apply the concept of an electric field to describe how charges exert force on other charges. 4. Sketch the electric field around a positive or negative point charge.
Two coulombs of charge pass through a wire in five seconds. Calculate the current in the wire.
21.1 Conductors and insulators
All materials contain electrons.
21.1 Electric Charge
Electric charge is a property of tiny particles in atoms.
The unit of electric charge is the coulomb (C). A quantity of charge should always be identified with a positive or a negative sign.
21.1 Coulomb's Law
The force between charges is directly proportional to the magnitude, or amount, of each charge. Doubling one charge doubles the force. Doubling both charges quadruples the force.
This is called charging by friction.
Objects charged by this method will attract each other.
21.2 Coulomb's Law
Coulomb’s law relates the force between two single charges separated by a distance.
Chapter 21 Vocabulary Terms
charge electrically neutral static electricity positive charge negative charge electric forces charge by friction electroscope protons neutrons electrons gravitational field charged induction Coulomb’s law capacitor parallel plate capacitor microfarad coulomb electric field capacitance charge polarization shielding test charge farad field inverse square law discharged field lines
21.1 Electric forces
The forces between the two kinds of charge can be observed with an electroscope.
21.1 Electric forces
Charge can be transferred by conduction.
The electrons are what carry the current in a conductor. The electrons in insulators are not free to move—they are tightly bound inside atoms.
21.1 Conductors and insulators
21.1 Electric forces
Electric forces are created between all electric charges.
Because there are two kinds of charge (positive and negative) the electrical force between charges can attract or repel.
21.2 Calculating force
Two balls are each given a static electric charge of one ten-thousandth (0.0001) of a coulomb.
Calculate the force between the charges when they are separated by one-tenth (0.1) of a meter. Compare the force with the weight of an average 70 kg person.
21.1 Electric current
The direction of current was historically defined as the direction that positive charges move. Both positive and negative charges can carry current. In conductive liquids (salt water) both positive and negative charges carry current. In solid metal conductors, only the electrons can move, so current is carried by the flow of negative electrons.
21.2 Coulomb's Law
The force between two charges is directed along the line connecting their centers.
Electric forces always occur in pairs according to Newton’s third law, like all forces.
A semiconductor has a few free electrons and atoms with bound electrons that act as insulators.
21.1 Conductors and insulators
When two neutral objects are rubbed together, charge is transferred from one to the other and the objects become oppositely charged.
Constant 9 x109 N.m2/C2
Force (N)
F = K q1 q2 r2
Charges (C)
Distance (m)
21.2 Coulomb's Law
The force between two charges gets stronger as the charges move closer together. The force also gets stronger if the amount of charge becomes larger.
21.1 Electric Charge
Key Question: How do electric charges interact?
*Students read Section 21.1 AFTER Investigation 21.1
21.1 Electric Charge
All ordinary matter contains both positive and negative charge.
21.1 Electric Charge
Objects can lose or gain electric charges. The net charge is also sometimes called excess charge because a charged object has an excess of either positive or negative charges. A tiny imbalance in either positive or negative charge on an object is the cause of static electricity.
Chapter 21 Objectives
5. Describe how a conductor shields electric fields from its interior.
6. Describe the voltage and current in a circuit with a battery, switch, resistor, and capacitor. 7. Calculate the charge stored in a capacitor.
You do not usually notice the charge because most matter contains the exact same number of positive and negative charges. An object is electrically neutral when it has equal amounts of both types of charge.
21.1 Coulomb's Law
The force between charges is inversely proportional to the square of the distance between them. Doubling the distance reduces the force by a factor of 22 = (4), decreasing the force to one-fourth its original value (1/4). This relationship is called an inverse square law because force and distance follow an inverse square relationship.
21.1 Electric current
Current is the movement of electric charge through a substance.
Current (amps)
I=q t
Charge源自文库that flows (coulombs)
Time (sec)
21.1 Calculate current
Unit 7, Chapter 21
Chapter 21 Electric Charges and Forces
21.1 Electric Charge 21.2 Coulomb’s Law 21.3 Capacitors
Unit 7: Electricity and Magnetism
1. Describe and calculate the forces between like and unlike electric charges. 2. Identify the parts of the atom that carry electric charge. 3. Apply the concept of an electric field to describe how charges exert force on other charges. 4. Sketch the electric field around a positive or negative point charge.
Two coulombs of charge pass through a wire in five seconds. Calculate the current in the wire.
21.1 Conductors and insulators
All materials contain electrons.
21.1 Electric Charge
Electric charge is a property of tiny particles in atoms.
The unit of electric charge is the coulomb (C). A quantity of charge should always be identified with a positive or a negative sign.
21.1 Coulomb's Law
The force between charges is directly proportional to the magnitude, or amount, of each charge. Doubling one charge doubles the force. Doubling both charges quadruples the force.
This is called charging by friction.
Objects charged by this method will attract each other.
21.2 Coulomb's Law
Coulomb’s law relates the force between two single charges separated by a distance.
Chapter 21 Vocabulary Terms
charge electrically neutral static electricity positive charge negative charge electric forces charge by friction electroscope protons neutrons electrons gravitational field charged induction Coulomb’s law capacitor parallel plate capacitor microfarad coulomb electric field capacitance charge polarization shielding test charge farad field inverse square law discharged field lines
21.1 Electric forces
The forces between the two kinds of charge can be observed with an electroscope.
21.1 Electric forces
Charge can be transferred by conduction.
The electrons are what carry the current in a conductor. The electrons in insulators are not free to move—they are tightly bound inside atoms.
21.1 Conductors and insulators
21.1 Electric forces
Electric forces are created between all electric charges.
Because there are two kinds of charge (positive and negative) the electrical force between charges can attract or repel.
21.2 Calculating force
Two balls are each given a static electric charge of one ten-thousandth (0.0001) of a coulomb.
Calculate the force between the charges when they are separated by one-tenth (0.1) of a meter. Compare the force with the weight of an average 70 kg person.
21.1 Electric current
The direction of current was historically defined as the direction that positive charges move. Both positive and negative charges can carry current. In conductive liquids (salt water) both positive and negative charges carry current. In solid metal conductors, only the electrons can move, so current is carried by the flow of negative electrons.
21.2 Coulomb's Law
The force between two charges is directed along the line connecting their centers.
Electric forces always occur in pairs according to Newton’s third law, like all forces.
A semiconductor has a few free electrons and atoms with bound electrons that act as insulators.
21.1 Conductors and insulators
When two neutral objects are rubbed together, charge is transferred from one to the other and the objects become oppositely charged.
Constant 9 x109 N.m2/C2
Force (N)
F = K q1 q2 r2
Charges (C)
Distance (m)
21.2 Coulomb's Law
The force between two charges gets stronger as the charges move closer together. The force also gets stronger if the amount of charge becomes larger.
21.1 Electric Charge
Key Question: How do electric charges interact?
*Students read Section 21.1 AFTER Investigation 21.1
21.1 Electric Charge
All ordinary matter contains both positive and negative charge.
21.1 Electric Charge
Objects can lose or gain electric charges. The net charge is also sometimes called excess charge because a charged object has an excess of either positive or negative charges. A tiny imbalance in either positive or negative charge on an object is the cause of static electricity.
Chapter 21 Objectives
5. Describe how a conductor shields electric fields from its interior.
6. Describe the voltage and current in a circuit with a battery, switch, resistor, and capacitor. 7. Calculate the charge stored in a capacitor.
You do not usually notice the charge because most matter contains the exact same number of positive and negative charges. An object is electrically neutral when it has equal amounts of both types of charge.
21.1 Coulomb's Law
The force between charges is inversely proportional to the square of the distance between them. Doubling the distance reduces the force by a factor of 22 = (4), decreasing the force to one-fourth its original value (1/4). This relationship is called an inverse square law because force and distance follow an inverse square relationship.
21.1 Electric current
Current is the movement of electric charge through a substance.
Current (amps)
I=q t
Charge源自文库that flows (coulombs)
Time (sec)
21.1 Calculate current