Physics Chapters 32 and 33, Electricity and Magnetism!
If the charge on a conductor is not moving, the electric field inside the conductor is exactly _____
zero
The SI unit of charge is the _______.
coulomb
If you scuff electrons onto your shoes while walking across a rug, are you negatively or positively charged?
Neg
Write an equation that expresses the relationship between volts, joules, and coulombs.
1 volt = 1 joule/1 coulomb
If an electron at a certain distance from a charged particle is attracted with a certain force, how will the force compare at twice this distance? Is the charged particle in this case positive or negative?
(According to the inverse-square law), at twice the distance the force will be 1/4 as much.
How many electrons are contained in 1 C of charge?
6.24 times 10^18
The charge of 1 C(Coulomb) is...
6.24 times 10^18 electrons
Why is the process illustrated in the figure an example of charging by induction?
A charged object charged each of the spheres without touching them.
Why do the positive and negative charges separate in part (b)?
A negatively charged rod near sphere A repels electrons, and excess negative charge moves onto sphere B, leaving sphere A with excess positive charge.
Different materials have different _________ for electrons
Affinities
Circle each letter next to a discovery made by Benjamin Franklin. a. electricity b. Lightning is an electrical phenomenon. c. lightning rods d. Electricity can travel along metal wires.
B, C
Why don't you feel the electrical forces that act on you all the time?
Both repelling and attracting forces act on you, and the forces cancel each other out.
Circle the letter beside the sentence that explains why a charged comb attracts an uncharged piece of paper. a. The forces of attraction and repulsion on opposite sides of the paper cancel. b. The forces of attraction and repulsion on the paper disappear with the comb nearby. c. The force of attraction for the closer charge is greater than the force of repulsion for the farther charge. d. The force of repulsion for the closer charge is greater than the force of attraction for the farther charge.
C.
______ is the fundamental electrical property to which the mutual attractions or repulsions between electrons or protons is attributed.
Charge
What is an ion? What are the two types?
Charged atom. Positive (net positive, lost one or more electrons). Negative (net negative, gained one or more electrons)
Triboelectric effect/ triboelectric charging
Contact electrification on which certain materials become electrically charged after they come into fractional contact with another material
How do you find out the charge of an atom with a charge diagram?
Count number of protons and electrons, see which one has the most 5+ 3- ---- 2+ Subtract small number from big number
How can we change the charge of an object?
Move electrons from one object to another 1. Conduction 2. Induction 3. Friction
What is electric potential?
Electric potential is electrical potential energy per charge.
Why don't you float off into space?
Electrical repelling force and electrical attracting force balance each other out, leaving gravity, the weaker force, which keeps you tethered to the Earth.
What is the principle of conservation of charge?
Electrons are neither created nor destroyed but are simply transferred from one material to another.
If fur and a metal rod are rubbed together, what happens?
Electrons from fur --> rod, rod becomes neg charged
How does an object have no net charge?
Equal number of electrons and protons
Coulomb's Law (equation)
F = k x q1 x q2 / r^2 k - 9.0 x 10^9 Nm^2/C^2 q1 and q2 - quantity of charged particles d = distance between charged particles
Is the following sentence true or false? A lightning rod placed above a building repels electrons in the air to prevent leaking of the charge onto the ground.
FALSE
Is the following statement true or false? The direction of an electric field at any point, by convention, is the direction of the electrical force on a small negative test charge, placed at that point.
FALSE
What does Coulomb's law state?
For charged particles or objects that are small compared with the distance between them, the force between the charges varies directly as the product of the charges and inversely as the square of the distance between them.
Coulomb's Law
For small objects... the relationship between electrical force, charges, and distance. Varies from product of charges and inversely as the square of the distance between them
What tends to lose electrons?
Fur, glass, hair, wool
The ______ is a practically infinite reservoir for electric charge
GROUND
Why is G a smaller number than k?
Gravity is a weaker force than electrical force
Classify the following by writing C beside each conductor, I beside each insulator, and S beside each semiconductor. RUBBER
INSULATOR
Classify the following by writing C beside each conductor, I beside each insulator, and S beside each semiconductor. Glass
Insulator
Why is the water molecule shown in the figure above an electric dipole?
It has a little more negative charge on one side than the other.
The fundamental rule at the base of all electrical phenomena
Like charges repel and opposites attract
Describe an electrically polarized atom or molecule.
One side of the atom or molecule is slightly more positive (or negative) than the positive opposite side.
Which electrons transfer?
Outermost, loosely bound
What tends to gain electrons?
Rubber, sulfur, metal
What are two applications of capacitors?
Sample answer: Capacitors are used in computer memories, some computer keyboards, photoflashes, and giant lasers in national laboratories.
Classify the following by writing C beside each conductor, I beside each insulator, and S beside each semiconductor. Germanium
Semiconductor
Is the following sentence true or false? In a vector representation of an electric field, the magnitude of an electric field is indicated by the length of the vector arrows.
TRUE
Describe the simple model of the atom proposed in the early 1900s by Rutherford and Bohr.
The atom has a positively charged nucleus surrounded by electrons. The protons attract and hold the electrons in orbit.
Consider the electric field around a small positive charge. How can you describe the direction of the field?
The field points away from the charge.
What is charge?
The fundamental electrical property to which the mutual attractions or repulsions between electrons or protons is attributed to
What effect will adding an impurity level of one atom in ten million to a crystal of semiconductor have?
The impurity adds or removes an electron from the crystal structure, which increases conductivity.
Why do the positive and negative charges spread out on each on the spheres in part (d)?
The like charges repel each other on each of the spheres.
How can the magnitude of an electric field be measured?
The magnitude of an electric field can be measured by its effect on charges located in the field
Describe what causes lightning to occur during thunderstorms.
The negatively charged bottoms of clouds induce a positive charge on the surface of Earth below. Lightning can occur as an electrical discharge between the clouds and the oppositely charged ground below.
The diagram shows a simple capacitor. Explain how the capacitor is charged.
The positive battery terminal pulls electrons from the plate connected to it. These electrons are pumped through the battery and through the negative terminal to the opposite plate. The capacitor plates then have equal and opposite charges. The charging process is complete when the potential difference between the plates equals the potential difference between the battery terminals—the battery voltage.
How can the voltage of a Van de Graaff generator be increased?
The voltage of a Van de Graaff generator can be increased by increasing the radius of the sphere or by placing the entire system in a container filled with high-pressure gas.
Explain why there is no net charge in a neutral atom.
There are as many electrons as protons. The positive and negative charges balance.
Why can an insulator become polarized when you bring a conducting rod near it?
There are no free electrons to migrate through the insulating material. Instead, there is a rearrangement of the positions of charges within the atoms and molecules.
Why are some electronic components and some cables encased in a metal covering?
They are encased in metal to shield them from all outside electrical activity.
Explain why the bits of paper sometimes suddenly fly off when a comb attracts bits of uncharged paper.
This indicates charging by contact. The paper bits have acquired the same sign of charge as the comb, and are then repelled.
How does an object become electrically charged?
Unequal number of electrons and protons
Since an electric field has both magnitude and direction, it is a __________
VECTOR QUANTITY
The charge of an object is the _______ of the charge of an electron
Whole-number multiple
What is an electric field?
a force field that surrounds an electric charge or group of charges
What is voltage?
a measure of electric potential, expressed in volts
Classify each of the following by writing F if it is an example of charging an object by friction and C if it is an example of charging an object by contact. a. sliding across the seat of an automobile b. scuffing your shoes as you walk across a rug c. touching a charged rod to a metal sphere d. combing your hair with a plastic comb e. touching your hand to a slightly charged metal plate
a. F b. F c. C d. F e. C
One object charges a second object by contact. Describe what will happen to the charge on the second object in each of the cases below. a. The second object is a good conductor. b. The second object is a poor conductor
a. The charge will spread to all parts of the second object's surface. b. The extra charge will stay close to where the second object was touched.
What are the three ways objects can become electrically charged? a. b. c.
a. friction b. contact c. induction
By convention, what is the charge of the following? a. electrons b. protons c. neutrons
a. negative b. positive c. neutral
The _________ of many atoms are bound very loosely to an atom and can be easily dislodged. Circle the correct answer. a. outermost electrons b. innermost electrons c. outermost protons d. innermost protons
a. outermost electrons
What is static electricity?
an imbalance of electric charge on the surface of an object Charges only build in one area
Circle the letter of each statement that is true about charged conductors. a. The absence of an electric field within a conductor holding static charge arises from the inability of an electric field to penetrate metals. b. The absence of an electric field comes about because free electrons within the conductor stop moving when the electric field is zero. c. The charges arrange themselves to ensure a zero field within the material. d. If the conductor is not spherical, then the charge distribution will not be uniform.
b, c, d
Circle the letter of each statement that is true. a. No work is required to push a charged particle against the electric field of a charged body. b. The electrical potential energy of a charged particle decreases when work is done to push it against the electric field of something else that is charged. c. The energy a charge has due to its location in an electric field is called electrical potential energy. d. If a charge with electrical potential energy is released, its electrical potential energy will transform into kinetic energy
c, d
A charged capacitor is discharged when a ____________ is provided between the plates.
conducting path
Classify the following by writing C beside each conductor, I beside each insulator, and S beside each semiconductor. ALUMINUM
conductor
Classify the following by writing C beside each conductor, I beside each insulator, and S beside each semiconductor. COPPER
conductor
Match each variable or constant in Newton's law of gravitation with its analogous variable or constant in Coulomb's law. d
d
Circle the letter beside the correct comparison of the strengths of the gravitational force and the electrical force. a. The gravitational force is slightly stronger than the electrical force. b. The electrical force is slightly stronger than the gravitational force. c. The gravitational force is much stronger than the electrical force. d. The electrical force is much stronger than the gravitational force
d. The electrical force is much stronger than the gravitational force.
Circle the letter beside the correct comparison of the magnitudes of the charges of a proton and an electron. a. The magnitude of the proton's charge is slightly greater. b. The magnitude of the electron's charge is slightly greater. c. The magnitudes of a proton's charge and an electron's charge are always equal, but they vary for different atoms. d. The magnitudes of a proton's charge and an electron's charge are always equal and never change.
d. The magnitudes of a proton's charge and an electron's charge are always equal and never change.
What does electrostatics involve?
electric charges, the forces between them, and their behavior in materials
A material through which electric charge can flow is a(n) _______________.
electric conductor
A material that is a poor conductor of electricity is a(n) ____________.
electric insulator
What is conservation of charge?
electrons are neither created nor destroyed but are simply transferred from one material to another
Is the following sentence true or false? In a Van de Graaff generator, as electrons leak off the belt and onto the conducting sphere, the electric field inside the sphere steadily increases in magnitude.
false
Is the following sentence true or false? The electrical force between two protons is very small compared to the gravitational force.
false
Electric fields can also be described by using field lines (or lines of force). In a field lines representation of an electric field, the field is weaker where the lines are __________
farther apart
A charged atom is called a(n) ________.
ion
Match each variable or constant in Newton's law of gravitation with its analogous variable or constant in Coulomb's law. G
k
Like a gravitational field, an electric field has both ________ and ________.
magnitude, direction
Define semiconductor.
material that can be made to behave sometimes as insulators and sometimes as conductors
If a rubber rod is rubbed by a piece of fur, the rubber becomes ________ charged and the fur becomes ________ charged.
negatively, positively
Electrons are _________ charged and protons are _________ charged, neutrons are _____ charged
negatively, positively, neutrally
When you rub an inflated balloon on your hair and it becomes negatively charged, the charge on the balloon induces a _________ charge on the surface of the wall.
positive
Match each variable or constant in Newton's law of gravitation with its analogous variable or constant in Coulomb's law. m1
q1
Match each variable or constant in Newton's law of gravitation with its analogous variable or constant in Coulomb's law. m2
q2
Like charges ______ and opposite charges ________.
repel, attract
Classify the following by writing C beside each conductor, I beside each insulator, and S beside each semiconductor. Silicon
semiconductor
Law of electric charges
the law that states that like charges repel and opposite charges attract. Charged objects attract neutral objects
The energy stored in a capacitor comes from the _____ done to charge it.
work
Friction
the transfer of electrons between the two objects that are rubbed together resulting in one neg and one pos charged object
Thin layers of semiconducting materials sandwiched together make up __________, which are used in a variety of electrical applications.
transistors
Is the following sentence true or false? A charged object has potential energy by virtue of its location in an electric field.
true
Is the following sentence true or false? Atoms in a semiconductor hold their electrons until the atoms of the semiconductor are given small energy boosts.
true
Is the following sentence true or false? Electric potential is not the same as electrical potential energy
true
Is the following sentence true or false? The mass of a proton is 2000 times greater than the mass of an electron.
true
The SI unit of measurement for electric potential is the ____
volt
