Chapter 33 Flashcards
What type of field is the force field that surrounds a mass?
a gravitational field
What type of path does a ball take when you throw it in the air?
a curved path
In earlier chapters, what was the explanation for a curved path?
there is an interaction between the ball and earth - between their centers of gravity
What idea bothered Isaac Newton and others?
The idea that things not in contact could exert a force on tings without touching them.
Why does a ball curve?
The ball interacts with Earth’s gravitational field
What causes a field?
The mass of an object.
Just as the space around Earth and every other mass is filled with a __________ field, the space around every electric charge is filled with an __________ field.
gravitational; electrical
What is an electric field?
a force field that surrounds an electric charge or group of charges.
What does an electrical force hold in place?
an electron in orbit about a proton.
There is no contact between the objects, and the forces are…
acting at a distance
The satellite and electron interact with the _____ _____ of the planet and the proton and are everywhere in ______ with these fields.
force; fields; contact
The force that one electric charge exerts on another can be described as the…
interaction between one charge and the electric field set up by the other
An electric field has both magnitude and direction. True or False?
True
The magnitude (strength) of an electric field can be measured by…
its effect on charges located in the field
Where the force is greatest on the test charge (a small positive test charge), the field is ________. Where the force on the test charge is weak, the field is ______.
strongest; small
The direction of an electric field at any point, by convention, is…
the direction of the electrical force on a small positive test charge placed at that point
If the charge that sets up the field is positive, the field…
points away from that charge
An electric field is a scalar quantity. True or false?
false, it is a vector quantity
The magnitude of the field is indicated by…
the length of the vectors.
The electric field is greater where…
the vectors are long than it is where the vectors are short.
You can use electric field lines (also called lines of force) to represent an electric field. Where the lines are ______ apart, the field is weaker.
farther
For an isolated charge, the lines extend to…
infinity
For two or more opposite charges, the lines…
emanate from a positive charge and terminate on a negative charge
Why is the occupant in the car and the car safe when it was struck by lightning?
The electrons that shower down upon the car are mutually repelled and spread over the outer metal surface, finally discharging when additional sparks jump from the car’s body to the ground. The configuration of electrons on the car’s surface at any moment is such that the electric fields inside the car practically cancel to zero. This is true of any charged conductor.
If the charge on a conductor is not moving, then…
the electric field inside the conductor is zero.
The absence of electric field within a conductor holding static charge does not arise from…
the inability of an electric field to penetrate metals.
Where does the absence of electric field within a conductor holding static charge does arise from?
It comes about because free electrons within the conductor can “settle” and stop moving only when the electric field is zero. So the charges arrange themselves to ensure a zero field within the material.
Because of mutual repulsion…
The electrons spread as far apart from one another as possible. They distribute themselves uniformly over the surface of the sphere.
A positive test charge located exactly in the middle of the sphere would feel…
no force
The electrons on the left side of the sphere would tend to pull the positive test charge to the left but the electrons on the right side of the sphere would…
tend to pull the test charge to the right, equally as hard. This makes the net charge zero on the test charge.
Cancellation cannot occur anywhere inside the sphere. True or false.
False
If the conductor is not spherical, then…
the charge distribution will not be uniform
The exact charge distribution over the surface is such as that the electrical field inside the conductor is…
zero
If there were an electrical field inside a conductor then free electrons inside the conductor would be set in motion. How far would they move?
Until equilibrium is establised
Can you shield gravity?
No, because gravity only attracts
How can you shield electric fields?
Surround yourself or whatever you wish to shield with a conducting surface, Put this surface in an electric field of whatever field strength, The free charges in the conductor in a way such that all field contributions inside cancel one another.
What is work required to do?
To push a charged particle against the electrical field of a charged body
The electrical potential energy of a charged particle is __________ when work is done to push it against the __________ ________ of something else that is charged.
increased; electrical; field
The work is equal to…
the energy gained by the charge
Electrical potential energy
The energy a charge has due to its location in an electric field
If the charge, gained by electrical potential energy, is released…
It will accelerate in a direction away from the sphere, and its electrical potential energy will transform into kinetic energy
If we push two charges instead…
we do twice as much as work
The two charges in the same location will have ______ the electrical potential energy as one; a group of ten charges will have _____ times the potential energy
twice; ten
What is the electrical potential energy per charge?
the total electrical potential energy divided by the amount of charge
At any location the potential energy per charge will be…
the same
What is electric potential?
the concept of electrical potential energy per charge
Electric potential is the same as electric potential energy. True or False?
False
What is the SI unit of measurement for electric potential?
the volt
Who was the volt named after?
the Italian physicist Allesandro Volta (1745-1827)
What is the formula for volt?
Volt=1 joule/coulomb
What is voltage?
Electric potential measured in volts
What is the significance of voltage?
Is that once the location of zero voltage has been specified.
Is one coulomb a very large amount of charge?
Yes
A high voltage requires…
great energy only if a great amount of charge is involved
What is a capacitor?
Electrical energy can be stored in this common device
Where are capacitors found?
In nearly all electronic circuits
Capacitors in photoflash units store…
larger amounts of energy slowly and release it rapidly during the short duration of the flash
Enormous amounts of energy are stored in…
banks of capacitors that power giant lasers in national laboratories
What is the simplest capacitor?
A pair of conducting plates separated by a small distance, but not touching each other.
When the plates are connected to a charging device…
charge is transferred from one plate to another.
As the positive battery terminal pulls electrons from the plate connected to it…
These electrons in effect are pumped through the battery asn through the negative terminal to the opposite plate. Thr capacitor plates then have equal and opposite charges.
The positive plate is connected to the…
positive battery terminal
The negative plate is connected to the…
negative battery terminal
When is the charging process complete?
When the potential difference between the plates equals the potential difference between the battery terminals
The greater the battery voltage and the larger and closer the plates…
the greater the charge that is stored
Capacitors store and hold…
electric charges until discharged
When is a charged capacitor discharged?
When a conducting path is provided between the plates
Can a capacitor store charge even after the electricity to a device has been turned off?
Yes
The energy stored in a capacitor comes from…
work done to charge it
The energy is in the form of…
the electric field between its plates
Where is the energy stored in a capacitor stored?
In the electric field
What are store houses of energy?
electric fields
What is the Van de Graaff generator?
a common laboratory device for buidling up high voltages
