Physics MT7.1 (Static Electricity)
Over the years, scientists have determined that there are two types of electric charges. _______________ called them positive and negative charges.
Benjamin Franklin
____________________. That is, individual charges never are created or destroyed. All that happens is that the positive and negative charges are separated through a transfer of electrons.
Charge is conserved
K = ________________________ = 9.0 x 109 N•m2/C2
Coulomb's Constant
If, and only if, the charge q is a point charge or a uniformly charged sphere, you can calculate its electric field from ________________.
Coulomb's law
_________________: the magnitude of the force between two point charges qA and qB, (in coulombs) a distance r (in meters) apart can be written as follows: F= K * qAqB/r(squared)
Coulomb's law
According to _________________, the force is directly proportional to the strength of the test charge (q'), so the ratio of the force to the strength of the test charge is a ___________.
Coulomb's law --- constant
What is Coulomb's law, and how is it used?
Coulomb's law states that: The magnitude of the electrostatic force of attraction or repulsion between two point charges is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between them. The force is along the straight line joining them.
____________________: property of the space around a charged object that exerts forces on other charged objects.
Electric field
_________________ are directed toward negative charges and away from positive charges.
Electric field lines
___________________ is the study of electric charges that can be collected and held in one place.
Electrostatics
How are charge, electric field, and forces on charged objects related?
In an electric field a charged particle, or charged object, experiences a force. If the forces acting on any object are unbalanced, it will cause the object to accelerate. With this in mind: If two objects with the same charge are brought towards each other the force produced will be repulsive, it will push them apart.
How can you demonstrate that charged objects exert forces, both attractive and repulsive?
In contrast to the attractive force between two objects with opposite charges, two objects that are of like charge will repel each other. That is, a positively charged object will exert a repulsive force upon a second positively charged object. This repulsive force will push the two objects apart.
How does the electrostatic force depend on the distance between charges?
In electrostatics, the electrical force between two charged objects is inversely related to the distance of separation between the two objects. Increasing the separation distance between objects decreases the force of attraction or repulsion between the objects.
How can you charge objects by conduction and by induction?
In this process, a charged object is brought near but not touched to a neutral conducting object. The presence of a charged object near a neutral conductor will induce (force) electrons within the conductor to move. The movement of electrons leaves an imbalance of charge on opposite sides of the neutral conductor.
_________ are good conductors because at least one electron on each atom can be removed easily. These electrons move freely throughout the piece of metal.
Metals
________________ is the charge of 6.24×1018 electrons or protons.
One coulomb
How do we know that charging is the separation, not the creation, of electric charges?
Separating Charges Atoms start out with the same number of negative charges (electrons), and positive charges (protons). Conversely, adding electrons to an atom would result in a negative ion. If you do this enough times, you can make an object positive or negative. Friction is one of the ways to separate charge.
How can you represent electric fields in diagrams and other models?
Since electric field is a vector quantity, it can be represented by a vector arrow. For any given location, the arrows point in the direction of the electric field and their length is proportional to the strength of the electric field at that location. Such vector arrows are shown in the diagram below.
applications are designed to avoid the buildup of static charge and to safely eliminate any charge that does build up. ______________________________
Static charge can ruin film if it attracts dust, and electronic equipment can be damaged by the discharge of static charge.
What are the differences between conductors and insulators?
The most common difference between the two is that while conductors allow free flow of electrons from one atom to another, insulators restrict free flow of electrons. Conductors allow electrical energy to pass through them, whereas insulators do not allow electrical energy to pass through them.
The results of experiments and the actions of the charged rods can be summarized in the following way: _______________
There are two kinds of electric charges: positive and negative. Charges exert forces on other charges at a distance. The force is stronger when the charges are closer together. Like charges repel; opposite charges attract.
There are many applications of electric forces on particles. _______________________________
Used to collect soot in smokestacks, thereby reducing air pollution Tiny paint droplets, charged by induction, can be used to paint automobiles and other objects very uniformly. Photocopy machines use static electricity to place black toner on a page so that a precise reproduction of the original document is made.
In a _________________, a belt is driven by two rollers or pulleys. When the roller attached to the base rotates, the belt moves. The roller builds up a strong negative net charge, and the belt builds a weaker positive net charge. The roller's electric field repels electrons in the tips of a nearby brush assembly, causing the tips of the brushes to become positively charged. At the same time, the roller's electric field strips electrons from nearby molecules in the air. These electrons are attracted to the positively charged tips of the brush. The positive ions from the air move toward the negatively charged roller but collect on the belt and are transported to the metal dome. When a person touches the metal dome, the positively charged dome attracts the electrons in the person's body, causing the person's hair to become positively charged. The individual hairs repel each other and align with the electric field around the person's head.
Van de Graaff generator
What is an electric field?
a region around a charged particle or object within which a force would be exerted on other charged particles or objects.
You can envision the force from an electric field by modeling its effects on a small charged object—________________—at some location.
a test charge (q')
When more than one electric charge is present, the electric fields ________________.
add together
With the ______________ of energy, the outer electrons can be removed from atoms.
addition
lightning discharges a thundercloud. In both of these cases, _____________ became a conductor for a brief moment. Excess charges in the cloud and on the ground are great enough to remove electrons from the molecules in the air.
air
You _____________ an electric field, but there are ways to detect that an electric field is present.
cannot see
Forces between charged particles are mathematically related to ________________.
charge and distance
Charging a neutral body by touching it with a charged body, is called ________________________.
charging by conduction
The process of charging a neutral object by bringing a charged object near it is called ___________________.
charging by induction
The force is stronger when the charges are___________________.
closer together
Under certain conditions, charges move through air as if it were a _______________.
conductor
The SI standard unit of charge is called the _________________.
coulomb (C)
The electric force, like all other forces, is a vector quantity. Force vectors need both a magnitude and a direction. However, the Coulomb's law equation gives only the magnitude of the force. To determine the ___________, you need to draw a diagram and interpret charge relations carefully.
direction
The spark that jumps between your finger and a doorknob after you have rubbed your feet on a carpet ________________ you. In other words, you have become neutral because the excess charges have left you.
discharges
Charges exert forces on other charges at a ________________.
distance
Electroscopes are sensitive and useful for determining ________________.
electric charge
A material that allows charges to move about easily is called an _________________.
electric conductor
An ____________________ is a property of the space around a charged object that exerts forces on other charged objects.
electric field
The ___________________ at point A, the location of q' is represented by E=F(little)on q' /q'
electric field
You can represent electric fields with ____________________. An electric field line indicates the direction of the force due to the electric field on a positive test charge.
electric field lines
The ______________________, like all other forces, is a vector quantity. Force vectors need both a magnitude and a direction.
electric force
A material through which a charge will not move easily is called an ________________.
electric insulator
All materials contain light, negatively charged particles called ___________. In addition, each atom has a massive, positively charged nucleus.
electrons
If two neutral objects are rubbed together, each can become charged. For instance, when rubber shoes are rubbed on a wool rug, ____________ are removed from the atoms in the wool and transferred to the shoes. The extra electrons on the rubber result in a net negative charge. The electrons missing from the wool result in a net positive charge.
electrons
When a negatively charged rod is touched to the knob of an electroscope, _________________ are added to the electroscope.
electrons
An _______________ consists of a metal knob connected by a metal stem to two thin, lightweight pieces of metal foil, called leaves.
electroscope
If there is an ________________on the object, then there is an electric field at that point.
electrostatic force
If you rub your hair with a balloon, it will stand on end because of the __________________ between your hair and the oppositely charged balloon.
electrostatic force
The _______________________ can be demonstrated by suspending a charged rod so that it turns easily.
electrostatic force
Michael Faraday suggested the idea of a force ___________ to explain how the electric force can act at a distance.
field
You can make a model of an electric field by using arrows to represent the field vectors at various locations. The arrow's length represents the ________________. The direction of the arrow represents the ______________.
field strength --- field direction
The process of removing excess charge by connecting an object to Earth is called _______________.
grounding
... two thin, lightweight pieces of metal foil, called __________ .
leaves
Two objects with ______ charges always repel each other.
like
The ________________ of the electric field is newtons per coulomb (N/C).
magnitude
The electric force, like all other forces, is a vector quantity. Force vectors need both a magnitude and a direction. However, the Coulomb's law equation gives only the ______________ of the force.
magnitude
You can use a test charge to __________ the electric field resulting from any collection of test charges.
map
From a _______________________, acquiring charge is a process of transferring electrons.
microscopic viewpoint
The spacing between the lines indicates the electric field's strength. The field is stronger where the lines are spaced ___________________.
more closely
The freed electrons can remain unattached or become attached to other atoms, resulting in ________________ charged particles.
negatively
the two leaves are charged _________________ and repel each other; therefore, they spread apart.
negatively
A test charge should be small enough so that its effect on the charge you are testing (q) is ____________.
negligible
For a ____________ object, the amount of negative charge exactly balances the amount of positive charge.
neutral
If two _____________ objects are rubbed together, each can become charged.
neutral
There are several ways to charge a ____________ object.
neutral
The type of charge carried by an electroscope can be determined by ___________________ when a rod of known charge is brought close to the knob.
observing the leaves
The type of charge carried by an electroscope can be determined by ___________________________.
observing the leaves when a rod of known charge is brought close to the knob
Electric field lines are _______________________ electric fields. They are not the electric field itself.
only a way of representing
The leaves will fall slightly if the electroscope's charge is _________________ that of the rod.
opposite
There are two kinds of electric charges: _______________________.
positive and negative
The direction of an electric field is the direction of the force on a ___________________.
positive test charge
An atom missing electrons has an overall positive charge, and consequently, any matter made of these electron-deficient atoms is ____________ charged.
positively
The test charge exerts forces back on the charges that produce the electric field. It is important that these forces do not __________________ the charges that you are trying to measure, thereby affecting the electric field that you are trying to map.
redistribute
Like charges __________; opposite charges ____________.
repel --- attract
Like electric charges _________, and unlike electric charges __________.
repel --- attract
The leaves will spread farther apart if the rod and the electroscope have the _____________ charge.
same
The charge on a _______________ is −1.60×10^19 C. The magnitude of the charge of an electron is called the ____________________.
single electron --- elementary charge
The charge on a___________________^ is +1.60×10−19 C. That is, the magnitude of the charge of a proton is _________ to the magnitude of the charge on an electron.
single proton --- equal
the leaves hang loosely and are enclosed to eliminate __________________. The electroscope is _______________.
stray air currents --- neutral
The direction of the electric field at any point is the _______________ drawn to a field line at that point.
tangent
Two objects with ________ charges always attract each other.
unlike
Coulomb's law is ___________ only for point charges or uniform spherical charge distributions.
valid