psci chapter 6 electricity
electrostatic charge 141
"electric charges on objects result from the gain or loss of electrons" (static electricity) : -electrons can be moved from atom to atom to create ions. They can also be moved from one object to another by friction. Since electrons are negatively charged, an object that requires an excess of electrons by another body results in deficiency of electrons, which results in a positively charged object. Because the electric charge is confined to an object and is not moving, it is called an electrostatic charge. ex: static electricity is accumulated electric charge at rest, that is, one that is not moving. When you comb your hair with a hard rubber comb, the comb becomes negatively charged because electrons are transferred 'from' your hair to the comb. Your hair becomes positively charged with a charge equal in magnitude to the charge gained by the comb. Both the negative charge on the comb from an excess of electrons and the positive charge on your hair from a deficiency of electrons are charges that are momentarily at rest, so they are electrostatic charges.
electromagnetic induction 161 electromagnetic inductions depends on...
-If a loop of wire is moved in a magnetic field, or if the magnetic field is changed, a voltage is induced in the wire. The voltage is called 'induced voltage' and the resulting current in the wire is called an 'induced current.'The overall interaction is called an electromagnetic induction. -the relative motion of the magnetic field and the coil f wire. It does not matter which moves or changes, but one must move or change relative to the other for it to occur.
electromagnetic induction occurs when a coil of wire cuts across magnetic field lines. Which of the following increases the voltage produced?
... 161 WROTE OUT
coulomb 143
1 coulomb (C) = charge carried by 6.24 x 10^18 electrons Charge of one electron = 1.00/ 6.24 x 10^18 electrons/C = 1.60 x 10^-19 C/electron q = quantity of charge in coulombs A rubber balloon has become negatively charged from being rubbed with a wool cloth. The charge is measured as 1.00 x 10^14 C. How many excess electrons are on the balloon? Given: q = 1.00 x 10^-14 C e = 1.60 x 10^-19 C/electron Find: n = number of electrons Equation: q = n e n = q/e Solution: n = (1.00 x 10^-14 C)/(1.60 x 10^-19 C/elec.) = 0.625 x 10(^-14-^(-19)) = 0.625 x 10^5 = 6.25 x 10^4 electrons
an object can become electrostatically charged by
1- friction, which transfers electrons from one object to another 2- contact with another charged body, which results in the transfer of electrons 3- induction (produces a charge by redistribution of charges in material)
4 factors that influence the resistance of an electrical conductor
1- the length of the conductor 2- the cross sectional area of the conductor 3- material the conductor is made of 4- temperature of conductor
Electromagnetic induction occurs when the loop of wire moves across magnetic field lines or when magnetic field lines moves across the loop. The magnitude of the induced voltage is proportional to:
1- the number of wire loops passing through the magnetic field lines 2- the strength of the magnetic field 3- the rate at which magnetic field lines pass through the wire.
amp
147
parallel circuit
166
the law that predicts the behavior of electrostatic forces acting through space is
Coulomb's law
electric current can be direct current or alternating current. what are they?
DC—direct current charges flow in one direction AC—alternating current charges alternate in direction
electric field
Electric field lines show the direction a positive test charge would move if placed in any location in the vicinity of a charged object. The closer the test charge is to the object, the greater the force of attraction or repulsion. A positive test charge would be influenced by both objects: -A positive test charge would move away from any other positive charge. -A positive test charge would move toward any negative charge.
ohm's law
The current (I) in amperes (amps) is directly proportional to the potential difference in volts (V) and inversely proportional to the resistance (R) in ohms (Ω) in the circuit. I = V/R V = IR
electrical conductors
The electrostatic charge is produced by friction between two surfaces and will remain until the electrons can move away because of their mutual repulsion. This usually happens when you reach for a metal doorknob and the electron movement creates a spark. Materials like metal are good 'electrical conductors' because they have electrons that are free to move around throughout the metal. Plastic and wood materials are not good conductors because they do not have electrons that are free to move throughout the material. (called electrical nonconductors or insulators- rubbers, glass, plastics bc they hold tightly to their electrons= good insulators)
an electric field describes the condition of space around
a charged particle
to be operational, a complete electric circuit must contain a source of energy, a device that does work, and
a conductor from the source to the working device and another conductor back to the source
short circuit 164
a current always takes the path of least resistance -occurs when some low resistance connection or "short cut" is accidentally established between two points in an electric circuit
a current carrying wire has a magnetic field around it because
a moving charge produces a magnetic field of its own
a) A neutral atom has ___ because ___ b) removing an electron produces a ___ c) the addition of an electron produces a ___
a) no net charge, because the numbers of electrons and protons are balanced b) net positive charge c) negative charge and negative ion
in which of the following currents is there no electron movement from one end to a conducting wire to the other end?
alternating current: moves electrons alternately one way, then the other way. Since electrons are moving back and forth, there is no electrical drift along a conductor
the rate at which electric current flows through a circuit us measured in units of
amp
the strength of a magnetic field around a current carrying wire varies directly with the
amperage of the current
an electromagnet uses___ to produce a magnetic field
an electric current
Glass is an example of
an electrical insulator
the speaker in a stereo system works by the action of
an electromagnet pushing and pulling on a permanent magnet
a piece of iron can be magnetized or unmagnetized. this is explained by the idea that
atoms of iron are grouped into tiny magnetic domains that may orient themselves in a particular direction or in a random direction
you are using which description of a current if you consider a current to be positive charges that flow from the positive to a negative terminal of a battery?
conventional current
the unit of electric charge is the
coulomb (the size of an electric charge is identified with the number of electrons that have been transferred to or away from an object. The coulomb measures the quantity of such charge)
_____ variable is inversely proportional to the resistance
cross sectional area of conductor
what type of electric current is produced by fuel cells and solar cells?
dc
a material that has electrons that are free to move throughout the material is a
electrical conductor
a solar cell produces
electricity directly
electromagnetic induction takes place because
electrons have their own magnetic field, which interacts with an externally applied magnetic field
An electrical non conductor is most likely to acquire a ____ charge
electrostatic charge
when an object acquires a negative charge, it actually
gains mass
electric circuit 147
has a voltage source (such as a generator or battery) that maintains the electrical potential, some device (such as a lamp or motor) where work is done by the potential, and continuous pathways for the current to follow. his slide: -any closed path along which electrons can flow -for continuous flow — no gaps (such as an open electric switch)
a positive and a negative charge are initially 2 cm apart. What happens to the force on each as they are moved closer and closer together? the force WHY??
increases while moving
a lodestone is a natural magnet that attracts
iron, cobalt, nickel
electric current148
is the flow of electric charge -in metal — conduction electrons -in fluids — positive and negative ions • measured in amperes One ampere is the rate of flow of 1 coulomb of charge per second or 6.25 billion billion electrons per second! So current (I) in amperes (amps or A) is the rate of charge movement per unit time I = q/t
a current carrying wire always has a____ with _____ around the length of the wire
magnetic field closed concentric field lines
earths magnetic field has undergone...
many reversals in polarity
magnetism is produced by
moving charges
series circuit
negative terminal of one cell connected to the positive terminal of another cell. The total voltage produced this way is equal to the sum of the single cell voltages. from summary: has resistances connected one after the other so the same current flows through each resistance one after the other.
the north pole of a suspended or floating bar magnet currently points directly toward earths
north magnetic pole
the elctrical resistance of a conductor is measured in units of
ohm
electrical resistance 150
opposing or reducing a current in materials
in which type of circuit would you expect the same voltage with an increased current as more and more resistances are added to the circuit?
parallel circuit -A branched pathway is formed for the flow of electrons -A break in any path doesn't interrupt flow in other paths -A device in each branch operates independently of the others -Total current in the branches add
if you multiply volts by amps, the answer will be in units of
power
when a loop of wire cuts across magnetic field lines or when magnetic field lines move across a loop of wire, electrons are
pushed toward one end of the loop
the units: amp and watt are measures of
rates
electric power companies step up the voltage of generated power for transmission across the country because higher voltage
reduces the current, which lowers the energy lost to resistance
like charges ____. Unlike charges ____ electrons have a ___ charge and protons have a ____
repel + + attract +- negative positive
reverse the direction of a current in a wire, and the magnetic field around the wire will have a ____direction
reversed north pole
a parallel circuit has____ for the current to flow through
separate pathways
in which type of circuit would you expect a reduction of the available voltage as more and more resistances are added to the circuit?
series circuit -A single-pathway circuit for electron flow -A break anywhere in the path results in an open circuit; electron flow ceases -Total resistance adds, more devices, less current (I = V/R)
an electric meter measures the
strength go a magnetic field
silver is not considered to have ______ properties?
strong magnetic
a permanent magnet has magnetic properties because
the magnetic domains are aligned
electrostatic charge results from
transfer or redistribution of electrons
a ____ changes the voltage of an alternating current
transformer
the operation of car stereo speakers, telephone, relay circuit depends on the interaction between
two magnetic fields
the current in the secondary coil of a transformer is produced by a
varying magnetic field
in an electric current, the electrons are moving at a __rate
very slow rate
the electrical potential difference between two points in a circuit is measured in units of
volt
a step up transformer steps up the
voltage
according to Ohm's law, what must be greater to maintain the same current in a conductor with more resistance?
voltage
units of joules per second are a measure called a
watt
earths magnetic field is believed to originate
with electric currents that are somehow generated in earths core
a kilowatt-hour is a unit of
work
