Chapter 23: Electric Current Flashcards
When there is a potential (voltage) difference charge flows from
One end to the other analogous to water flowing from higher pressure to lower pressure
Flow of charges occur will both potentials and pressures are
Equal
To obtain a continuous flow of charge in a conductor: A certain arrangement is required to
Maintain a potential (voltage) difference while the charge flows from one end to another a battery is an example of such a device
A continous flow is possible if the difference in water pressure is
Maintained with the use of a pump
A pump maintains the difference in
Water level and hence the difference in water pressures
Electric current flow of charged particles in
Metal wires
Conduction electrons are charge carriers that
Freely move throughout an underlying fixed atomic lattice
Protons are bound within the nuclei of
Lattice atoms and do not flow
Electron current is a rate of electric flow measured in
Ampere (1 coulomb per second)
Speed of electrons (drift speed) through a wire is slow because of
Continuous bumping of electrons in wire
Voltage sources charges flow only when they are
“Pushed” or “driven”
A continuous current needs a pumping device to provide a difference in
Electrical potential like a voltage
Electrons in conductor flow from
Lower potential (-) to higher potential (+) inside a conducting material
A battery or generator can maintain a
Steady flow of charge
Batteries and electric generators do work to
Pull negative charges away from positive ones
Work is done by
Chemical disintegration of zinc or lead in an acid
Energy stored in chemical bonds within the battery is converted to
Electric potential energy
Current in a circuit depends on
Voltage and electrical resistance are measured in ohms
Resistor
1) Circuit elements that regulate current inside electrical devices
2) Circuit symbol for resistance in an electric circuit
Factors affecting electrical resistance
1) Inversely proportional to cross-sectional area
2) Directly proportional to length
3) Temperature
4) Material (resitively)
Inversely proportional to cross-sectional area
Thin wires, more resistance than thick wire
Directly proportional to length doubling the
Length and the resistance
Material (resitively): like rubber is much more
Resistance than copper of the same size
Ohm’s Law
The current is a circuit varies in direct proportion to the potential difference, or voltage, and inversely with the resistance
For a constant resistance, current will be
Twice as much for twice the voltage
For twice the resistance and twice the voltage, current will be
Unchanged
When you double the voltage in a simple electric circuit, you double the
Current
Electric shock: Damanging effects of shock result from
Current passing through the body
Electric potential differences between
One part of your body and another part depends on body condition and resistance which can range from (100 ohms to 500,000 ohms)
Does the bird feel a shock?
No, each claw is at the same voltage
Cannot feel the current produced by what volt?
12 to 24 volts just barely tingles
Direct current (dc)
1) Flow in one direction only
2) Electrons always move from the negative terminal toward the positive terminal
Alternating current (ac)
1) Current alternatively flows in one direction and then in the opposite direction repeating peiodically
2) This is accomplished by alternating the polarity of voltage at the generator or other voltage source
Household current is AC, current in a battery operated device such as
A laptop is DC
AC to DC conversion uses a
Diode: an electronic device that acts as a one-way valve to allow current flow in one direction only
Diode circuit symbol: As the symbol suggests, current flows in
The direction of the arrow but not in the reverse direction
When we flip the light switch on a wall and the circuit, an electric field is
Established inside the conductor
The electrons continues their random motions while simultaneously being
Nudged by the electric field
An E is established through the wires at nearly the
Speed of light
It is not the electrons that move at this speed, it is the
Electric field that can travel through a circuit at nearly the speed of light
If the voltage source is dc, like the battery, electric field lines are
Maintained in one direction in the conductor
Conduction electrons are accelerated by
The field in a direction parallel to the field lines
Before they gain appreciable speed, they “bump into” the anchored metallic ions in their paths and transfer some of their
Kinetic energy to them
Collision interrupt the motion of the electrons, so the speed at which they migrate along a wire is
Extremely low
This net flow of electrons is the
Drift velocity
At this rate, it would take about 3 hours for an electron to travel through
1 meter of wire
Conventional current
Flow of positive charges from high potential (+) to low potential (-)
Electron current
Flow of negative charges from low potential (-) to high potential (+)
Electric power
Rate at which electric energy is converted into another form is electric power
The brightness of incandescent lightbulbs can be judged by their
Power of a 100 W bulb glows brighter than a 60 W bulb
Incandescent bulbs dissipate most of their energy in the form of
Heat not light, so they are not energy efficient
Compact fluorescent lamps (CFLs) are a type of fluorescent lamp that fits into
A standard lightbulb socket
For the same wattage, CFLs emit much more
Light and much less heat than incandescent bulbs
Another light source even more long-lasting (and efficient) is
The light emitting diode (LED)
Between CFLs and LEDs, common use incandescent bulbs will soon be
History
An electric circuit is
A path involving wires and electric components through which electric current flows
A circuit must be complete (or closed) to allow current to
Flow continuously
Circuit elements are usually connected in either two ways
1) Series connection
2) Parallel connection
Series connection forms a
Single pathway for electron flow between the terminals of the battery, generator, or wall outlet
Parallel connection forms a
Branches each of which is a separate path for the flow of electrons
Electric current flows through a
Single pathway
For a resistor circuit, the total resistance is
The sum of individual resistance
Current is equal to the voltage supplied by the source divided by
The total resistance of the circuit
The sum of the voltages across the resistance of each individual device is equal to
The total voltages supplied by the source
The voltage drop across each device is proportional to
Its resistance
If one component fails current in the
Entire circuit ceases
Voltage is the
Same across each device
The amount of current in each branch is
Inversely proportional to the resistance of the branch
The total current in the circuit equals the
Sum of the currents in its parallel branches
As the number of parallel branches
Increases, the overall resistance of the circuit decreases
A break in one path does not
Interrupt the flow of charge in the other paths
When two identical lamps in a circuit are connected in parallel, the total resistance is
Less than the resistance of each lamp
Consider a lamp powered by a battery. Charges flow through both
The battery and the lamp
