Chapter 7 - Electrodynamics Flashcards
What is electricity?
the continuous flow of electrons along the surface of a conductor
What is electrodynamics?
the study of flowing electrical current
What is conductivity?
ability to transmit electrical current
What is a material called when it allows electricity to pass through easily?
conductor
What is a material called that is resistant to the flow of electricity?
insulator OR dielectric
What is a material that will conduct electricity dependent on certain conditions called?
semiconductor
What unit is defined as the rate of one coulomb per second?
AMPERE (measure of current)
What is the rate of flow (speed) of electricity called?
CURRENT (measured in Amperes)
How many electrons are in one mA?
6.3 x 10^15 electrons
What is an electrical circuit?
a circle in which wires leave a battery or generator, pass through devices, and travel back to the battery or generator
What are the three components of an electrical circuit?
- conductor
- source of EMF
- device to be operated
What three changes in a conductor increase its electrical resistance?
- INCREASE LENGTH
- NARROW DIAMETER,
- USE A POOR CONDUCTING MATERIAL OR POOR CONSTRUCTION
What are the two general types of electrical circuits?
- Series
- Parallel
What does it mean to be wired in series?
Devices are connected in a row. If one device fails, they all fail.
What does it mean to be wired in parallel?
Branches of wire split off of the original wire to connect each device. If one device branch fails, the rest stay connected.
What are the 3 characteristics of electricity flowing in circuits?
- current
- resistance
- EMF (electromotive force) or potential difference (voltage)
What is the formula for Ohm’s Law? What does it measure?
V = IR
V = voltage
I = amperage
R = resistance
What is the value of a volt? What does it measure?
- sufficient electrical force to push 1 ampere of current through 1 ohm of resistance
- electrical pressure, electromotive force, potential difference
What is the unit of measure for resistance?
Ohm
What is Power defined as?
the rate at which work is done (energy is spent)
How does power relate to energy and time?
P = E / t
P = power
E = energy
t = time
What is the unit of measure for electrical Power?
Watt
How does power relate to voltage and amperage?
P = IV
P = Power
I = Intensity/Amperage
V = voltage
What are the two general ways in which electricity can move in a wire or cable?
- DC (direct current)
- AC (alternating current)
In which way do electrons flow in DC?
in one direction as a steady stream
In which way do electrons flow in AC?
they oscillate back and forth
What does Faraday’s Law state?
electrical current will flow through a conductor if it is placed in a CONSTANTLY CHANGING magnetic field
AC current is required for any device that operates on the basis of electromagnetic _____.
INDUCTION
What type of electrical current waveform is transmitted across an x-ray tube from cathode to anode?
RECTIFIED AC aka PULSED DC
What does a generator create? from what?
AC electricity from a moving magnetic field (mechanical energy)
What does a motor create? from what?
mechanical energy (movement) from AC electricity
What are the two components of every motor?
- ROTOR
- STATOR
What is a rotor?
the moving portion of a motor that rotates and usually spins an axle
What is a stator?
the stationary part of a motor that consists of coiled wires surrounding the rotor that cause it to spin when current is passed through
What is mutual induction?
The magnetic field from one wire with current interacts with a nearby secondary wire and induces electrical current in it through the changing magnetic field.
What is an induction motor?
a motor in which both the rotor and stator are only coils of wire
Which direction does induced current flow in relation to the original current?
the opposite direction (Lenz’s Law)
What is a transformer?
a device that is able to change voltage or amperage of an electrical current
What is the Transformer Law?
N2/N1 = V2/V1
N = number of turns on the coil
V = voltage
(directly proportional)
What does a step-up transformer do in terms of voltage and amperage?
voltage goes up
amperage goes down
What does a step-down transformer do in terms of voltage and amperage?
voltage goes down
amperage goes up
What type of motor is used to rotate the x-ray tube anode?
INDUCTION MOTOR
What type of transformer is used in the filament circuit of an x-ray machine so the filament can be heated?
STEP-DOWN
low voltage, high amperage creates friction/heat in the wire
An autotransformer operates on the principle of:
SELF-INDUCTION
