Test 2 Flashcards
The four types of electrical material are:
Conductors, insulators, semiconductors, and superconductors.
Which material is not a conductor? Copper penny Silver dollar Wooden stick Saltwater
Wooden stick
Which of these materials is not an insulator? Copper wire Plastic spoon Rubber knife Wooden ruler
Copper wire
The force fields created by a magnet are called
Lines of flux
A(n) —– will conduct an electric current with no resistance.
Superconductor
The three methods of generating static charges are:
Friction, induction, and contact.
The unit of electric charge is the
Coulomb
What is the smallest unit of electric charge?
Electron
The force between two positive charges is
Repulsion
The force between a positive and a negative charge is
Attraction
The ability with which a material can be magnetized is its
permeability
Materials that are weakly repelled by all magnetic fields are
diamagnetic
The electrostatic law states that
an electron will repel an electron.
------- is a very good conductor. Rubber Copper Glass Wood
Copper
The SI units of magnetism are the
weber and tesla
Which of these materials is not ferromagnetic? Iron Wood Nickel Cobalt
Wood
Which of these materials is ferromagnetic? Wood Glass Cobalt Plastic spoon
Cobalt
A ferromagnetic material is
strongly influenced by magnetic fields.
The ability of a magnet to resist demagnetization is called
retentivity
Which statement is not one of the laws of magnetism?
- like poles repel
- unlike poles attract
- the force between magnets increases with the square of the distance between them.
- the force between magnets decreases with the square of the distance between them.
The force between magnets increases with the square of the distance between them.
What is the main function of an x-ray system?
To convert electric energy into electromagnetic energy.
Describe “ground” or “neutral” potential.
Earth is the neutral or ground potential
This is because it has + and – charges equally distributed
It is always available to accept electric charges
The smallest unit of electric charges are:
Electron (negative)
Proton (positive)
The proton & electron each have one unit of charge
Electric charges deal with
the negative electric charges associated with the electron.
Unit of electric charge is
the Coulomb (C) (1C = 6.3 x 1018 electron charges)
Electrostatics or Static Electricity is
the study of stationary electric charges or electrons that are at rest
If an object has too few or too many electrons then
it becomes electrified.
An abundance of electrons causes
a shock.
Electrons jump the gap& form
a static discharge
Electrification is created by
Contact (touching metal doorknob)
Friction (rubbing shoes against carpet)
Induction (clouds in thunderstorm)
Electrification is due to
the movement of negative electric charges
Static electricity is:
the result of electrons being removed from the outer shell of atoms and the object that the atom is a part of becoming electrified.
Static discharge releases excess energy in the form of _______ and forms a/n _____ on film. This can be controlled with:
light photons/image/humidifiers.
True or false? Only positive electric charges move.
False. Positive electric charges do not move. It is always the electrons that move.
Eletrostatic laws
Unlike charges attract; like charges repel Coulomb's law Distribution Concentration Movement
Electrostatic force is:
the force of attraction between unlike charges or repulsion between like charges due to the electric field.
Coulomb’s law
The electrostatic force is directly proportional to the product of the electrostatic charges and inversely proportional to the square of the distance between them.
Distribution:
Electric charge (excess electrons) distribution is uniform throughout or on the surface.
Concentration
Electric charge of a conductor is concentrated along the sharpest curvature of the surface.
Movement:
Only negative charges move along solid conductors.
What are the three ways objects can be electrified?
Through friction, contact or induction.
Electrification through friction:
Occurs when objects are rubbed against one another, due to differences in the # of electrons available on each, electrons travel from one object to the other. Ideal conditions are low temps and low humidity.
Electrification through Contact:
occurs when two objects touch, permitting electrons to move from one object to the other. Simply the equalization of charges since both objects will have similar charges after the contact.
Electrification through induction:
when strong and weak charged objects come close to on another, the electrical fields will begin to act on one another before contact occurs. Charges migrate to one ind of an object in anticipation of contact. Induction is the process of electrical fields acting on one another without contact.
Three main factors that make up an electrical circuit:
Potential difference (voltage)
Current (amperage)
Resistance (Ohms)
If like electric charges are positioned close to each other, they have electric potential energy. Why?
When they repel one another, they are doing work. Energy is the ability to do work.
Potential difference is the best term to describe the force or strength of electron flow. Why?
The force with which the electrons travel in a wire is the difference between the number of electrons in excess at one end of the circuit and the lack of electrons at the other end. The attempt to balance these is the cause of the force of electron movement.
Potential difference:
the amount of work used in moving a charge from one point to another.
The unit of electric potential is
the volt. (V)
Electromotive force (emf) is also known as
potential difference, which is the prime force causing electrical devices to convert electrical energy to mechanical form. Potential difference = electromotive force = voltage.
The definition of electromotive force is:
the quantity of work or energy needed to move a unit of electric charge through the circuit. The difference in potential between terminals of a better is considered emf.
Volt =
joule/Coulomb (J/C)
The quantity or number of electrons flowing is referred to as
current
Electric current is simply:
the amount of electric charge flowing per second.
The unit of current is
the ampere (A). The symbol = I (for intensity)
The ampere is the —– at which electrons move through a conductor.
rate
1 ampere =
1 Coulomb/1 second. (A coulomb is a unit of electric charge)
milliAmperage effects how ——- the image is.
dark
Kilovoltage effects the ——- of the image.
contrast.
The direction of electric current is ——- compared to electron flow.
opposite
Electric current travels in which direction?
Positive to negative
Electron flow travels from:
negative to positive.
What two ways can electrons travel?
they can all move in the same direction: Direct current (DC) or they can move first in one direction and then reverse and move in the opposite direction: alternating current (AC)
Electricity is supplied to equipment as either ___or____
AC or DC
DC is provided by 2 wires connecting the equipment to a power source which maintains ______
a constant potential difference between the two wires. Example: chemical batteries produce DC
DC wavelength looks like:
completely horizontal. It goes in one direction and does not go back and forth between positive and negative.
AC wavelength looks like:
a sine wave….goes back and forth between a positive direction and negative direction.
AC cycle (flow) measures:
60 times a second or 60 Hz
The advantage of transforming from AC to DC:
Amplitude can be increased or decreased using devices called transformers. (AC can have voltage changed, DC cannot.)
Semiconductors:
under some conditions behave as in insulator and in other conditions behaves as a conductor.
As the temperature decreases, resistance:
decreases. Resistance is directly proportional to temperature.
Superconductivity
the property of some materials to exhibit NO resistance below a critical temperature. They conduct electrons with zero resistance when they are cooled to very low temps.
Electric circuit:
when we control the resistance and the conductor is made into a closed path. (Current flows only when a path is closed.)
The amount of opposition to the current in the circuit is called
resistance
Unit of resistance is
the ohm
And electrical circuit is a pathway that:
permits electrons to move in a complete circle from their source through resisting electrical devices and back to the source.
In order for electrons to flow through a circuit, there must be:
an excess charge at one ind and a comparative deficiency at the other.
Even through current flows only when you have a closed circuit, the potential difference still exists, so:
if a very high voyage exists, it is extremely dangerous because YOU can provide a path for electricity.
Four factors that effect the flow of electrons which can increase or decrease resistance are:
Conductivity
Length of the conductor
the diameter of the conductor
Temperature
Ohm’s law
The voltage across the total circuit or any portion of the circuit is equal to the current times the resistance. V=IR
The two types of electrical circuits are
Series or parallel
Series circuit
connected in a line along the same conductor.
Rules for series circuit
The total resistance is equal to the sum of the individual resistance. The current through each circuit elements is the same and is equal to the total circuit current. The sum of the voltages across each circuit element is equal to the total circuit voltage.
Rtotal= R1+R2+R3
Itotal= I1 = I2 = I3
Vtotal= V1 + V2 + V3
In a series circuit, the current always:
stays the same. So as resistance increases, the voltage increases. (V=IR)
Parallel circuit contains:
elements that are connected at their end rather than a lie in a line along a conductor. The current is divided among several branches or paths flowing simultaneously.
Rules for Parallel circuits
The sum of the currents through each circuit element is equal to the total circuit current (Itotal = I1 + I2 + I3). The voltage across each circuit element is the same an dis equal to the total circuit voltage. (Vtotal = V1 = V2 =V3). The total resistance is the inverse of the sum of the reciprocals of each individual resistance. (1/Rtotal = 1/R1 + 1/R2 + 1/R3).
While the voltage remains the same in a parallel circuit, the largest amount of current will flow…
…through the path with the least resistance.
Conductance is:
the reciprocal of resistance and is the flow of electrons.
Conductance is measured in:
Siemens
The addition of current-using devices to a series circuit causes:
the voltage to drop, reducing the potential difference to the other devices in the circuit.
Disadvantage to parallel circuits:
with the addition of resistances, the increasing amperage can short circuit the entire system, which could possibly start a fire. To prevent this a circuit breaker or fuse is placed in the line.
Electric power is measured in:
watts (W)
The watt is defined as
1 ampere flowing through 1 volt per second.
Power=
amperage (or current) times voltage (P=IV)
Ammeter
When a meter is connected in a series circuit, it measures current in amperes.
Ammeters measure:
The quantity of electric charge flowing per second.
When a meter is connected in a parallel circuit, it measures:
potential difference in volts.
A voltmeter measures:
the pressure in the circuit where there is high resistance.
The potential difference (voltage) in a parallel circuit is often referred to as
voltage drop.
Any charged particle in motion creates
a magnetic field.
Magnetic fields are created by:
electron spin.
The magnetic field of a charged particle is _____ to the motion of that particle
perpendicular.
The small magnet created by electron orbit is called….
…a magnetic dipole. An accumulation of these dipoles create a magnetic domain. When all the magnetic domains in an object are aligned it acts like a magnet.
When acts upon by an external magnetic field, the randomly oriented dipoles…
…align with the magnetic field. This is what happens when easily magnetized material is made in to a permanent magnet.
Fields that have both a north and a south pole are called
bipolar or dipolar.
Lines of force always flow:
from north to south outside a magnet and from south to north inside a magnet.
The lines of force never:
intersect.
The lines of a magnetic field are always
closed loops.
Force fields created by a magnet are also called
lines of force or lines of flux.
The stronger the magnetic field the greater the number of:
lines of flux or the greater the flux density.
In a wire carrying a current, the magnetic field closest to the wire:
is the strongest.
Flux density is determined both by:
(magnetic) field strength and by the area in which the ones of flux are located. Magnetic flux = field strength/area.
The two units used to measure the strength of magnetic fields are:
The Weber (Wb) and the Tesla (T)
Three principal types of magnets:
Naturally occurring
Artificially induced permanent
Electromagnets
Natural magnets are created when:
iron oxide remains in the earth’s magnetic field for ages, slowly orientating the magnetic dipoles in the same direction.
The best example of a natural magnet is
the earth itself.
Artificially produced magnets
manufactured from a shell alloy called alnico (aluminum, nickel and cobalt.)
The magnetic property of a magnet can be destroyed by
heating or hitting with a hammer
