Ch.7 Electrodynamics Flashcards
(90 cards)
1
Q
The study of flowing electric current is what?
A
Electrodynamics
2
Q
If electric potential is applied to an object such as a copper wire, then these electric charges will move along the wire, this is known as?
A
Electric current or electricity
3
Q
What directions to electrons flow in an electric current?
A
negative to positive
4
Q
What direction does current flow in an electric current?
A
positive to negative
5
Q
What type of movement does electrons in the outermost shell portray in electric current?
A
they leap-frog from one atom to the next in sequence
6
Q
The rate of flow of electrons in known as?
A
current
7
Q
Current is measured as…
A
Electrons per second or Coulombs per second
8
Q
1 coulomb per second is what unit?
A
Ampere or amps
9
Q
Ampere or amps is abbreviated how?
A
A or I
10
Q
How many electrons sitting at rest represents 1 coulomb?
A
6.3x10^18
11
Q
What represents the number of electrons passing by a particular point in a wire each second as one Ampere?
A
6.3x10^18
12
Q
1 milliampere is how many amps?
A
1/1000th amps
6.3x10^15 electrons per second
13
Q
mAs represents what in regards to x-ray exposures?
A
the total number of electrons or total amount of electricity used for a particular x-ray exposure
14
Q
Electrical currents are what shape?
A
a circle
15
Q
In order to have a _____ conductors must pass from the voltage source (battery) through all devices and back to the source.
A
Circuit
16
Q
What happens if the circuit is broken at any point?
A
electricity stops flowing throughout the circuit
17
Q
What 3 components are required to have a circuit?
A
- a conductor
- a source of (EMF) electromotive force
- a device
18
Q
The wire is a source of electrons in a ____, not the battery.
A
Conductor
19
Q
A potential difference is needed to create the “pressure” that pushes electrons away from negative charge and pulls them toward positive charge in an _____.
A
electromotive force
20
Q
A ____ is operated, which uses up some of the energy from the electricity and thus acts as an electrical resistor in the circuit.
A
Device
21
Q
What are some conducting materials, they allow electricity to pass through them easily.
A
copper silver aluminum brass water
22
Q
What are some insulators, they resist the flow of electricity.
A
Rubber
Glass
Plastic
Dry wood
23
Q
These allow electricity to flow only under certain specific conditions.
A
Semi-conductors
24
Q
A conducting wire itself creates some resistance in what 3 ways?
A
- Long length of wire
- Narrow wire diameter
- Poor conducting material or poor construction
25
If voltage is increased in a conducting circuit the electrons will move slower or faster?
Faster
26
As electrons move faster more of them pass through any cross sectional area of the wire per second, and a larger ____ flows.
Current
27
The relationship between current-voltage-resistance for a conductor is expressed as_____ law
Ohm's Law
28
What is the formula for Ohm's Law?
V=IR
I=V/R
R=V/I
29
Current is measured in ____ abbreviated__.
Amperes, Amps-A or I
30
Potential difference or Electromotive force is measured in ___ and abbreviated __.
Volts- V or E
31
Resistance is measured in ___ and abbreviated __.
Ohm's- R or omega symbol
32
One volt provides sufficient force or pressure to push__ amperes of current through __ ohm or resistance.
1,1
33
What are the two general types of circuit layouts?
1. Series Circuit
| 2. Parallel Circuit
34
This circuit has all devices connected in a row one after another along the same wire and if one device burns out the entire circuit is broken and the current stops.
Series Circuit
35
This circuit has devices connected each in a separate branch of the wire which splits off from the original conductor. If one burns out the other devices are unaffected.
Parallel Circuit
36
_____ is defined as the rate at which work is done or rate at which electricity is used.
Power
37
Power is measured in what?
Watts
| 1 kilowatt= 1000 watts
38
1 watt is equal to __ amps flowing through an electric potential of 1 volt.
1
39
What is the power fomula?
P=IV...P is at the top of the formula triangle
I=P/V
V=P/I
40
What are the 2 types of electric wave form?
Direct Current
| Alternating Current
41
Electrons always flow in the same direction in a steady stream in ____Current.
Direct
42
Electrons oscillate back and forth is a ____ current.
Alternating
43
What wave forms are used by an X-ray tube in the production of x-rays?
```
Alternating Current (AC)
Direct Current (DC)
```
44
What is the actual speed of electrons in a DC current?
1 inch per hour
45
No matter how long a wire is, when a single electron is pushed into one end, electrons throughout the wire will shuffle one atom over and a single electron will exit the opposite end instantly, this represents which type of current wave form?
Direct Current
46
On a waveform graph, ____ current is shown as a period of electron acceleration when a switch is turned on, followed by steady flow and voltage, then a period of deceleration as the electrons come to a halt.
Direct Current
47
Waveform graphs plot ___ against ____.
Voltage of electricity against time
48
If DC current were to flow in the opposite direction the graph would show a curve ____ the baseline reaching a negative peak rather than a positive peak.
Under
49
For AC electricity the plotted waveform is identical to what?
A transverse wave
50
In the U.S AC devices work on __ Hertz of current and __ Hertz in Europe.
60, 50
51
Each cycle, negative and positive pulse, in an AC wave lasts for?
1/60th of a second
52
One pulse in an AC wave lasts how many seconds?
1/120th or .00833 seconds
53
A generator uses a moving magnet to induce electricity to flow by ______ Law.
Faraday's Law
54
An electric motor uses the constantly changing magnetic field around wires carrying AC current to cause a magnet to spin by ____ Law.
Oersted's Law
55
A generator converts ____ energy into _____ energy.
Mechanical into Electrical
56
An electric motor converts ____ energy into ____ energy or movement.
Electrical into mechanical
57
The magnitude of the induced current depends on what 4 things according to Faraday's Law.
1. Strength of the magnet
2. Velocity of magnet as it moves past the conductor
3. Angle of the conductor to the magnetic field
4. Number of turns in the conductor
58
AC waveform is typical of electric generators because they mechanically spin some type of magnet in ____ (cycles) top induce electricity to flow in a nearby coil of wire.
Circles
59
An electric current is induced in a circuit if some part of that circuit is in a ___ ___ ___.
Changing magnetic field
60
At the end of each pulse electrons technically stop and ____ directions, this happens so quickly though that they really are either accelerating and decelerating rather than stopping. It is at a constant speed.
reverses
61
What are the two parts to every motor?
The rotor and stator
62
This part of the motor spins (rotates) and is attached to wheels or some other device to turn. It spins when the motor is turned on.
The rotor
63
This part of the motor is stationary and contains coils of wire surrounding the rotor. Current is passed through the wires to cause the rotor to spin.
The stator
64
An ______ Motor is a motor that uses only coil of wire foor both the stator and the rotor. Due to the effects of electromagnetic induction, no actual magnet is needed.
Induction
65
With AC electricity, the constantly blooming and collapsing magnetic field around a wire will induce ____ ____ to flow in a nearby wire. The second wire now develops a magnetic field of its own, effectively becoming a ____.
electrical current, magnet
| - this is why induction motors need no actual bar magnet to run.
66
In Mutual Induction once the second wire becomes magnetized, the flow of electrons goes in which direction?
The opposite direction of the 1st wire
67
The induced current will flow the opposite direction from the original current, therefore, the induced magnetic field will lie opposite to the original, describes what law?
Lenz's Law
68
At all times the magnetic field around AC current is either growing or ______. Therefore current is constantly induced in the bottom wire.
collapsing
69
During DC electricity electrons only accelerate once? When is this?
When the switch is turned on
70
These change electric current and voltage to higher and lower values.
Transformers
71
Transformers alter the ____ or the ____ of electrical current.
voltage or amperage
72
If the iron bar of an electromagnet is extended and curved to form a closed loop, the magnetic lines of force cannot escape and become ______.
Concentrated
73
Which law states that change in voltage is directly proportional to the ratio of the number of turns of the secondary winding to the number of turns in the primary windings.
the Transformer Law
74
If the secondary coil has twice as many windings as the primary coil, then the voltage generated in the secondary coil will be _____.
Doubled
75
What is the voltage change across a transformer formula?
```
Vs/Vp=Ns/Np
Vs= secondary voltage
Vp= primary voltage
Ns= secondary turns
Np= primary turns
```
76
If the turns ratio is greater than 1, then it is a step-___ transformer where voltage increases and current decreasess.
up
77
If the turns ratio is less than 1 this is a step-___ transformer and voltage decreases and current increases.
down
78
Voltage and amperage are not conserved ____and can be leveraged ___ or ___ by transformers.
quantities, up, down
79
Amperage and voltage are _____ proportional to each other within a transformer.
inversely
80
In a transformer the change in amperage is ____ proportional to the turns ratio.
Inversely
81
These are used to change voltage in small increments.They work on the principle of self-induction.
Autotransformers
82
For autotransformers, the transformer ratio is the # of coils tapped off divided by the number of ____ available in the coil.
Turns
83
If there are 100 windings or turns, and the secondary taps are connected between 1 and 75 how much of the primary voltage will result?
75/100=3/4 primary voltage
84
Most x-ray machines have a step-___ transformer with a ratio of 1000:1
Up
85
At the x-ray machine console, the kVp controls are the settings for the _____ (leading up to a step-up transformer)
Autotransformer
86
This sets the secondary taps in multiples of 10.
kV Major
87
This sets the secondary taps in increments of 1 or 2.
kV minor
88
At the x-ray machine console, the mA controls are the setting for current fed into a step-____ transformer in a separate circuit.
down
89
The purpose of the step-down transformer(controlled by mA) is to provide high _____ current to the X-ray tube filament to heat it to extremely high temperatures. High friction is needed to do this.
amperage
90
High friction is produced when many trillions of _____ are crowded into the thin filament wire.
electrons
