Chapter 7 - Electrodynamics

Question 1

What is electricity?

Answer 1

the continuous flow of electrons along the surface of a conductor

Question 2

What is electrodynamics?

Answer 2

the study of flowing electrical current

Question 3

What is conductivity?

Answer 3

ability to transmit electrical current

Question 4

What is a material called when it allows electricity to pass through easily?

Answer 4

conductor

Question 5

What is a material called that is resistant to the flow of electricity?

Answer 5

insulator OR dielectric

Question 6

What is a material that will conduct electricity dependent on certain conditions called?

Answer 6

semiconductor

Question 7

What unit is defined as the rate of one coulomb per second?

Answer 7

AMPERE (measure of current)

Question 8

What is the rate of flow (speed) of electricity called?

Answer 8

CURRENT (measured in Amperes)

Question 9

How many electrons are in one mA?

Answer 9

6.3 x 10^15 electrons

Question 10

What is an electrical circuit?

Answer 10

a circle in which wires leave a battery or generator, pass through devices, and travel back to the battery or generator

Question 11

What are the three components of an electrical circuit?

Answer 11

• conductor
• source of EMF
• device to be operated

Question 12

What three changes in a conductor increase its electrical resistance?

Answer 12

• INCREASE LENGTH
• NARROW DIAMETER,
• USE A POOR CONDUCTING MATERIAL OR POOR CONSTRUCTION

Question 13

What are the two general types of electrical circuits?

Answer 13

• Series
• Parallel

Question 14

What does it mean to be wired in series?

Answer 14

Devices are connected in a row. If one device fails, they all fail.

Question 15

What does it mean to be wired in parallel?

Answer 15

Branches of wire split off of the original wire to connect each device. If one device branch fails, the rest stay connected.

Question 16

What are the 3 characteristics of electricity flowing in circuits?

Answer 16

1. current
2. resistance
3. EMF (electromotive force) or potential difference (voltage)

Question 17

What is the formula for Ohm’s Law? What does it measure?

Answer 17

V = IR
V = voltage
I = amperage
R = resistance

Question 18

What is the value of a volt? What does it measure?

Answer 18

• sufficient electrical force to push 1 ampere of current through 1 ohm of resistance
• electrical pressure, electromotive force, potential difference

Question 19

What is the unit of measure for resistance?

Answer 19

Ohm

Question 20

What is Power defined as?

Answer 20

the rate at which work is done (energy is spent)

Question 21

How does power relate to energy and time?

Answer 21

P = E / t
P = power
E = energy
t = time

Question 22

What is the unit of measure for electrical Power?

Answer 22

Watt

Question 23

How does power relate to voltage and amperage?

Answer 23

P = IV
P = Power
I = Intensity/Amperage
V = voltage

Question 24

What are the two general ways in which electricity can move in a wire or cable?

Answer 24

• DC (direct current)
• AC (alternating current)

Question 25

In which way do electrons flow in DC?

Answer 25

in one direction as a steady stream

Question 26

In which way do electrons flow in AC?

Answer 26

they oscillate back and forth

Question 27

What does Faraday’s Law state?

Answer 27

electrical current will flow through a conductor if it is placed in a CONSTANTLY CHANGING magnetic field

Question 28

AC current is required for any device that operates on the basis of electromagnetic _____.

Answer 28

INDUCTION

Question 29

What type of electrical current waveform is transmitted across an x-ray tube from cathode to anode?

Answer 29

RECTIFIED AC aka PULSED DC

Question 30

What does a generator create? from what?

Answer 30

AC electricity from a moving magnetic field (mechanical energy)

Question 31

What does a motor create? from what?

Answer 31

mechanical energy (movement) from AC electricity

Question 32

What are the two components of every motor?

Answer 32

• ROTOR
• STATOR

Question 33

What is a rotor?

Answer 33

the moving portion of a motor that rotates and usually spins an axle

Question 34

What is a stator?

Answer 34

the stationary part of a motor that consists of coiled wires surrounding the rotor that cause it to spin when current is passed through

Question 35

What is mutual induction?

Answer 35

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.

Question 36

What is an induction motor?

Answer 36

a motor in which both the rotor and stator are only coils of wire

Question 37

Which direction does induced current flow in relation to the original current?

Answer 37

the opposite direction (Lenz’s Law)

Question 38

What is a transformer?

Answer 38

a device that is able to change voltage or amperage of an electrical current

Question 39

What is the Transformer Law?

Answer 39

N2/N1 = V2/V1
N = number of turns on the coil
V = voltage
(directly proportional)

Question 40

What does a step-up transformer do in terms of voltage and amperage?

Answer 40

voltage goes up
amperage goes down

Question 41

What does a step-down transformer do in terms of voltage and amperage?

Answer 41

voltage goes down
amperage goes up

Question 42

What type of motor is used to rotate the x-ray tube anode?

Answer 42

INDUCTION MOTOR

Question 43

What type of transformer is used in the filament circuit of an x-ray machine so the filament can be heated?

Answer 43

STEP-DOWN
low voltage, high amperage creates friction/heat in the wire

Question 44

An autotransformer operates on the principle of:

Answer 44

SELF-INDUCTION