Unit 2 test Gary

Alternating current (AC)

electrons first move in one direction and then
reverse and move in the opposite direction; oscillation of electricity in both
directions within a conductor

Direct current (DC)

flow of electricity in only one direction (unidirectional)
within a conductor

Ohms law

states that voltage in a circuit is equal to the current times resistance; V = IR

Power

Rate at which work is done

Resistance

the amount of opposition to the current in the circuit; measured in ohms

Watts (W)

Electrical power is measured in watts; One Watt is equal to one ampere of current that flows through and electric potential of one volt

Resistor

Inhibits flow of electrons

Battery

Provides electric potential

Capacitor / Condenser

Temporarily stores electric charge

Ammeter

Measures electric current

Voltmeter

Measures electric potential

Switch

turns circuit on or off by providing infinite resistance

Transformer

increases or decreases voltage by fixed amount (ac only)

Rheostat / Potentiometer

Acts as a variable resistor

Diode

Allows electrons to flow in only one direction

List ways of modifying the wire
to increase resistance:

Reduce its diameter
Increase its length
Inserting circuit elements (resistor)

Electron flow

within a circuit is from negative to positive poles (e- flow from
highest to lowest concentration)

Conventional electric

current flows from positive to negative poles (exact
opposites)

Direction of Travel

AC verses DC
(four-diode rectification circuit: one-way street)

Current

# of e- flowing in circuit per second
Quantity measured in Amps
(mA station)

Potential difference

Strength or Force of e- flowing in circuit
Emf, electric potential, or voltage
(kVp station)

Resistance (Opposition)

Opposition to current (Ohms) Ω
According to Ohms Law, if we increase the resistance our current decreases
(filament circuit)

Ability to conduct electrons

Conductivity of materials
(Conductors, Insulators, etc.)
Most metals are good conductors

Length of conductor (wire)

increase length of wire = increase resistance; directncrease length of wire = increase resistance; direct

Cross-sectional diameter of
wire

Increase diameter = decrease resistance; inverse

Temperature

Increase temperature = increase resistance; direct
(more electron collisions)

R =

Resistance ( Ohms )

Formula for total current in series circuit

I total = I (1) = 1 (2) = 1 (3)

I =

Current ( amps )

V =

Potential difference ( Volts )

Formula for total current in parallel circuit

I ( total ) = I ( 1 ) + I ( 2 ) + I ( 3 )

Formula for resistance in series circuit

R ( total ) = R ( 1 ) + R ( 2 ) + R ( 3 )

Formula for potential difference ( Volts ) in series circuit

V ( total ) = V ( 1 ) + V (2) + V (3)

Series Circuit

All circuit elements are connected in a line along the same conductor linking them one after another

Ex. Christmas lights in a series circuit, one goes out, the entire string goes out

Series Circuit shortcut

R +

I =

V +

Parallel Circuit

Contains elements that bridge conductors rather than lie in a line along a conductor
• Each component is given an individual branch
• Ex. Christmas lights, one light goes out, the rest will stay on, has two wires in each lamp

Formula for resistance in Parallel Circuit

1/R (total) = 1/(R1) + 1/(R2) + 1/(R3) don’t forget to flip at end .

Formula for potential difference in parallel circuit

V (total) = V (1) = V(2) = V(3)

Parallel Circuit Shortcut

I +

V =

1/R +

Ohms law Formula

V = IR

V = Potential Difference ( Volts )

I = current ( Amperage / Amps )

R = Resistance ( Ohms )

Power formula

P = IV

P = Power ( watts )

I = Current ( amps )

V = ( Potential difference )

Power ( Heat ) loss formula

P = I ² R

Power loss = Current² x resistance

Electrical current

the movement of electrons along a conductor (wire) or pathway (electrical circuit); measured in amperes

Electrodynamics

electrical charges in motion; electricity

Electrostatics

The study of the distribution of fixed (stationary) charges, or electrons that are at rest; static electricity

Electromotive force (emf)

the force or strength of electron flow; also know as potential difference or electric potential; voltage

Electrification

describes the process of electron charges being added to or subtracted from an object through friction, contact or induction

Conductor

A material that allows electrons to flow freely

Coulomb

the SI Unit of electric charge; 1 C = 6.24 × 10^18 electron charges

Induction

The process of electrical fields acting on one another without contact; utilized in operation of electronic devices

Insulator

A material that inhibits electron flow

3 Methods of
Electrification

Friction , Induction , and Contact

Factors Impeding flow of electron

ability to conduct electrons

Length of conductor ( wire )

Cross-sectional diameter of
wire

Temperature

Friction

“Rubbed”, Cold & Low Humidity
Balloon against sweater, walking across carpet

contact

“touch”, simple equalization of charges
Touching a metal doorknob or person
Static discharge on a radiograph

Induction

Interaction of electric fields without contact
Electronic devices: motors, transformers, solenoids
Induction motor in vacuum x-ray tube
Tell gross story!

fundamental unit of electric charge is

the coulomb (C)
1 Coulomb = 6.24 x 10^18 electron charges

Five Laws of Electrostatics

Repulsion - Attraction

Distribution

Concentration

Movement

Coulomb’s Law & Inverse Square

Repulsion-Attraction

Opposites attract, like charges repel
Ex. filament & focusing cup

Distribution

Charges reside on the external surfaces of conductors
and are distributed equally throughout nonconductors
Ex. Copper wire verses cloud

Concentration

The greatest concentration of charge (e-) will be on
the surfaces where the curvature is the sharpest
Ex. focusing cup & why tubes are highly polishe

Movement

Only negative charges move along solid conductors
Ex. electrons flowing in circuit

Coulomb’s Law

Measures the magnitude of electrostatic force

Inverse Square

Effect distance had on force of attraction or repulsion

Coulomb’s Law formula

F = k x Q (1) x Q (2) / D²

Q = electrostatic charges in Coulombs (C)

d = distance

K = (9 x 10^9 Nm^2/C^2) constant of proportionality

K for Coulombs Law

(9 x 10^9 Nm^2/C^2) constant of proportionality

Coulomb law ex problem

Suppose that two-point charges, with a charge of + 4.00 Coulombs and the other at 2.00 Coulombs are separated by a distance of 3.00 meters.
Determine the magnitude of the electrical force of repulsion between them.

8 × 10^9 N

Inverse Square Law

I (1) / 1 (2) = D² (2) / D² (1)

I (1) = Old intensity

I (2) = New intensity

D² (2) = New distance squares

D² (1) = Old distance squares

Inverse square law problem ex.

If an object has a charge of 2 coulombs at 5 mm,
what will be the charge at 12 mm?

.347 C

Electric Potential

-The force or strength in which electrons flow
-It is a function of the difference between the number of electrons on either end of the circuit
-There is an excess of electrons at one end of the circuit, and the deficiency of electrons at the other end

Electric Potential aka

potential difference, electromotive force (emf), voltage or strength

ampere (A)

Electric current is measured in a unit called the ——

—-measures the number of electrons flowing in the circuit per unit of time

Conductivity

a measure of the ability of a given substance to
conduct electric current (allowing free flow of electrons)

Conductor

Material - Copper, Aluminum, Gold

Characteristics - Allows the free flow of electrons
Obeys Ohm’s Law
Requires an electric potential or voltage

Insulator

Material - Rubber, Plastic, Glass, Clay

Characteristics - Resists or does not permit
electron flow
Necessary with high voltages

Semiconductor

Material - Silicon , Germanium

Characteristics - Can be conductive or can be resistive
Basis for computers

Superconductor

Material - Niobium, Titanium

Characteristics - No resistance to electron
flow
No electric potential required

Amplitude

The intensity of a wave defined by its maximal height or ½ the range from crest to valley; wave height

Electromagnetic energy

a form of energy resulting in electric and
magnetic disturbances in space

Frequency

The number of cycles or wavelengths passing a given point per unit of time; expressed in hertz or cycles per second

Photon

The smallest amount of any type of electromagnetic radiation; a bundle of energy called a quantum

Sine waves

variation in the movement of photons in electrical and magnetic fields or waves of electromagnetic radiation

Velocity

The rate of change of an object’s position over time; speed or how fast an object is moving

Wavelength

The distance between any two successive points on awave; from crest to crest or from trough to trough

X-ray Imaging: Energy range

10,000 eV to 100,000 eV

X-ray Imaging: Frequency

10^18 to 10^20 Hz

X-ray Imaging: Wavelength

10^-10 to 10^-12 meters

Photon Properties

1. The have no mass or identifiable form

2. Possess both electric and magnetic properties
    Travel in waves along a straight path (in a sinusoidal fashion)

3. Requires no medium; therefore, can travel in a vacuum
    E.g., space

Characteristics of Sine waves

1. Velocity
2. Amplitude
3. Frequency
4. Wavelength

All Electromagnetic radiation travels at the speed of
light or not at all. True or False ?

True

The wave amplitude is not related to wavelength or
frequency. True or false ?

True

Frequency and wavelength are____

inversely proportional

Energy and frequency are_____

directly proportional

Electromagnetic Wave Equation

Constant = Frequency x Wavelength

Constant for Electromagnetic Wave Equation

3.0 × 10 ^8 m/s

Electromagnetic Wave Equation ex. problem

EM wave has a frequency of 2.4 x 10^9 Hz. What is its wavelength expressed in meters?

1.25x10^-1m

Plank’s Constant Formula

E = HF

Plank’s Constant ex. prob

What is the frequency of a 55 keV x-ray?

1.33 x 10^19 Hz OR

How much energy does an x-ray possess if its
frequency is 1.2 x 10^-7 Hz?

7.96 x 10^-41 Joules

Energy and Matter Formula

E = MC²

Energy and Matter ex. formula

What is the mass equivalent of a 23.6 keV x-ray?

4.2 × 10^-32 kg OR

What is the energy equivalent of a mass of 1.2 x 10^-10 kg ?

E = 1.08 x 10^7 J