chapter 3: Electricity

Electrons may not be associated with a nucleus at all, in which case they are called ____ electrons.

free

true or false:In either case, the positive charge of the proton and the negative charge of the electron are equal in strength.

true

True or false: Because electrons, with their negative charges,

are free to move between atomic orbital shells and even between atoms. electricity concerns the distribution and movement of electrons, and has little to do with the positively charged protons locked within the atomic nucleus.

True

The study of the distribution of fixed charges, or electrons that are at rest is

electrostatics

Just as all atoms are charged (neutral, positive, and negative), objects become charged by their

composite individual atomic charges.

There are instances, as when walking across a heavy rug in winter, when electrons are easily transferred (literally scooped up) onto another object. It is this type of distribution and redistribution of charged electrons that makes up..

electrification

The term electrification is used to

describe the process of electron charges being added to or subtracted from an object.

When one object has more electrons than another, it also has more negative charges. Therefore, it can be considered to be

negatively electrified, or to have a negative charge.

The concept of positive electrification,a positive charge, is more complicated because protons, which carry true positive charges, are not easily distributed. Therefore, a positive charge usually refers to something with a weaker negative charge, or fewer electrons. The so-called positively electrified, or charged, object has a

negative charge;it is just a weaker negative charge than the object with which it is being compared. It is less negative, and therefore termed positive, by comparison

It is important to remember that electrification is a relative term and that nearly all objects have

negative charges

both positive and negative, in equal distribution, it is considered to be

neutral; It has zero potential because the equally balanced charges have no potential to perform work and release energy.

what are the five fundamental laws of electrostatics?

1. Law of repulsion

2. The inverse square law

3. Law of distribution

4. Law of concentration

5. Law of movement

What is the inverse square law?

The force between two charges is directly proportional to the product of their magnitudes and inversely propor-

tional to the square of the distance between them.

-As a charged object gets further away, the influencing charge decreases because of the increased area it affects.

The inverse square law is expressed as:

1^1/1^2= D^2/D1

where:

I, = old intensity

1, = new intensity

D,2 = old distance squared

D,2 = new distance squared

what is repulsion- attraction law?

like charges repel, unlike charges attract

this inverse square formula is usually sufficient for radiographic needs, it is important to understand that the true relationship of the force between two charges is accurately expressed in Coulomb's law:

F = kq1q2/R^2

where:

F = electrostatic force in newtons

k = constant of proportionality (9 × 10°

for coulombs and meters)

q, and q, = charges in coulombs

R = distance in meters

This formula takes into account the true definition: the force between two charges (q1 and a2) is directly proportional to the product of their magnitudes (q, X q,), and inversely proportional to the square of the distance between them.

What is the law of distribution?

charges reside on the external surfaces of conductors and equally throughout nonconductors.

This law is a result of the effect of the repulsion-attraction law, as electrons, all with negative charges, attempt to repel each other as much as possible. In a solid conductor, this results in equal distribution on the surface, which is the point where electrons can obtain maximum distance from each other. In a nonconductor, such as a cloud, charge movement is not facilitated and equal distribution throughout the object results.

what is the Law of concentration?

The greatest concentration of charge will be on the surface where the curvature is sharpest.

If enough electrons congregate, they can induce _____ of the surrounding air and even discharge to the nearest point of lower concentration.

ionization

Therefore, x-ray tubes, which are subjected to extremely high charges, must not have sharp or rough edges where concentrations of electrons could occur and discharge at the wrong moment or in an undesirable direction.

The interior components of x-ray tubes are _____ and highly polished to eliminate sharply curved surfaces.

rounded

what is the law of moment?

Only negative charges move along solid conductors. Because the positive charges, the protons, are tightly bound inside the atomic nuclear field, only the electrons, which exist outside the nucleus, are easily moved along conductors.

What are the three methods objects can be electrified?

1. friction

2. contact

3. induction.

explain electrification by friction

Electrification by friction occurs when one object is rubbed against another and, due to differences in the number of electrons available on each, electrons travel from one to the other.

what are the ideal conditions for electron transfer?

Ideal conditions for electron transfer occur during cold weather when low humidity removes stabilizing electrons from the air, decreasing the resistance to electron movement between objects.

give an example of friction electrification

An example is a common trick that delights children-rubbing a balloon against a wool sweater will permit the balloon to stick to a wall. In low humidity, electrons will transfer from the wool to the balloon, giving it a negative charge, which can cause it to stick to a smooth wall with a relatively positive charge.

how you could you lessen the amount of friction on objects?

The solution to the problem is to increase the humidity, or the amount of water in the air, causing a slight condensation on all surfaces. This thin film of moisture becomes a pathway for the distribution of electrons.

why would you see an humidifier in a radiographic darkroom?

The use of a humidifier in a radiographic darkroom during cold weather thus helps eliminate electrostatic discharges that can cause artifacts on film.

explain electrification by contact.

occurs when two objects touch, permitting electrons to move from one to the other. This process is a simple equalization of charges, with both objects having similar charges after the contact.

what is an example of electrification contact?

Walking across a woolen carpet in a room with low humidity may cause shoes to scoop electrons from the carpet fibers that are then distributed over the entire body.

This is an example of electrification by friction. However, when a positively charged object with fewer electrons is touched, the contact will cause electrons to move to the less negatively charged object in an attempt to equally distribute the charges.

A metal doorknob or another person are examples of positively charged objects that would attract electrons from a person who had just walked across a rug. After the contact, both objects would have a more equal distribution of electrons. What causes this reaction?

caused by the individual force fields of the electrons satisfying the repulsion-attraction law over the entire surface of the conductors.

remember the replustion-attraction law means: like charges repel and opposite charges attract.

As soon as the oppositely charged objects are in close proximity, what happens?

the electrons often jump the gap in the form of a static discharge. This occurs as soon as the difference in charges becomes sufficiently great and the intervening distance sufficiently small.

what is static discharge?

The loss of static electricity as electric charges transfer from one object to another.

-In most cases, the static discharge releases excess energy in the form of light photons.

what is an electroscope?

an instrument for detecting and measuring electricity.

A simple device that illustrates the laws of electrostatics. It consists of a rod connected to a pair of thin, easily charged metallic leaves, which are protected from air currents by a glass flask.

When a charged object, such as the metallic rod in an electroscope, is brought into contact with the rod, the excess electrons obey the third law of electrostatics and distribute equally throughout the rod and leaves.

what is the 3rd law?

law of distribution

The resultant of the third law increase in the number of electrons present on both leaves in the electroscope causes the two leaves to obey the first law of electrostatics and, because they possess like charges, repel each other. Name the first and third law of electrostatic.

law one: repulsion-attraction law

law three: law of distribution

it is possible to see the two leaves of an electroscope move further apart. why might this happen?

If an electroscope is subjected to an intense beam of ionizing x-ray photons, the air becomes ionized. The ionized atoms draw electrons from the leaves, thus causing the charge on the leaves to be reduced. Consequently, the electroscope leaves relax and move closer together.

Define Electrification by Induction

is the most important method because it is the one used in the operation of electronic devices.

Induction is the process of electrical fields acting on one another without contact

Like atoms, force fields are a result of

the composite forces of the charges residing within the object. These force fields are called electric fields and they can cause induction.

When a strongly and a weakly charged object come close to one another, the electrical fields will begin to:

act on one another before contact occurs.

examples of induction

electroscope, balloon on wall

How does lightning occurs?

Lightning discharges occur as the masses of atoms making up the water vapor in clouds move rapidly through the atmosphere. Under conditions where many electrons are available, such as when there are numerous storm clouds, the movement of the water vapor atoms tends to cause electrons to be picked up or lost.

As an individual cloud becomes predominantly positively or negatively charged, it becomes a candidate for a huge electrostatic discharge.

Clouds often pick up electrons on their upper edges and lose them on their lower edges and vice versa. In these instances, the difference in charges makes the cloud a candidate for a cloud-to-cloud discharge as soon as

the insulating effect of the vapor between the two surfaces has been overcome. However, the most interesting part of lightning is cloud-to-ground discharges. The ground often develops a temporary opposite charge from the underside of the cloud because of the induction effect of the cloud on the ground. This causes the electrons to spread out, which in turn tends to rapidly increase the difference in charges between cloud and ground and can quickly overcome the insulating effect of the air between the cloud and the ground.

The result is lightning discharges occurring much more rapidly than if

induction had not taken place.

Lightning discharges do not occur as a single transfer of electrons from one area to another. Instead, vast numbers of

electrons may be transferred from cloud to ground, overloading the ground, which in turn transfers electrons back to the cloud, which again transfers them to the ground, over and over until the charges are somewhat equally distributed.

A short lightning discharge often transfers electrons back and forth between cloud and ground many times within a

microsecond.

Electrons that are moving in predominantly the same direction are often referred to as an

electric current.

what is a space from which air has been removed called?

a vacuum; Because it has few atoms to oppose electron flow, ( like air, which is an atom) it is especially useful in permitting electrons to reach the speed necessary to produce x-rays.

Some gasses (such as neon) will promote the drift of electrons from a negative electrode (cathode) to a:

positive electrode (anode).

These gasses also promote the drift of positive ions ( means to gain or lose an an electron) toward the negative cathode while negative ions move toward the:

positive anode.

An ionic solution can cause electrons to migrate:

to positive or negative poles during electrolysis, when they are subjected to an electric current.

Electrolysis becomes possible when:

two neutral atoms with complementary valences (eg, - 1 and +1) are brought together in a solution.

They become ions in the solution when the positive valence atom gives up an outer-shell electron to the negative valence atom.

The atom missing an electron becomes a positive ion (because a negative charge has been removed), whereas the one receiving the electron becomes a:

negative ion (because a negative charge has been added).

explain the migration of electrons during the electrolytic process comprising an electrical current.

When metallic rods are connected to a battery and immersed in the solution, the negative pole will attract the positive ions, whereas the positive pole will attract the negative ions.

what metallic conductor is the most common pathways provided for the movement of electrical current.

copper wire; the atoms of metallic conductors permit

valence electrons to drift.

In common household wiring, the actual physical movement is less than:

1 mm per second.

If individual electrons are drifting at less than a millimeter per second through a wire, why does a light bulb turn on instantly when the switch is flipped?"

the electromagnetic wave created by flipping the switch moves through the pre-filled wire at nearly the speed of light. This wave, not the individual electrons, instantly pushes the electrons at the bulb's end, causing it to light up.

The movement of electrons is facilitated by materials that easily permit electrons to flow. These materials are called

conductors and superconductors.

Examples of conductors are:

metals such as copper and aluminum.

electron movement is inhibited by materials that resist the flow of electrons. These nonconducting materials are called :

insulators

Examples of insulators:

plastic, rubber, and glass.

What is a semiconductor?

They have the ability to conduct under certain conditions and insulate under others. They result primarily from changes in the energy states of atoms, causing outer-shell electrons to move in a particular direction

An electrical circuit is a:

pathway (commonly copper wire) that permits electrons to move in a complete circle from their source, through resisting electrical devices and back to the source.

As in electrostatics, an electrical circuit must have an excess charge at one end and a:

comparative deficiency at the other to allow electrons to flow.

There are several sources of the excess electrons necessary to cause current flow: what are they?

Examples include a battery, which converts chemical energy to electrical; a generator, which converts mechanical energy to electrical; a solar converter, which converts solar photons to electrical energy; and an atomic reactor, which converts nuclear energy to electrical.

Electrons move from the highest concentration to:

the lowest concentration

electric current is described as going from positive to negative poles, whereas electron flow is actually from:

negative to positive poles. It is important to specify whether descriptions are of electrical current or electron flow, as they are exact opposites.

- Electrical current: This is the rate at which electric charge flows through a conductor (like a wire). It tells us how much charge is moving per unit time. The unit is the ampere (A), which equals 1 coulomb of charge passing per second.

- Electrical flow: This is a more general or informal way of describing the movement of electric charges. It doesn’t always specify how fast or how much is moving—it’s more about the idea that electrons (or charges) are in motion.

electrical current:

This is the rate at which electric charge flows through a conductor (like a wire). It tells us how much charge is moving per unit time. The unit is the ampere (A), which equals 1 coulomb of charge passing per second.

Electrical flow:

This is a more general or informal way of describing the movement of electric charges. It doesn’t always specify how fast or how much is moving—it’s more about the idea that electrons (or charges) are in motion.

The nature of the flow of electrons that make up an electric current can be described in many different ways. The most common factors used are:

are the quantity of electrons flowing, the force with which they travel, the amount of opposition to the current flow in the circuit, and the direction of travel.

The direction of travel of the electrons is defined as

as either direct current (DC), when all electrons move in the same direction, or alternating current (AC), when electrons move first in one direction and then reverse and move in the opposite direction.

What is direct current?

Current that flows in only one direction

What is alternating current?

A flow of electric charge that regularly reverses its direction.

electrical Current :book definition

The quantity, or number, of electrons flowing is sometimes referred to as the: Measurement of current is the number of electrons flowing past a given point per unit of time (usually per second).

What is the unit of current?

ampere, A;

The unit of current bears his name. (The French scientist André Ampère (1775-1836) did much original work in defining electricity and magnetism.

The ampere is sometimes called the amp for short and is represented by the symbol A.

1 ampere = 1 coulomb/1 second)

1 ampere flowing in a household wire causes:

6,240,000,000,000,000,000 electrons to move less than 1 mm per second should help in understanding the small size of electrons.

Diagnostic radiographic equipment utilizes _______ units to regulate the number of electrons available to produce x-ray photos.

milliamperage

The force with which the electrons travel is a function of the difference between the number of electrons in excess at one end of the circuit and the deficiency at.

the other end

what is the cause of the force of electron movement?

The attempt of the unequal forces to balance;

Because the difference is present while the source is connected into the circuit, there does not have to be an actual flow of current for the difference to exist.

Therefore, the simple potential for a difference is used to describe the force, or strength of movement, behind electrons.

what is the force or strength of electron flow define as? and why?

potential difference

The attempt of the unequal forces to balance;

Because the difference is present while the source is connected into the circuit, there does not have to be an actual flow of current for the difference to exist.

Therefore, the simple potential for a difference is used to describe the force, or strength of movement, behind electrons.

It should be remembered that potential difference continues to exist even when a switch is:

opened in a circuit, breaking the actual flow of electrons (current).

Because potential difference is the prime force causing electrical devices to convert electrical energy to mechanical, the term ____ _______ (emf) has also been used.

electromotive force

what is define as the total maximum difference of potential between the positive and negative ends of the electron source.

Electromotive force

The unit of potential difference is

Volts/voltage

volt is defined as:

joule per coulomb

true or false: A joule is the SI unit for both mechanical energy and work.

True

the force by which electrons travel can be described by the terms:

potential difference, electromotive force (emf), and voltage (V).

As the current flows along the circuit, the potential difference is reduced because the closer the electrons come to the deficient end of the circuit, the farther they are from the excess end and the closer they are to becoming part of the deficiency themselves. Define the deficient ends and excess ends.

Negative terminal (Excess Side): This terminal has an excess of electrons. During the chemical reaction inside a battery, electrons accumulate here, creating a negative charge and a lower electrical potential.

Positive terminal (Deficient Side): This terminal has a deficiency of electrons. It is the "destination" for the electrons, and its lack of electrons gives it a positive charge and a higher electrical potential.

why is High voltage is extremely dangerous?

because there does not have to be an actual flow of current for the potential difference to exist. This means high potential difference or voltage remains a hazard at all times.

true or false: All that is required for a high difference in voltage to achieve equalization is for a conductor to present itself. If this happens to be a patient who inadvertently uses a wet hand to grasp a cracked high-voltage cable or a radiographer who touches two connection points inside a control console, the shocking result is the same.

true

The amount of opposition to the current in the circuit is

called the:

resistance

What is the unit of resistance?

Ohm (Ω), 0 , omega

The technical definition of an ohm is

the resistance to a flow of current provided by a column of mercury 106.3 cm long with a diameter of 1 mm 0°C.

true or false: Resistance and impedance are the terms used to describe current opposition

true

The primary factors for electrical circuits are:

ability to conduct electrons, length of the conductor, cross-sectional diameter, and temperature

True or false: When the expression 1/R is used, the resistance of a DC ( direct circuit) circuit is measured as conductance, whereas that of an AC ( alternating circuit ) circuit is measured as admittance.

true

The SI unit for conductance( DC/ direct circuit) and admittance(AC/ alternating circuit) is:

the siemens;which is represented by the symbol S

The tendency of an atom to permit electrons nearby or within one of the orbital shells is the prime factor in determining:

conductivity, semiconductivity, and insulation properties.

The valence energy band (the outermost and sometimes next-to outermost orbital shell) not only determines the chemical properties of the atom, as discussed previously, but has much to do with:

conductivity as well.

Valence has much to do with the ability of a material to conduct electrons. Any element with one valence electron is a:

good conductor ; (e.g., copper, silver, and gold)

In addition, the farther the valence electron is from the nucleus, the better a conductor it is.

For example, gold is a better conductor than silver because its valence electron is in the sixth shell, whereas silver's is in the fifth shell. Silver is a better conductor than copper because copper's valence electron is in the fourth shell.

why is copper used as conductive than gold or silver?

Because copper has a higher melting point and is much cheaper, it is more commonly used than silver or gold.

There is also an area beyond the valence band that is not an orbital shell but is within the force field (area of influence) of the atom. What is this area called ?

that is referred to as the conduction band.