Week 4: Electrostatics & Electrodynamics

Question 1

Electricity

Answer 1

Concerns the distribution and movement of electrons; protons and neutrons are secured in the nucleus of the atom and are not involved with electricity

Question 2

Electrostatics

Answer 2

Study of the distribution of fixed charges, or electrons that are at rest

Question 3

Electrification

Answer 3

Process of electron charges being added to or subtracted from an object

• When one object has more electrons than another, it is said to be negatively electrified, or to have a negative charge.
• The object that has fewer negative charges is said to have a positive charge in comparison to the object that has more of a negative charge, even though both objects contain negative charges.
• When discussing electricity, the terms negative and positive refer to the relationship between two objects, not their true atomic charges.

Question 4

Repulsion-attraction

Answer 4

-like charges repel
-unlike charges attract

Question 5

Inverse square law

Answer 5

As a charged object gets further away, the influencing charge decreases because of the increased area it affects. The force between two charges is directly proportional to the product of their magnitudes and inversely proportional to the square of the distance between them

Question 6

Distribution

Answer 6

Charges reside on the external surfaces of conductors and equally throughout nonconductors. With conductors, this is a result of the effect of the repulsion-attraction law, as electrons with their negative charges attempt to repel each other as much as possible

Question 7

Concentration

Answer 7

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

Question 8

Why are the interior of x-ray tubes rounded and polished?

Answer 8

to eliminate sharply curved surfaces to avoid unwanted electrical discharges inside the x-ray tube

Question 9

Movement

Answer 9

Only negative charges (electrons) move along solid conductors. Protons and neutrons are held within the nucleus of the atom.

Question 10

Friction

Answer 10

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

•Example- rubbing a balloon against a wool sweater can permit the balloon to stick to the wall. In low humidity, electrons transfer from the wool to the balloon, giving it a negative charge, which causes it to stick to the wall that
has a relatively positive charge.

Question 11

Contact

Answer 11

Electrification by contact occurs when two objects touch, permitting electrons to move from one to the other. This process results in an equalization of charges, with both objects have similar charges after contact.

• Example- Contacting a less negatively charged doorknob after shuffling across a carpet and picking up an excess number of electrons on the person, results in movement of the excess electrons on the person to the doorknob as negative charges attempt to distribute themselves.

Question 12

T or F: actual physical contact does not have to occur between two objects because electrons can jump the gap between objects like with static discharge

Answer 12

True

Question 13

Induction

Answer 13

Electrification by induction is the process of electrical fields acting on one another without contact. Every charged body is surrounded by a force field (electric field) and these fields can cause induction. When a strongly and weakly charged object come close to one another, the electrical fields will begin to act on one another before contact begins

Question 14

Electrodynamics

Answer 14

Study of electric charges in motion. If there is an excess number of electrons on one end of a conductor, electrons will move along the conductor in the same direction to redistribute themselves

Question 15

Conductors

Answer 15

Materials that facilitate the movement of electrons. Metallic conductors, such as copper wire, are the most common pathways for the movement of electrons. The atoms of metallic conductors permit valence electrons to drift. The movement of electrons is called electric current. Examples- gold, silver, aluminum.

Question 16

Insulators

Answer 16

-Materials that inhibit electron movement.
-Examples- plastic, rubber, glass.

Question 17

Semiconductors

Answer 17

-Materials that can conduct under certain conditions and insulate under others
-Examples- silicon, germanium

Question 18

Electrical circuit

Answer 18

A pathway that permits electrons to move in a complete circle from their source, through resisting electrical devices, and back to the source. An electric circuit must have an excess charge at one end and a comparative deficiency at the other to allow electrons to flow.

Question 19

Examples of electron sources

Answer 19

• Battery- converts chemical energy to electrical
• Generator- converts mechanical energy to electrical
• Solar converter- converts solar photons to electrical
• Atomic reactor- converts nuclear energy to electrical

Question 20

Current flow

Answer 20

-Electrons move from the highest concentration to the lowest. The quantity of electrons flowing past a given point per second is referred to as current.
-Represented by the ampere or amp (A).
-1 A = movement of 6.24 X 10 to the power of 18 electrons per second past a given point.

Question 21

Conventional electric current is described as going from _________ to _________ poles, whereas electron flow is actually from _________ to ________ poles.

Answer 21

-Positive to Negative
-Negative to Positive

Question 22

Direct current (DC)

Answer 22

All electrons move in the same direction through a circuit. A circuit powered by a battery is a DC circuit, as electrons travel from the negative pole to the positive pole.

Question 23

Alternating current (AC)

Answer 23

Electrons change directions several times per second.
AC is expressed by the Hertz (Hz). 1 Hz = 1 cycle per second (cps). In the United Stated 60 Hz current is supplied to our electrical outlets. A circuit powered by a generator is an AC circuit.

Question 24

Amperes or amp (A)

Answer 24

Describes the quantity of electrons moving past a given point per second. 1 A = movement of 6.24 X 1018 electrons per second past a given point

Question 25

Potential difference

Answer 25

Term to describe the force, or strength of electron flow

• It is also referred to as electromotive force (emf), which is the total maximum
difference of potential between the positive and negative ends of the electron source.
• The unit of potential difference is the volt (V); voltage is also used to describe
potential difference.
• The terms potential difference, electromotive force (emf), and voltage can be used interchangeably.

Question 26

Resistance

Answer 26

Also called impedance; the amount of opposition to current flow
• Unit of resistance is the ohm (Ω).
• Ability to conduct electrons- an atom’s valence determines its conducting ability. An atom with a +1 valence (1 electron in the valence shell) is a good conductor.
• The farther the valence electron is from the nucleus, the better the conductor.
• Conductors have conduction bands that are populated with free electrons. Solids make the best conductors.

Question 27

Length of conductor

Answer 27

As the length of the conductor doubles, the resistance will double. The length of the conductor has a directly proportional relationship to resistance.

Example- a short garden hose will spray water with more force than a long garden hose

Question 28

Cross-sectional diameter of conductor

Answer 28

As the cross-sectional diameter doubles, the resistance will be halved. The cross-sectional diameter of the conductor has an inversely proportional relationship to resistance.

Example- a garden hose with a small diameter will impede(slow) water flow more than a large diameter hose

Question 29

Temperature of conductor

Answer 29

Increased temperature increases free electron collisions, creating more resistance. As conductor temperature increases, resistance increases.

Question 30

Series circuit

Answer 30

links resistance devices (R₁, R₂, etc.) one after another through just one conductor branch for the entire circuit.

Example- When thinking of a strand of lights, when a single-series wired light burns out, it breaks the circuit, and all the lights go out. When a single parallel wired light burns out, it breaks the circuit in its parallel branch only and the other lights continue to operate.

Question 31

Parallel circuit

Answer 31

Each resistance device (R₁, R₂, etc.) has its own individual branch in the circuit

Example- When thinking of a strand of lights, when a single-series wired light burns out, it breaks the circuit, and all the lights go out. When a single-parallel wired light burns out, it breaks the circuit in its parallel branch only and the other lights continue to operate.

Question 32

Ohm’s law (V=IR)

Answer 32

• A mathematical relationship between the factors of current, potential difference, and resistance applies to all circuits.
• Ohm’s law is represented mathematically by: V=IR

   V= potential difference in volts (V)
   I= current in amperes (A)
   R= resistance in ohms (Ω)

Question 33

Power P=IV

Answer 33

• The total power of a circuit is expressed in watts (W). Common household appliances operate between 500 W and 2,000 W.
• Power is represented mathematically by: P=IV

   P=Power in watts (W)
   I=current in amperes (A)
   V=potential difference in volts (V)

Question 34

Ground (zero potential)

Answer 34

The Earth behaves as a huge reservoir for stray electric charges and is termed the electric ground. Electrical grounding is a backup pathway that provides an alternative route for current to flow if there is a fault in a circuit.

Question 35

Circuit breaker (fuse)

Answer 35

Devices constructed to permit the breaking of a circuit before a dangerous temperature is reached. Circuit breakers simply pop open and can be reset once the cause of the problem has been corrected in the circuit. Fuses are constructed with a metal tab that will melt when dangerously heated, thus breaking the circuit. Fuses are not reusable and must be replaced.

Question 36

Potentiometer (rheostat)

Answer 36

A variable resistor that permits a variable contact to slide along a series circuit of resistance coils. The mA selector in the circuit is an example.

Question 37

____________ conductors, such as _________ wire, are the most common pathways for the movement of electrons.

Answer 37

Metallic, Copper

Question 38

The movement of electrons is called

Answer 38

electric current

Question 39

The force between two charges is __________ proportional to the product of their magnitudes and ____________ proportional to the square of the distance between them

Answer 39

directly, inversely