CH 4
Q: What is Electrostatics?
A: The study of stationary electric charges.
Q: What is Electrodynamics?
A: The study of electric charges in motion.
Q: The smallest units of charge exist with the _____ and the _____.
A: Electron, proton.
Q: What System International unit are electric charges measured with?
A: Coulomb.
Q: One coulomb is equal to what?
A: electrons.
Q: What are conductors?
A: They have a large number of free electrons like copper and gold.
Q: What are insulators?
A: They have very few free electrons like glass and plastic.
Q: What are the five general principles of electrostatics?
A:
Like charges repel and unlike charges attract.
The electrostatic force between two charges is directly proportional to the product of their quantities and inversely proportional to the square of the distance between them.
Electric charges reside only on the external surface of conductors.
The concentration of charges on a curved surface of a conductor is greatest where the curvature is great.
Only negative charges (electrons) are free to move in solid conductors.
Q: Why does electrification occur and what are ways that it can happen?
A: Occurs when they gain a net positive or a net negative charge and can happen by friction, by contact, or by induction.
Q: For electric current to move what must exist?
A: An electric potential.
Q: What is Electric Potential?
A: The ability to do work because of a separation of charges.
Q: What is Current?
A: An expression of the flow of electricity.
Q: What is Resistance?
A: That property of an element in a circuit that resists or impedes the flow of electricity.
Q: How is x-ray production achieved?
A: By the manipulation of electricity.
Voltage & Current
Q: What is the unit of measure for electrical potential?
A: Volts.
Q: What is the unit of measure for current?
A: Ampere.
Q: Who is Volta?
A: Italian physicist who invented the battery, volts was named after him.
Q: Define a volt.
A: The potential difference that will maintain a current of in a circuit with a resistance of .
Q: Volts is equal to what?
A: Joules.
Q: What is kVp?
A: Kilovoltage Peak.
Q: What does kilovoltage peak do?
A: It determines how the beam penetrates the body part, controls contrast on the film image and influences contrast in the digital image.
Q: Who is Andre-Marie Ampere?
A: French physicist who made significant contributions to the study of electrodynamics, ampere was named after him.
Q: Define ampere.
A: flowing by a given point in .
Current
Q: What happens in a vacuum tube?
A: Electrons tend to jump the gap between oppositely charged electrodes.
Q: What are the types of current?
A: Direct Current (DC) and Alternating Current (AC).
Q: What is DC?
A: Direct Current that flows in only one direction.
Q: What is an example of DC?
A: A battery because it moves from a negative terminal to the positive terminal.
Q: What is AC?
A: Alternating Current that changes direction in cycles as the electric potential of the source changes.
Q: What is an example of AC?
A: Electricity in USA homes that flows into homes and alternates at .
Resistance & Ohm's Law
Q: How is Resistance measured?
A: In ohms.
Q: Define ohm.
A: The electrical resistance equal to the resistance between two points along a conductor that produces a current of when a potential difference of is applied.
Q: What does Ohm's Law state?
A: That the potential difference across the total circuit or any part of that circuit is equal to the current multiplied by the resistance.
Electromagnetism
Q: What is a Solenoid?
A: A wire twisted into a coil to strengthen its magnetic field.
Q: What is an Electromagnet?
A: A solenoid with an iron core inside it, making a temporary magnet powered by electricity.
Q: What is Electromagnetic Induction?
A: Creating an electric current by moving a conductor through a magnetic field.
Q: To increase the induced voltage in a magnetic field you need these things.
A: More coils, more speed, more strength.
Q: What four things does the amount of resistance of a particular conductor depend on?
A: Material, length, cross-sectional, and temperature.
Circuits & Electrical Devices
Q: What is a Closed Circuit?
A: Is complete and allows for electricity to flow (turn on switch).
Q: What is an Open Circuit?
A: Is broken and does not allow electricity to flow (turn off switch).
Q: What is a Battery?
A: A device that produces electrons through a chemical reaction, stores an electric charge for the long term, and provides an electric potential.
Q: What is a Capacitor?
A: Temporarily stores an electric charge.
Q: What is a Diode?
A: A "one-way valve" device that allows electrons to flow in only one direction.
Q: What are Fuse and Circuit Breaker?
A: Are protective and emergency devices that break or open the circuit if there is a sudden surge of electricity to the circuit or device.
Q: What is a Resistor?
A: Inhibits the flow of electrons, thereby precisely regulating the flow of electricity through that part of the circuit where it is placed.
Q: What is a Rheostat?
A: Simply an adjustable or variable form of resistor.
Q: What is a Switch?
A: A device that opens a circuit (breaks the pathway).
Q: What is a Transformer?
A: A device that can increase or decrease voltage by a predetermined amount.
Q: What is Grounding?
A: A process of connecting the electrical device to the earth via a conductor.
Magnetism
Q: What is Magnetism?
A: The ability of a material to attract iron, cobalt, or nickel.
Q: What is the nature of magnetic materials?
A: The orbital electrons of their atoms spin in predominately one direction.
Q: What are Magnetic Dipoles?
A: Atoms pointing in the same direction creating tiny magnets.
Q: What are Magnetic Domains?
A: A group of atoms or dipoles whose tiny magnetic effects are lined up in the same direction.
Q: What is Flux?
A: A magnetic field that consists of lines of force in space.
Q: Lines of flux travel from _____ → _____ inside the magnet.
A: S → N.
Q: Lines of flux travel from _____ → _____ outside the magnet.
A: N → S.
Q: Lines of flux in the same direction do what?
A: Repel each other.
Q: Lines of flux in opposite direction do what?
A: Attract each other.
Q: The magnetic field is measured in what SI unit?
A: Tesla (T).
Magnetic Materials
Q: What are Nonmagnetic materials?
A: Materials that are not attracted to magnetic fields at all: glass, wood, and plastic.
Q: What are Diamagnetic materials?
A: Materials that are weakly repelled by magnetic fields: water, mercury, and gold.
Q: What are Paramagnetic materials?
A: Materials that are weakly attracted to magnetic fields: platinum, gadolinium, aluminum.
Q: What are Ferromagnetic materials?
A: Materials that are strongly attracted to magnetic materials: iron, cobalt, and nickel.
Electromagnetic Induction
Q: The principle of electromagnetism was identified by whom?
A: Danish physicist Hans Oersted (compass).
Q: What are the forms of electromagnetic induction?
A: Mutual induction and self-induction.
Q: What is Mutual Induction?
A: Uses coils and is the induction of electricity in a secondary coil by a moving magnetic field.
Q: What is Self-Induction?
A: More complex, a changing current inside a single coil creating a second current that fights against itself.
Q: What are Electric Generators?
A: Devices that convert mechanical energy into electrical energy.
Q: What is Lenz's Law?
A: States that induced current flows in a direction that opposes the action that induced it.
Q: What are Electric Motors?
A: Devices that convert electrical energy to mechanical energy through electromagnetic induction.
Q: What does a Step-up transformer do?
A: Increases voltage.
Q: What does a Step-down transformer do?
A: Decreases voltage.
Q: Change in voltage and current is an _____ relationship.
A: Inverse.