Section 1 Flashcards
What is the natural charge of Atoms and Molecules
Neutral
What allows the transfer of charge between Atoms and molecules?
Friction
What are Protons?
Positively charged particles in the Nucleus
What is the charge of a proton
+1.602 x 10^-19 Coulombs
What are Neutrons
Neutrally charged particles in the Nucleus
What are Electrons?
Negatively charged particles orbiting the Nucleus in Shells
What is the charge of an Electron
-1.602 x 10^19 Coulombs (same as proton charge but Negative)
Proton and Electron charge have the same Magnitude, what is this known as and what is its value?
Elementary Charge
1.602 x 10^-19 Coulombs
What is Atom Mass decided by?
The number of Protons and Neutrons
Which component of an Atom has almost no mass?
Electrons
What is a charged atom called?
An Ion
What is a Molecule
ELECTRICALLY NEUTRAL group of 2 or more Atoms joined by CHEMICAL BONDS
What is a charged molecule called?
An Ion
What is a Cation?
A POSITIVE Ion created by LOSING an electron
What is an Anion?
A NEGATIVE Ion created by GAINING an electron
What is a Free Electron?
Electron moving freely around the structure of a material, not contained in a shell
What is a Compound?
2 or more Elements combined CHEMICALLY
What are the 2 types of compound bonds?
Ionic and Covalent
What is the Structure of Metal conductors
-CRYSTAL LATTICE
-Closely packed atoms form GIANT structure
-Regular pattern
-Outer shells of Atoms OVERLAP (allows free electron movement through Lattice)
-Sea of FREE ELECTRONS
What does High electron mobility result in?
High conductivity of both Electricity and Heat
How many Valence Electrons do atoms in good conductors have?
Less than 4
What is a Semi-conductor?
Material with a conductivity between that of a good conductor and a good insulator
3 Factors affecting conductivity of Semi-conductors?
Temperature, Doping and Heat (higher temp =higher conductivity)
How many Valence electrons do Atoms in Semi-conductors generally have?
4
Where are Semi-conductors located on the Periodic Table?
Between Metals and Non-metals
What is the structure of an Insulator?
-ELECTRONS are tightly connected to the atoms or molecules and cannot break away
-No FREE ELECTRONS = No conductivity of ELECTRICITY
How many Valence electrons do Insulators generally have?
More than 4
What are 2 examples of Semiconductors?
Silicon and Germanium
What are 2 examples of Insulators?
Mica and Porcelain
What is Static Electricity?
Uneven charge distribution resulting in a net positive or negative charge in a material
What are 3 ways to generate Static electricity?
Contact, Friction or Induction
What are Pith Balls?
Lightweight balls with a surface coated in Conductive Material that are used in conjunction with a CHARGE ROD to demonstrate how opposite charges ATTRACT each other and similar charges REPEL eachother
What is Coulomb’s Law?
“The magnitude of the electrostatic force of attraction between two-point charges is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between them”
What is the Electric constant (K) in Coulomb’s law?
K = 9.0 x 10^9Nm^2/C^2
What direction does Electrostatic force cause electrons to move in a conduction solid?
From the Negative to positive pole
What does it mean when a Current is constant?
The same number of electrons per second flow through regardless of the cross-sectional area, where the conductor narrows, electrons move faster to maintain constant current.
What happens to chemically pure water when an electrical current passes through it?
It decomposes into Hydrogen and Oxygen
What happens when a DC current is passed through chemically pure water?
A high development of Hydrogen forms at the Negative pole and a Low development of Oxygen forms at the Positive pole
How does adding Acids, Bases or Salts affect the conductivity of water?
Improves the conductivity and increases the Decomposition of compounds
What is Electrolysis?
The Decomposition of chemical compounds via an electric current
What is an Electrolyte?
The conducting substance during Electrolysis
What is Electrolysis used for?
-Electroplating
-Charging batteries
-Producing substances like Chlorine, Hydrogen or Sodium Hydroxide
What carries the charge when an Electric current flows through an electrolyte?
The Ions
What direction do Cations (Positive Ions) flow through an Electrolyte?
From Anode (positive) to Cathode (Negative)
What direction do Anions (Negative Ions) flow through an electrolyte?
From Cathode (Negative) to Anode (positive)
What does a potential difference across a low pressure gas cause?
A steady current
What is Gas discharge?
The name for Electrical conduction in Gases
What does Gas discharge often emit?
Visible light
What devices are designed to creat light vis gas discharge?
Gas-discharge Tubes
What are Gas-discharge tubes usually filled with to create different colours?
Neon or Helium
How does a Gas Discharge tube work?
-Free electrons accelerate and collide due to low pressure and high Potential Difference
-This forms more free electrons
-Free electrons recombine with Positive Ions and release energy
-Energy releases as Electromagnetic radiation and visible light
-Some electrons and Ions read ends of the tube, carrying charge and creating an Electric Current through the gas.
What are Fluorescent tubes?
-Gas-discharge tubes with an inner surface coated with Fluorescent material
-This absorbs electromagnetic radiation and re-emits a broad spectrum of visible light
-These emit white light instead of coloured
What device uses charged particles moving through a vacuum to visualise electrical processes
-Oscilloscopes
What are 3 advantages of Electron beam oscilloscopes?
-Easy to operate
-Versatile
-Shock Resistant
What is a Braun Tube?
-An Electron beam tube made up of a Vacuum in a glass bulb with 2 electrodes
-Cathode and Anode connected to an external Potential Difference
-Heating the cathode releases free Electrons
-These accelerate toward Anode creating a current flow through the Vacuum
What is an Electron Gun?
-A further development of the Braun tube
-Focuses electrons into a narrow beam
-Used in oscilloscopes and Television tubes
How does a CRT work?
-Uses an electron gun to accelerate beam of electrons toward a screen
-Screen is painted with Fluorescent paint, produces light where beam strikes
-Beam direction controlled via potential difference between plates on the X and Y axis
What is the force that moves electrons through a circuit?
-Voltage
What is equal to the Terminal potential difference when no current flows?
-The Electromotive Force (EMF)
What three electrical principles use Volts (V) as their SI unit?
-Voltage
-Electromotive Force (EMF)
-Potential Difference (PD)
What is the equation for Voltage?
Voltage (V) = Energy transferred in Joules (E) / Charge in Coloumbs (Q)
V = E / Q
What are the 2 possible SI units for Voltage?
-Volts (V)
-Joules per Coulomb (J/C)
What are the 2 classifications of Voltage?
-Potential Difference (PD)
-Electromotive Force (EMF)
What are the 2 kinds of Electric Voltage?
-Direct Current (DC)
-Alternating Current (AC)
Which kind of Electric Voltage maintains the same polarity over time?
-Direct Current (DC)
Which kind of Electric voltage has magnitude and Polarity that change over time?
-Alternating Current (AC)
What is the Voltage of Supply known as?
-Electromotive Force (EMF)
What is EMF a measure of?
-The energy transferred to the circuit from other forms of energy by the supply
-No. of Joules transferred to each coulomb of charge separated by the supply
What does an Electrical Supply do?
-Separates charges
-Moves electrons from the Negative pole to the positive pole within the supply while maintaining EMF across the poles
How can an Electrical supply be achieved mechanically?
-By a Generator converting kinetic turbine energy to electrical energy in the circuit
How can an Electrical Supply be achieved chemically?
-By Galvanic cells converting chemical energy in the cell to electrical energy in the circuit
What is a Battery?
-A combination of Galvanic cells
-Also sometimes refers to a single Galvanic cell
What is potential difference caused by?
A deficiency of Electrons at one point and an Excess of Electrons at another
Can Potential Difference occur when no current is present?
-Yes, it is the energy that can potentially be transferred if a current flows and as such doesn’t require current to exist.
What are 2 ways to indicate a measured Voltage?
-Pointer deflection (Analogue meter)
-Numerical readout (Digital meter)
What level of Resistance do Voltmeters have?
-Very high (considered infinite in equations)
How do you connect a Voltmeter to a circuit?
-In parallel with the terminals of a power source and/or load
What is the common voltage of a Radio Aerial?
0.1 to 1.0 millivolts
What is the common voltage of a single cell battery?
-1.5 Volts
What is the range of common mains supply voltage?
-115 to 230 Volts
What is the range of common voltage of an Overhead Line?
-6 to 380 kilovolts
What is the common range of voltage of lightning?
-10 to 120 Megavolts
What is Current?
-The rate of flow of Electrical charge in a certain direction
What is Current defined as?
-The number of Coulombs of charge flowing through the Cross-section of a Conductor in one second
What is the equation for Current?
Current in Amperes (I) = Amount of charge in Coulombs (Q) / time taken in seconds (t)
I = Q / t
What are the 2 possible SI units for Current?
-Ampere (A)
-Coulombs per second (C/s)
What 2 Electrical characteristics does current depend on?
-The EMF of the supply
-The Resistance of the Circuit
What does an increase in EMF do to the Current in a circuit?
-The Current increases
Type of charge flow in Conductive solids?
-Electron Currents
Type of charge flow in Conductive liquids?
-Ion Currents
Type of charge flow in conductive gases?
-Electron and Ion Currents
Type of charge flow in a Vacuum?
-Electron and Ion currents
The movement speed of charge carriers (Electrons and Ions) depends on what 4 factors?
-Conductor Material
-Conductor Cross-Section
-Potential Difference
-Temperature
How do you connect an Ammeter or Current meter to a circuit?
-Connect it in series to measure current
Can a circuit be opened at any point to insert an Ammeter?
-Yes
What type of Ammeter must be installed with the proper polarity? (positive connection to positive pole, negative connection to negative pole)
-DC Ammeter
How many electrons per second is 1 Ampere?
6.24 x 10^18 Electrons
What is needed to achieve the same current in a higher resistance circuit?
-A higher Potential Difference
Equation for Resistance?
Resistance in ohms (R) = Voltage in Volts (V) / Current in Ampere (I)
R = V / I
Equation for Resistance?
Resistance in ohms (R) = Voltage in Volts (V) / Current in Ampere (I)
R = V / I
What are the 2 SI Units that can be used for Resistance?
-Ohms
-Volts per Ampere (V/I)
How does Resistance work?
-Free electrons in a circuit collide with Ions and are slowed
-The Kinetic energy is transferred to Thermal energy in the conductor
What happens in regards to Resistance as Atomic density increases?
-Resistance increases due to less space between the Ions in the conductor resulting in a higher braking effect
What happens to resistance if Cross-sectional area is reduced?
-Resistance Increases
What is Conductance?
-The Reciprocal of Resistance
-High Resistance = Low Conductance
-Low Resistance = High Conductance
What is the SI Unit for Conductance?
-Siemens (S)
What is the equation for Conductance?
Conductance in Siemens (G) = 1 / Resistance in ohms (R)
G = 1 / R
What are the 2 SI Units for Charge?
-Coulomb (C)
-Amp-seconds (As)
What is the equation for current?
Current (I) = Charge (Q) / time (t)
I = Q / t
What is a common non-SI Unit for charge?
-Amp-hours
What is the equation for charge?
Charge (Q) = Current (I) x time (t)
Q = I x t
How many Ampere-seconds are in 1 Coulomb of charge?
-1
-1 Coulomb = 1 Ampere-second
How many Coulomb in one Ampere-hour of charge?
-3600C
-3600C = 3600As = 1 Ampere-hour
What is Conventional current flow?
-The direction Positive charges move in
-Positive to negative direction
What is Electron current flow?
-The direction Electrons move in
-Opposite to Conventional flow
-Negative to Positive direction
Describe the movement of Positive and Negative charges in Metals?
-Positive charges are FIXED
-Negative charges (electrons) are the only charge that moves in metals
What does direction of Electron flow depend on?
-The Polarity of the applied voltage
What does reversing the Polarity of a circuit at equal intervals cause and what is it called?
-The electrons will Periodically change flow direction, reversing current flow
-This current flow is called AC Current
What may happen if Light hits a Semiconductor?
-It causes charge separation
-It generates Electricity
How is charge passed through a Semiconductor?
-Free electrons and holes are generated as covalent bonds break down from vibration.
-Electrons move from one hole to the next, effectively moving the hole in the opposite direction.
How does Light increase the conductivity of Semiconductors?
-Transfers to Thermal energy in the Semiconductor
-Increases rate of vibrations which increase the rate of bond breakdown
-Forms more Free electrons and holes to carry charge, increasing conductivity
What is Doping in relation to Semiconductors?
-Adding Impurities to create Semiconductors that produce more Electrons or more Holes
What are the 2 types of Semiconductors created by doping?
- N-Type (Negative): Produce more Electrons
- P-Type (Positive): Produces more Holes
What are Photovoltaic cells made up of?
-Thin slice of N-type Silicon over a thicker slice of P-type Silicon
What happens when Light hits the P-N Junction of a Photovoltaic cell?
-Both Electrons and Holes flow across the junction
-EMF is generated as a result
What is the purpose of the strips of metal at the top and bottom of the Photovoltaic cells in solar panels?
-They act as terminals, allowing an external circuit to be connected to the panel so the Solar panel can provide a source of power to the circuit
How can Thermal energy in a material be transferred directly into Electrical energy in a circuit?
-Via the Thermoelectric Effect
How do Thermocouples generate current in an attached circuit?
-Two different metals are twisted to form a Junction
-A small EMF is produced due to the difference in how closely the electrons are bound to their atoms in each material
-EMF increases as temperature increases
-A small current is generated
Why are thermocouples useful to accurately measure small temperature changes?
-The EMF they produce increases with temperature in a very predictable way.
-The current they produce is small but precise.
What are Thermoelectric Generators made out of?
-Semiconductor materials in a similar construction to Photovoltaic cells but using Thermal Energy instead of Light
How much electricity is generated by Thermoelectric generators?
-Moderate amounts
-Not enough for High power applications
What may rubbing an Insulator cause?
-Charge separation
-Source of EMF
-Very high voltages up to 1000Volts
-Can cause Electrostatic damage to components
When is Static Electricity generated?
-When 2 materials contact or Separate and at least one is a poor conductor
-When Insulating liquids or gases flow
What does the Voltage between 2 bodies at a different charge form?
-An Electric Field between the 2 bodies
What is an Electric Field?
-The area in which an Electric charge would feel the Attractive or Repulsive force due to Coulomb’s Law
What do the arrows on an Electric field show?
-The direction of the force on a positive charge
What happens if an Electric Field becomes too strong?
-Electrons move through the air towards the Positively charged body
-Sparking occurs
Where are Electrical fields strongest?
-At points or corners (eg Aircraft wingtips)
What do Static dischargers do on Aircraft?
-Dispel Static charges built up from Friction between an aircraft and the air
What type of crystal generates a Voltage when Pressure deforms it?
-Piezo Crystal
What is the Piezoelectric effect?
-A Reversible process
-Mechanical Stress separates charges within the crystal
-This generates an EMF
What happens when Voltage is applied to a Piezo crystal?
-Internal Mechanical Strain is generated
How are charges collected from Piezo crystals?
-Collected at Terminals across its surface
-Made from materials like Aluminium Foil
What can applying a Voltage across a Piezo crystal be used to control?
-Very small and precise mechanical movements
What happens when 2 different metals are immersed into a conductive liquid?
-A Voltage is generated between the 2 Electrodes
What happens to metals like Zinc that tend to force Positive metal Ions into the solution when acting as an Electrode?
-They become Negatively charged
What happens to metals like Copper, which tend to extract Positive metal ions from the solution when acting as an electrode?
-They become Positively Charged
What are voltage generators based on chemical action called and what are their 2 types?
-Galvanic cells
- primary cells
- secondary cells
At what angle does a Conductor have to move through a magnetic field in relation to it to induce an EMF across the conductor? And what is this known as?
-At a right angle to the direction of the magnetic field
-Generator effect
What is the principle behind Dynamo and Alternator operation?
-Generator Effect
What within a Conductor is perpendicular to both the Magnetic field direction and the movement of the Conductor?
-The Force causing electron deflection in the conductor and resulting in Generator Effect
What is used to make Generator effect more efficient?
-A coil of wire rather than a single conductor
What form of Voltage generation is the operating principle of all Generators?
-Electromagnetic Induction
What 3 characteristics can be increased to Increase the voltage generated by Electromagnetic induction?
-Magnetic field strength
-Movement speed
-Length of the conductor
What is a Stator in a generator?
-Electromagnets in a static ring around the outside
What is a Rotor in a Generator?
-A rotating set of coils on an axle running through the Stator
Primary cell characteristics
-Can supply voltage immediately without charging
-Cannot be recharged (Electrochemical process not reversible)
-Capacity depends on construction and size
What is a Dry cell?
-Cell where the electrolyte is a paste rather than a liquid
