Electrical Fundementals Flashcards
What do all materials contain?
All materials contain both positive and negative charges, usually distributed evenly.
What is static electricity?
Positive and negative charges are unevenly distributed.
How can static electricity be generated?
Contact friction, or induction.
What happens when you rub a glass rod with fur?
The rod becomes negatively charged.
What happens when you rub a glass rob with silk?
The rod becomes positively charged.
What occurs when two materials are rubbed together?
Electrons move from one material to the other. (Static electricity)
How can a charged glass rod charge other objects?
Touching it to an uncharged object, a metallic bar.
What happens when a positively charged rod is brought near an uncharted metal bar?
It draws the bars electrons towards the rod, redistributing the charges within the bar.
What charge does one end of the metal bar have after being near a positively charged rod?
One end of the bar becomes positively , while the other end in negatively charged.
What do opposite charges do?
Attract to each other.
What do like charges do?
Repel.
What is a pith ball?
A lightweight ball, coated with a conductive material.
What does Coulomb’s law describe?
The force between two electrically charged bodies.
What does Coulomb’s law state?
The electrostatic force between two-point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.
How does charge magnitude affect the electrostatic force?
The force increases with the product of the magnitudes of the charges.
What does coulobms law calculate?
Force of attraction
Typical value of K?
9.0x10^9Nm^2/C^2
SI units for: force, charge, distance
Newton, coulombs, meters
How is conductivity classified among materials?
Materials with very low conductivity are classified as insulators.
What occurs when an electron enters a conductor?
electric current.
What is electric current?
The movement of electrons through a conductor.
What occurs when a conductor narrows, like in a light bulb filament?
Electrons move faster to maintain the same current leading to greater heating in a narrower section.
Is chemically pure water a good conductor of electricity?
No
What does tap water contain that effects ins conductivity?
Water molecules along with substances
What type of current is used to generate gases during electrolysis of water?
Direct current (DC)
What is the conducting substance is electrolysis called?
An electrolyte
What carries charge when an electric current flows through an electrolyte?
Inos
What are positive and negative ions called, and which direction do they flow?
Positive: cations, cathode
Negative: anions, anode
What is often emitted during gas discharge?
Visible light
What happens during collisions between high speed electrons and gas atoms?
Ionise the atoms producing more free electrons.
What is the process of creating large numbers of free electron and positive ions called?
Electron cascade.
What is a vacuum
No particles
What is voltage a measure of?
PD in electrical charge between two points.
What is electric current?
The rate of flow of electrical charge in a certain direction.
Unit of electric charge?
Ampere (A) amp
How is current defined?
The number of coulombs of charge flowing through the cross-section of a conductor I one second.
What is the symbol for electrical charge?
Q, measured in coulombs (C)
What is conventional current flow?
Direction of positive charge flow
How is potential difference measured?
Volts, between two points of a circuit.
Equation for current?
I=Q/t
Equation for resistance?
R=V/I
What is doping in their context of semiconductors?
The process of adding impurities to create semiconductors that produce more electrons (n-type) or more holes (p-type)
What is a photovoltaic cell?
A solar see that ruins light into electrical energy.
How is a photovoltaic cell structured?
Thin slice of n-type silicon placed over a thicker slice of p-type silicon.
What happens at the p-n junction of a photovoltaic cell?
When light falls on the p-n junction both electrons and hole flow across it generation an electromotive force (EMF)
What type of energy do thermoelectric generators utilise?
Thermal energy.
What happens when you rub an insulator?
Electrical charges separate, generating an EMF.
What are some hazards associated with static electricity?
Spark or shock
Where does sparking typically occur in an electric field?
At points and corners.
What is the piezoelectric effect?
Generation of voltage when pressure is applied to deform a piezo crystal.
How are charges collected in a piezoelectric all crystal?
Using m,arterial; like aluminium foil to form terminals.
Wheat are some applications of the piezoelectrical effect?
Record players, microphones, loudspeakers, lighters
How is voltage generated in terms of charge?
Voltage is generated by the separation of charge creating a potential difference between two points.
What are voltage generators based on chemical principles called?
Galvanic cells
Multiply galvanic cells?
Battery
Fletcher
Fletcher
What are the two main components of most electrical generators?
Static ring called ‘stator’, and a rotating set of coils on an axle known as the ‘rotor’
What type of voltage do most electrical generators provide?
Alternators
What is the phenomenon called when a conductor moves through a magnetic field and an EMF is induced?
Generator effect
What results from the deflection of electrons in a conductor moving through a magnetic field?
Electrical voltage.
What type of energy is converted into electrical energy in the generator effect?
Kinetic energy
How can the efficiency of EMF be improved in electromagnetic induction?
Coil of wire instead of a single conductor.
Applications of electromagnetic induction?
Field telephones
Can primary cells supply voltage without charging?
Yes
What determines the capacity of galvanic cells?
Construction and size
What is one disadvantage of zinc-carbon batteries?
Oxidises and leaks.
Alkaline batteries compare to zinc batteries in terms of energy?
Alkaline batteries can deliver up to 5 times more energy.
What can alkaline batteries leak?
Potassium hydroxide, so should be removed from devices if not being used from a long time.
What is a secondary cell battery?
Rechargeable battery
What is the voltage of a lead acid cell when charged and when discharged?
2.2V charged, and 1.83V discharged
What is the voltage of a nickel-cadmium cell when fully charged and when discharged?
1.2V charged, and 1V discharged
How are cells connected in series?
Unlike terminals
Total voltage in series?
Sum of the voltages
What happens to the current in a series circuit?
Constant
Main advantages of series?
Increases the total voltage
How are cells connected in parallel?
Like terminals
What happens to the voltage when cells are connected in parallel?
The same
What happens to the internal resistance in parallel?
Decreases
What is the effect of parallel connections on the current?
Larger current
What is source voltage
Total voltage generated by a power source
What causes internal resistance in power sources?
Electrolyte and plates
How does load current affect terminal voltage?
Load current increases, terminals voltage falls
How does LDR control the LED in a circuit?
LDR’s resistance increases therefore switching on the transistor and activating the LED
