topic test - electricity Flashcards
electrostatics
study of electrical charges at rest, forces existing between charges, and the electric fields associated with them
electric charge
extent to which matter has greater or fewer electrons than protons
law of electric charges
“like charges repel, opposite charges attract”
electric force
forces between electrostatically charged objects, dependent on:
- amount of charge
- distance between charges
static electricity
presence of net charge in an object due to imbalance of charge on atoms, associated with the movement of electrons either away from or towards the atom
charge by friction
rubbing insulators for electron transfer, “wiped” electrons
by rubbing two insulators hard against each other, electrons on the outside of both get “wiped” off and transferred
one object gains electrons (negative) and the other loses electrons (positive)
identified by triboelectric series, where substances higher up are more likely to lose electrons and become positive
charge by conduction
electron transfer by direct contact
when a charged object comes in contact with a neutral object, it either receives (if positive) or donates (if negative) electrons to the neutral object, causing it to gain charge, and then once removed, since electron exchange is stopped, the once-neutral object acquires the same charge
charge by induction
electron transfer without direct contact (induces charge, then forces of attraction and repulsion by electric fields)
must be for conductors only
inducing positive charge
electron rich, negative charged rod brought near a neutral conductor
by electrostatic repulsion, the negative charge on the rod will repel electrons in the conductor, forcing them to move to the extreme end of the conductor (furthest away from rods)
conductor is then connected to ground whilst still positioning negative rod nearby
all the electrons gathered in the slightly negative side will flow to the earth (grounding)
connection to earth is then removed, so no more movement of electrons can occur, and negative rod is moved away from conductor
remaining electrons redistribute themselves evenly, but since less electrons are present, there is a net positive charge
inducing negative charge
electron poor, positively charged rod brought near a neutral conductor
by electrostatic attraction, the positive charge on the rod will attract electrons in the conductor, forcing them to closest to the rods
conductor is then connected to ground whilst still positioning positive rod nearby
electrons from earth will flow into the conductor, due to electrostatic attraction to the slightly positive side
connection to earth is then removed, so no more movement of electrons can occur, and positive rod is moved away from conductor
remaining electrons redistribute themselves evenly, and due to excess of electrons there is a net negative charge
grounding
connected to earth by wire to neutralise charged conductors, due to electrons flowing into earth
conductors
materials in which electrical charges are free to move throughout, thus conducting electricity (low resistance to current flowing)
e.g. ionic compounds, plasma, metal
cannot be easily charged by friction, since the electrons can easily move
insulators
materials in which electrical charges are NOT free to move, thus not conducting electricity (high resistance to current flowing)
e.g. rubber, corks, cloths
can easily be charged by friction, by retaining charge from electrons
law of conservation of charge
net charge of isolated system remains constant
kirchoff’s law
any junction is a point of no loss nor no creation of charge; in = out
electric fields
regions around charged objects where electric forces can be exerted on another charged object
(electrostatically charged objects exert forces upon one another)
current
flow rate of charge
conventional current measures flow of positive charge (to negative terminal)
direct current
net charge always flowing in one direction (generally safer); batteries
alternating current
oscillating, or repeatedly alternating direction of charge flow, with no net movement of charged particles (e.g. cars, power supplies) → less safe
electric circuit
system that provides a complete path through which electricity travels
voltage
measure of electric potential difference (change in potential energy per unit charge between two defined points in the circuit)
when electrons clustered due to unequal distribution of charge, they have the potential to distribute the charge evenly by moving
work
total amount of energy required to move a certain quantity of charge (q) from one point to an another, in order to have a certain potential difference (V)
power
rate at which energy is transformed by circuit component
resistance
extent of which a particular material impedes the flow of electrons
caused due to collisions between free electrons and atoms/ions in the metal (smaller level, chemical micro properties)
larger properties that effect resistance
resistivity of material
length of wire (longer wire ⇒ more resistance)
cross-sectional area (thicker wire ⇒ less resistance); narrower space so more collisions
higher temperature ⇒ more kinetic energy ⇒ more collisions
bulbs in parallel vs series?
parallel brighter than in series
lower total resistance, so greater current, and thus greater power
resistance of ammeters
must be very LOW
majority of current flows through ammeter ⇒ accurately measure total current
resisters of voltmeters
must be very HIGH
if there was low resistance, voltmeter would start acting like a load itself and draw current from source, changing current experienced by actual load (so voltage)
otherwise, draws very low amount of current so load current approximately same
short circuit
electrical circuit that allows a current to travel along an unintended path with no, or very low, electrical resistance
low resistance ⇒ high current (electricity flowing through path of least resistance) ⇒ significant amounts of energy dissipated in looping wire ⇒ heats up lots
internal resistance
the opposition offered by materials of the battery cell itself, to the flow of electric current
factors affecting internal resistance
temperature
electronic resistance
ionic resistance
usage
how does temperature affect internal resistance
increased temperature ⇒ increased thermal agitation of metallic ions (greater kinetic energy) ⇒ conductor ions vibrate rapidly ⇒ increased collisions ⇒ inhibits free flow of electrons through substance ⇒ increased resistance
increased current passing through emf source heats it up (friction)
how does electronic resistance affect internal resistance
resistance of actual materials making the battery, such as metal caps, capacitor plating
how does ionic resistance affect internal resistance
by-products produced by redox reactions have a higher resistance than original reactants, and as reaction goes through multiple cycles, battery accumulates more high resistance substances within (increased r)
build up of mostly charged by-products in electrochemical cells increase the viscosity of electrolyte solutions, polarising the cell => greater frictional resistance and electrostatic repulsion => causes ion mobility to decrease, so greater resistance
how does usage affect internal resistance
usage increases ⇒ corrosion of metal current carriers ⇒ corroded particles offer additional resistance to flow of electron current ⇒ increased resistance
usage increases ⇒ consumes more components of electrolytes ⇒ decreasing concentration of charge carriers, increasing concentration of by-products ⇒ decreasing ion mobility and electrolyte conductivity ⇒ increased resistance
electromotive force
the energy provided per coulomb of charge, and is the maximum voltage that can be developed by a battery when there is zero external and internal resistance
TOTAL VOLTAGE DROP
