topic test - electricity

Question 1

electrostatics

Answer 1

study of electrical charges at rest, forces existing between charges, and the electric fields associated with them

Question 2

electric charge

Answer 2

extent to which matter has greater or fewer electrons than protons

Question 3

law of electric charges

Answer 3

“like charges repel, opposite charges attract”

Question 4

electric force

Answer 4

forces between electrostatically charged objects, dependent on:
- amount of charge
- distance between charges

Question 5

static electricity

Answer 5

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

Question 6

charge by friction

Answer 6

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

Question 7

charge by conduction

Answer 7

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

Question 8

charge by induction

Answer 8

electron transfer without direct contact (induces charge, then forces of attraction and repulsion by electric fields)

must be for conductors only

Question 9

inducing positive charge

Answer 9

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

Question 10

inducing negative charge

Answer 10

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

Question 11

grounding

Answer 11

connected to earth by wire to neutralise charged conductors, due to electrons flowing into earth

Question 12

conductors

Answer 12

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

Question 13

insulators

Answer 13

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

Question 14

law of conservation of charge

Answer 14

net charge of isolated system remains constant

Question 15

kirchoff’s law

Answer 15

any junction is a point of no loss nor no creation of charge; in = out

Question 16

electric fields

Answer 16

regions around charged objects where electric forces can be exerted on another charged object

(electrostatically charged objects exert forces upon one another)

Question 17

current

Answer 17

flow rate of charge

conventional current measures flow of positive charge (to negative terminal)

Question 18

direct current

Answer 18

net charge always flowing in one direction (generally safer); batteries

Question 19

alternating current

Answer 19

oscillating, or repeatedly alternating direction of charge flow, with no net movement of charged particles (e.g. cars, power supplies) → less safe

Question 20

electric circuit

Answer 20

system that provides a complete path through which electricity travels

Question 21

voltage

Answer 21

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

Question 22

work

Answer 22

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)

Question 23

power

Answer 23

rate at which energy is transformed by circuit component

Question 24

resistance

Answer 24

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)

Question 25

larger properties that effect resistance

Answer 25

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

Question 26

bulbs in parallel vs series?

Answer 26

parallel brighter than in series

lower total resistance, so greater current, and thus greater power

Question 27

resistance of ammeters

Answer 27

must be very LOW

majority of current flows through ammeter ⇒ accurately measure total current

Question 28

resisters of voltmeters

Answer 28

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

Question 29

short circuit

Answer 29

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

Question 30

internal resistance

Answer 30

the opposition offered by materials of the battery cell itself, to the flow of electric current

Question 31

factors affecting internal resistance

Answer 31

temperature

electronic resistance

ionic resistance

usage

Question 32

how does temperature affect internal resistance

Answer 32

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)

Question 33

how does electronic resistance affect internal resistance

Answer 33

resistance of actual materials making the battery, such as metal caps, capacitor plating

Question 34

how does ionic resistance affect internal resistance

Answer 34

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

Question 35

how does usage affect internal resistance

Answer 35

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

Question 36

electromotive force

Answer 36

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