current electricity Flashcards by aleena sajan

complete the sentence(cts):

whn e move…

we say tht an electric current is produced

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definition of conventional current

the direction opposite to the flow of e, +ve to -ve terminal

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definition of electron flow

flow of current frm -ve to +ve:
this is because the electrons tht make up electric current is actly repelled by the -vely charged terminal n attracted to the +vely charged terminal

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definition of electric current

rate of flow of electric charge (through a given cross-section of a conductor)

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formula for electric current

I = Q/t

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what is 1Ampere?

1 apmere is the electric current produced whn 1 coulomb of charge passes thru a point in a conductor in 1second

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ampere is measred w?

ammeter connected in series-> used to measure the strength of an electric current in an electric circuit

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what does a power source do?

drive the electric charge arnd the circuit

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what does a load do?

conv ee to othr forms of energy to perform a function

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what does a conductor do?

connect the components

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what does a switch do?

open or close the circuit

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definition of closed circuit

one whr thr is an unbroken conducting path round in which charge can flow continuously

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definition of open circuit

a circuit in which thr is a brk at one or more points in the conducting path so tht thr is no current anywhere in te circuit:
why does this occur?
lose connection or missing/broken wires

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definition of short circuit

a circuit acts as a bypass for the electric current by providing an easier or shorter path for it to flow arnd
whn the circuit is closed but the bulb is still unlit bcos thr is an alternative path of negligible resistance(bare wire) for the current to flow thru, so the current will not flow thru bulb-> bulb wont light up

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definiton of electromotive force(emf)

emf of an electrical energy source is the work done by the source in driving a unit charge arnd a complete circuit

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formula for emf

emf= W/Q

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whn cells r arranged in series, the emf is

the sum of all the emfs of the cells(bigger than the biggest value of emf)

whn cells r arranged in parallel, the emf is

= to tht of a single cell

emf is measured by?

connecting a voltmeter in parallel

definition of potential difference

the pd across a component in an electric circuit is the work done to drive a unit charge THROUGH A COMPONENT!

formula for pd

V=W/Q

what happens whn thrs no pd?

charges will not move & thr will b no current flow

whn moving to highr pd to lower pd…(complete the sentence)

ee is conv to light or heat energy

pd is measured by?

connecting voltmeter in parallel

sum of emf in all the cells = to

sum of p.d across all the components in the circuit

definition of resistance

(R) of a component is the RATIO of the P.D., V across it to the CURRENT, I flowing through it

formula for R

R=V/I

cts: for a given pd, the increase in R...

the decrease in current passing thru

definition of resistors

is a conductor in a circuit tht is used to control the size of the current flowing in a circuit

variable resistor(rheostat):

has a R tht can b varied n can b used to vary the amt of current flowing thru the circuit

fixed resistors

has a R of a fixed value

how to measure R?

circuit components, other than resistors also have R so we can measure thm by measuring the I flowing thru the circuit n the pd across thm

state Ohm's law

Ohm's law states tht the current passing thru a metallic conductor is DIRECTLY PROPORTIONAL to the pd across it, provided tht othr physical conditions such as temp remain constant

formula for Ohm's law:

V/I=R=constant

graph of ohmic conductors

ohmic conductors-> conductors tht obey ohm's law straight line tht passes thru origin, constant gradient= inverse of the R of conductor the R of metallic conductors, ohmic or not generally increases w temp there is a solid line in the -ve region as well incase the voltmeter is connected wrongly(black to +ve n red to -ve)

graph for non-ohmic conductors, & eg of thm

non-ohmic conductors-> do not obey ohm's law, the current flowing thru non-ohmic conductors does not increase proportionally w pd so R may vary eg. Filament Lamp which convs ee to light n heat energy so as current increase the device generates more heat so temp increases and so resistance increases so graph shows tht R increases w temp but it increases in a decreasing rate Semiconductor diode: device tht allows current to flow in 1 direction only so whn pd is applied in the reverse direction-> thr is almost NO current flow which shows tht R is vry high in the opposite direction n in forward direction-> graph shows tht whn pd is applied, the current flow is relatively huge so R is low in forward direction

definition of light emitting diode

emits light whn current flows thru in a certain direction

resistivity

beside temp, R of a conductor also depends on: 1. its length,l 2. its cross-sectional area, A(or thickness) 3. the type of material it is made of

relationship btwn R n A

as A increases, R decreases proportionally

relationship btwn R n l

as l increases, R increases proportionally

formula relating R to A n L

R = p(ohmmetre) x L/A

materials w lower resistivities

better conductors of electricity