# Science - Physics - Electricity - P2 Flashcards

what is the circuit symbol for a cell ?

+ I

-I l-

what is the circuit symbol for a battery ?

+I l l

-I l ….l l-

what is the circuit symbol for an open switch ?

-./ ._

what is the circuit symbol for a closed switch ?

-.–.-

what is the circuit symbol for a filament lamp or bulb ?

-x-

what is the circuit symbol for an ammeter ?

-A-

what is the circuit symbol for a voltmeter ?

-V-

what is the circuit symbol for a resistor ?

rectangle with lines either side

what is the circuit symbol for a variable resistor ?

same symbol as a normal resistor, but with an arrow through it

what is the circuit symbol for a fuse ?

rectangle with a line going through it

what is the circuit symbol for a thermistor ?

same as a normal resistor but with a line going halfway across under it, then diagonal up

what is the circuit symbol for a diode ?

circle with a triangle and a line inside of it, with a line going through the middle

what is the circuit symbol for a LED (light emitting diode) ?

same symbol as diode, but with 2 arrows diagonally above it pointing upwards

what is the circuit symbol for an LDR ( light dependant resistor) ?

a circle with the resistor symbol in it, and 2 diagonal arrows above it pointing down

what does LED stand for ?

light emitting diode

what does LDR stand for ?

light dependant resistor

what does a voltmeter measure ?

potential difference

what does an ammeter measure ?

current

how is a voltmeter connected in a circuit ?

across a component - in parallel

how is an ammeter connected in a circuit ?

in line with a component - in series

what is potential difference ?

the driving force that pushes electric charge around a circuit

what is an electric current ?

a flow of electric charge

does current flows from positive to negative or negative to positive around a circuit ?

positive to negative

which terminal line in cells is positive and which is negative ?

longer terminal line - positive

shorter terminal line - negative

what affects the rate of flow of charge ?

the size of the current

what is the rate of flow of charge measured in ?

amperes

how do you calculate rate of charge flow ?

Q = I X T

Q- charge flow

I - current

T - time

does more charge pass around a circuit when a bigger or smaller current flows ?

a bigger current

a battery charger passes a current of 2.5 through a cell over 4 hours, how much charge does the charger transfer to a cell altogether ?

I = 2.5 T=4 x 60 x 60s = 14 400 s

Q = IT = 2.5 x 14 400 = 36 000 C

what is needed for a current to flow in a circuit ?

potential difference

how is a circuit complete ?

if you can follow a wire from one end of the battery, through any components to the other end of the battery

what is resistance ?

anything in the circuit which reduces the flow of current

what is resistance measured in ?

ohms

what does the current flowing through a component depend on ?

resistance of the component, and the potential difference across it

the greater resistance, the ……. the current that flows ?

smaller

how do you calculate resistance ?

V= IR

V- potential difference

I- current

R- resistance

a voltmeter reads 6.0 v and a resistor has a resistance of 4.0, what is the current ?

rearrange the formula to I = V/R

I = V/R = 6.0/4.0 = 1.5 A

does the resistance of an ohmic conductor change with the current ?

no

the resistance of an ohmic conductor is directly proportional to what ?

the potential difference across it

what is an ohmic conductor ?

a conductor with resistance that is constant at a constant temperature

name 2 factors that affect resistors

- whether the components are in series or parallel
- the length of the wire in a circuit

as the length of the wire increases, what happens to the resistance ?

it increases

what do I - V characteristics show ?

how the current varies as potential difference changes across the component

what happens to the resistance of non-linear components ?

the resistance changes depending on the current

how do you find a components I-V characteristic?

vary the resistance of the variable resistor

this alters current flowing through the circuit and the potential difference across the component

explain the resistance of a filament lamp

when electrical charge flows through a filament lamp it transfers some energy to thermal so the lamp heats up and glows, the higher the temperature, the higher the resistance so as the lamp heats up more the resistance increases so less current can flow

explain the resistance in a diode

a diode is a component that only lets current flow through it in 1 direction, so the resistance depends on the direction the current is flowing, the diode will happily let the current flow one way, but will have a very high resistance if the current is reversed

what are series circuits ?

different components connected in a line, end to end, between the positive and negative ends of the power supply, except for voltmeters which are always connected across a component

if you remove or disconnect 1 component in a series circuit, what happens ?

the circuit is broken, and they all stop

what are series circuits used for ?

- to measure quantities
- test components

how do you calculate potential difference in a series circuit ?

the sum of the potential differences of all the batteries in the circuit

the potential difference around a series circuit is always what ?

equal

in a series circuit, the current is what ?

the same in all parts of the circuit

what is the size of the current determined by in a series circuit ?

the total potential difference of the cells and the total resistance of the circuit

in a series circuit, how do you calculate the total resistance ?

add up all the resistances

in a series circuit, the bigger the resistance of a component, the bigger the what ?

its share of the total potential difference

which circuits are generally more useful, series or parallel ?

parallel

what is a parallel circuit ?

components each have their own branch in a circuit connected to the positive and negative terminals, except ammeters which are always in series.

if you disconnect one branch of components in a parallel circuit, what happens to the other branches ?

it won’t affect them as current can still flow in a complete loop from one end of the power supply to the other branches that are still connected

where are parallel circuits used ?

in household electrics

what is the potential difference like in parallel circuits ?

it is the same across all components connected in parallel

why is parallel connection useful in cars ?

- everything can be turned on and off separately
- everything as the full potential difference of the battery across it so you can have music on full blast without it having much effect on the brightness of your lights

what is current like in parallel circuits ?

the total current flowing around the circuit is equal to the total of all the currents going through the seprate branches

can the current be different in the mini branches in parallel circuits ?

yes

is the current the same thought each mini branch in a parallel circuit ?

yes

how do you calculate the total current in the parallel circuit ?

add up the total currents from each branch