P4 electric circuits

atom charge

none because has equal numbers of +ive protons and -tive electrons

atom charge when electrons removed/added

becomes positively charged when removed

becomes negatively charged when added

insulating materials

become charged when rubbed with other insulating material because electrons are transferred from one material to another

positive charges do NOT usually transfer between materials

electric charge measured in coulombs

electric field

around a charged object

electrostatic force

experienced when a charged object is placed in electric field of another charged object

THIS MEANS two charged objects exert a non-contact force on each other

what happens when electrostatic force..

like charges repel each other

opposite charges attract each other

electric field and force between two charged objects

gets stronger

distance between them decrease

strong electrostatic field

electrons in air molecules strongly attract the +tive charged object and if field is strong enough, electrons pulled away from air molecules causing flow of electrons between the objects (a spark)

electric field diagram

drawn with field lines to show direction of force that a small positive charge would experience when placed in electrical field

drawing electric field diagram

• field lines meet the surface of charged object at 90°

• arrows always point away from +tive charge and towards -tive charge

electric current

when charge flows

the charge in an electric circuit is carried by electrons

unit of current

AMPERE (A)

1 ampere=1 coulomb of charge flow per second

conventional current

in circuit diagrams when charge flows from the positive terminal of a cell or battery to the negative terminal

single closed loop

current has the same value at any point in the circuit

metals

good conductors of electricity because they contain delocalised electrons which are free to flow through the structure

potential difference

measure of how much energy is transferred between two points in a circuit (V)

• across a component is the work done on it by each coulomb of charge that passes through it

• across a power supply/battery energy transferred to each coulomb of charge that passes through it

resistance

opposition in an electrical component to the movement of electrical charge through it. Resistance is measured in ohms.

series

one loop; all electrons in that loop form one current

static

electric charge that accumulates on an insulated object

what causes resistance

when electrons move through a circuit they collide w ions and atoms of the wires and components in te circuit

long vs short wire

long has more resistance bc electrons collide w more ions as they pass through

resistance of electrical component equation

PD (V)= current(A) x resistance (Ω)

ohmic conductor graph

current directly proportional to PD in an ohmic conductor at a constant temp

resistance constant

diode graph

current through diode only flows in one direction(forward direction)

needs minimum voltage before any current will flow

filament lamp graph

more current through filament=temp increase

atoms in wire vibrate more, collide more w electrons flowing through

resistance increase as temp increase

resistance of ohmic conductor

calculate gradient at that point and take inverse

resistance =

1

---

gradient

cell

electrical power supply

battery

main source of energy that provides a voltage which allows the current to flow through

switch

enables the flow of electricity to be turned on and off

bulb

fixed resistor

resistance that remains the same

variable resistor

resistance that is used in some dimmer switches and volume controls

fuse

in an appliance causes too much current to flowbreaks the circuit if a fault

diode

allows current to flow in one direction but not in the reverse direction

thermistor

temperature sensor

LED (light emitting diode)

transfer a greater proportion of electrical energy as light energy

LDR (light dependant resistor)

used to detect light levels

ammeter

measure the current flowing through a circuit

voltmeter

measure the potential difference (voltage) between two points in a circuit

series circuit

components are connected in a single loop

if one component stops working, the whole circuit stops working

components in a series circuit

components w a higher resistance will transfer a larger share of total PD because V=IR (and current is the same through all components)

parallel circuits

made up of two or more loops through which current can flow

if one branch of parallel stops working, other branches not affected

total resistance of 2 or more components in parallel

always less than smallest resistance of any branch bc adding a loop to the circuit provides another loop for the current to flow so more current can flow in total even though PD hasn’t changed.

adding more resistors to parallel

decreases total resistance of circuit