?Tuesday, October 09, 2007
Heidi blows a kiss to you, dearly, @12:02 PM!
ouh righty.
this post, yoo can nort read.
i feel bored studying science with silence.
so i`m gonna like type out and revise everything(:
i really really hope it`ll help me in getting an A.
topic:
electricity
(electric circuits)
sources of electricity
two main sources.
1.mains electricity.
> plugs of appliances are inserted to sockets.
> generated from power station
> dangerous
> can give electric shock
> produce large amount of energy
2.electric cells
> produce little amount of energy
> safe to use.
>comes in different voltages in portable forms
> used for portable devices
electric circuits
> electricity flow through electric current
> path, is called electric circuit.
closed circuit
> there has to be a complete path in the circuit without any gaps.
open circuit
> incomplete circuits.
> bulbs cannort light up.
an electrical energy flows only when there is:
a source ofelectrical energy and
a closed circuit.
circuit diagrams.
can`t be drawn here.-.-
switches.
open switch - don`t light up
close switch - light up.
conductors and insulators
conductors allow electricity to pass through.
insulators dont allow electricity to pass through.
conductors e.g copper iron aluminium
insulators e.g plastic wood rubber glass
series and parallel circuits
series- single path.
when one bulb fuses, the rest fuse.
current that flows through each component is the same.
parallel - divided into two or more branches.
when one fuses, the rest still works.
current divides and flows through each of the branches.
(current and voltage)
electic current
> flow of electrons in one direction in a circuit
electric cell gives energy to electrons and push them around the circuit.
from (-) terminal to (+) terminal.
measuring electric current
- ammeter to measure
SI unit: ampere(A)
1 A = 1000 mA
1 mA = 0.001 A
ammeter is always connected in series.
positive (red)
negative (black)
positive must be connected to positive part of the cell.
negative must be connected to negative part of the cell.
hold on, i`m like on MSN now,
so many people talking to me!
URGH.
currents of different size flow through different component.
voltage
- volmeter to measure
volateg is a measure of how much energy the electrons receive.
SI unit:volt(V)
voltmeter is always in parallel.
postive(red) connect to positive part of the cell.
negative(black) connect to negative terminal of the cell.
each cells have diff. voltage.
mains volatge is much greater, singapore-230V
connecting cells in series
as the no. of cells increse, the voltage increase too.
the voltage across all the cells is equal to the sum of the voltages of the individual cell.
(resistance)
greater the resistance, the lower the current.
copper have low resistance. used for connecting wires, allows electrons to flow easily.
silver have even lower resistance, but too expensive to be used.
nichrome has larger resistance than copper.
hence somtimes used to decrease current.
also known as resistance wires.
SI unit: ohm(Ω)
resistors
electrical component that is made specially to have a certain resistance.
resistors with fixed resistance, called fixed resistor.
common ones, e.g nichrome, high resistance.(made from carbon or metal)
mainly used to control current that flows.
variable resistor, also known as rheostat.
when resistance of rheostat change, current and resistance also change.
uses:
volume controls in radios are rheostats,
as the resistance control decreases, current in the loudspeakers increases which maes the sound louder.
dimmers in cinemas use rheostat to make lights brighter or dimmer.
the speed control of toy car is a rheostat.
as the resistance decreased, current increase, toy car goes faster.
resistors in parallel and series
in series circuit, the overall resistance increases as more resistors are added.(this is similar to increasing the length of a resistance wire in a circuit)
in parallel circuit, the overall resistance decreases as more resistors are added.
adding resistor in series,
increase resistance,
therefore, current and brightness of bulbs decreases.
adding resistors in parallel.
resistance decrease,
therefore current and brightness of bulb increases.
(effects of an electric current)
memorise!
the heating effect of an electric current
when an electric current flows through a wire, the wire heats up.
the energy changes as follows.
electrical energy ---> heat energy
the greater the resistance of the wire, the greater the amount of heat produced.
copper wire, low resistance, nort hot.
nichrome, high resistance, very hot,
heating effect is used in common electrical appliances.
(e.g) iron, kettle, hairdryer.
each of these appliances has a a heating "element" inside which inside which becomes hot when a current flows through.
still gort somemore.
tonight kay?
ouh wow. i took 3 hours for one thing.
omgawd heidi tay.CONCENTRATE.
i was doll making with esther
will post pictures next time
and fighting with leon.
credits: explore the world with SCIENCE DISCOVERY 2 ;pearson longman
When life begins with you,
