electricity junior cert science

Currents

a flow of electrical charge

Conductor

Anything that allows electricity to pass through it eg spatula, nail

unit for current

amp

Voltage

the potential difference between 2 sides of a circuit

Resistance

the ability of certain substances to reduce/ slow the flow of electric charge

Insulator

Anything that does not allow electricity to pass through it eg plastic dropper

symbol for resistance

R

Ohm's Law

as voltage increases, current increases; as resistance increases, current decreases

Forward Bias

The current will flow and the bulb will light

Reverse Bias

the current will be stopped and the bulb will not light

symbol for current

A

instrument for current

ammeter

unit for voltage

volt

symbol for voltage

V

instrument for voltage

voltmeter

instrument for resistance

ohmmeter

formula for resistance

V/I

unit for resistance

ohm

ohms law

voltage=current x resistance

series circuit

when the components eg bulb are connected one after the other in a row

observations of a series circuit

as more components are added all components get weaker because components are sharing current

if one component fails all other components fail too because a gap in the circuit means electricity cant flow

advantage of a series circuit

cheaper

disadvantage of a series circuit

when one component fails all fail

use of a series circuit

fairy lights

parallel circuit

when the components are connected side by side

observations of a parrallel circuit

as more components are added all components stay the same strength because components arent sharing current

if one component fails it doesnt affect the other components because there is no gap in the circuit

advantage of a parrallel circuit

if one fails the other components dont

disadvantage of a parrallel circuit

more expensive

use of parrallel circuits

car head lights

the different types of current

direct current

alternate current

direct current

current that flows in one direction only eg battery

alternate current

current that changes direction eg electricity mains( socket)

used to convert a.c. to d.c.

diode

the rate at which work is done work is converting energy

power

unit for power

watt

symbol for power

W

formula for power

power=voltage x current

use of a diode

used as a rectifier in appliances with a motor eg dishwasher it allows current to flow in one directions only

LED

light-emmitting diode

how to set up an LED in a circuit

must be forward biased

must be connected in series with a resistor to reduce current as LEDs can only tolerate a small current

use of a LED

as a diode it converts a.c. to d.c. and it provides light eg christmas lights

LDR

light dependent resistor

how a LDR works in a circuit

when light is strong resistance of LDR decreases so current increases so bulb is bright

when light is dim or in darkness resistance of LDR increases so current decreases so bulb is dim/off

use of LDR

auto control for flash on a camera or street lights turning on/off