Electricity and electrostatics Flashcards
what do conductors do
they allow charged particles to move through it. The delocalised sea of electrons in a metal wire are free to move
what do cells/batteries do
more electrons will move towards the positive terminal. there is a net flow of current through the wire
which way do electrons flow
they flow from positive to negative terminal(syllabus of iGCSE) but actually they flow from the negative terminal to the positive terminal because electrons are negatively charged
definition of charge
Charge is a property of a body which experiences a force in an electric field
definition of current
rate of flow of charge
what is the equation linking charge, current and time
Q = I x T (charge (coulombs[c]) = current(amperes[A]) x time(seconds[s]))
what does a cell do
gives energy to the elctrons
what does a wire do
carries current
what do bulbs do
converts electrical energy to light
what do ammeters do
measures the current
what do resistors do
opposes flow of electrons
how does current work in series
current stays the same everywhere in series
how does the current in parallel circuits work
the current will go into paths proportional to the resistance following the rule V = IR
what is voltage
energy/charge
how does voltage work in series circuit
the total voltage will be split proportionally to the resistance of the components following the rule V = IR (if the resistance increases, the voltage will also increase
how does voltage work in parallel
the voltage will be the same everywhere, unless there are multiple components in a single path
how many joules of energy is given to each coulomb of charge that passes through the cell if the cell is 1.5V?
1.5J of energy
formula linking voltage, energy and charge
V = E(J)/Q(C)
how can you measure voltage
measure voltage using a voltmeter which is connected in parallel with the component we are interested in
rules for resistance in series
R1 + R2 = RT(total)
rules for resistance in parallel
1/R1 + 1R2 = 1/RT
why does resistant increase in an filament Light bulb
-The current increases, which leads to the the electrons transferring more KE to the metal ions
-The ions vibrate more, increasing the chance of electrons scattering, so the resistance increases
what name is given to a light bulb that doesnt increase resistance as the current increases
ohmic
what is a diode
a semi-conductcor device that only allow current to flow one way
what is a thermistor
The resistance of a thermistor depends on its temperature. At low temperatures, the thermistor has a high resistance. As the temperature increases, the resistance decreases.
uses of a thermistor
A thermistor can be used in thermostats or heat activated fire alarms.
what is an LDR
The resistance of a LDR depends on light intensity. At low light levels, the LDR has a high resistance. As the light intensity increases, the resistance decreases.
uses of an LDR
A LDR can be used as a sensor in cameras or automatic lights that come on when it gets dark.
what are diodes used for
converting alternating current into direct current
why does the resistance increase of a filament lamp as the voltage increases?
-lamp heats up due to higher voltage
-ions vibrate more
-greater chance of electron collisions
-resistance increases
memorise symbols
-google it
why should domestic lighting be in a parallel circuit
-allows lights to work independently
-they all get the same mains voltage (230V)
-so different areas can get different light intensities
electrical conductors
conducts charge easily
electrical insulators
do not conduct charge very well so current cannot flow
what is a static charge
charge which builds up in one space and is not free to move
what causes sparks
-when an electrical charge builds up on an isolated object, the voltage between the object and the earth increases
-if the voltage gets large enough, electrons can jump across the gap between the charged object and earth/earthed object, causing a spark
how is static electricity helpful in an inkjet printer
-droplets of ink are forced out of a fine nozzle, and are then given an electrical charge
-droplets are deflected as they pass between two metal plates. A voltage is given to the plates, one is -ve, one is +ve
-droplets are attracted to the plate of the opposite charge and are repelled from the plate with the same charge
-size and direction of the voltage across each plate changes so each droplet is deflected to hit a different place on the paper
how is static electricity helpful for photocopiers
-image plate is +vely charged. An image of what you are copying is projected onto it.
-whiter bits of what you are copying make light fall on the plate and the charge leaks away there
-charged bits attract negatively charged black powder, which is then transferred onto positively charged paper
-paper is heated so the powder sticks
