Electricity- electric change Flashcards
what is a component
a device in a circuit such as lamp
what is electric current
the flow of electrical charge
what is voltage or potential difference
the energy transferred per electron
what is resistance
- anything that slows the flow of electric charge down
charge equation
Q = I (Current) t (time)
what equation links current, voltage and resistance
V= IR
What does a diode do
allows current to flow in one direction only. Current will not flow in the other direction
what is a diode used for
to convert an alternating current into a direct current
what is a alternating current ac
an electric current that regularly changes size and direction
what is a direct current dc
an electric current that moves in one direction
what is electrical current
flow of electrons
how can we measure the current through a component
place an ammeter in series with that component
how can we measure voltage across a component
a voltmeter must be placed in parallel with that component
what is the equation linking voltage, charge and energy transferred
voltage = energy transferred/ charge
what is an electric insulator
a material that does not let electric current through it
examples of electric insulators
- plastic
- rubber
- glass
why can’t electric insulators conduct electricity
because they have no free electrons so no charges are free to move and carry charge
why can electric conductors conduct electricity
An electrical conductor has lots of charges that are free to move.
In a metal, the charges that are free to move are electrons.
The electric current through the metal is the flow of these free electrons.
what must voltmeters be connected in
parallel
what must ammeters be connected in
series
how do lengths of wires affect resistance
the longer a wire, the higher the resistance
what is a thermistor and its properties
a component where resistance changes with temperature
- resistance decreases as temperature increases
- high temps = low resistance
- low temps = high resistance
what is a LDR and its properties
a component where resistance changes with light intensity, increasing light intensity decreases resistance
- in dark conditions, resistance is high
- in light conditions, resistance is low
equation linking energy power and time
energy transferred = power x time
equation linking power, voltage and current
P = I x V.
We know V = IR, so power can also be calculated by:
P = I^2R
what makes current flow
the energy source ( battery etc)
what is ohms law
The current through an ohmic conductor is directly proportional to the potential difference across the resistor.
This means that the resistance remains constant as the current changes.
w What happens if we close the switch?
A current can flow through the circuit
what are diodes used for
to control the flow of current in circuits
examples of how ldrs are used
- to detect light
- to turn pff a phone when ur on a call
- in the light, the resistance of the LDR is very low, meaning it takes very little energy for the current to pass through the LDR
- because of this the pd across the ldr is very low
- because potential difference is shared between components in series, the pd across the lamp is large
- if the phone is held to a persons ear, the ldr is in darkness and the resistance of the ldr rises sharply. now it takes a great deal of energy for current to pass through the ldr so pd across it is very high
- meaning theres less electrical energy for the lamp
how are thermistors used
- in thermostats in computers to reduce them getting hot
- curcuit usually has a fan
- thermistor is connected in series to the cooling fan
- under cool conditions, the resistance of the thermistor is high, meaning it takes a lot of energy for the current to pass through thermistor
- because of that the pd across the thermistor is high and pd across the fan is small
- if computer gets hot, the resistance of thermistor falls, takes much less energy for the current to pass through thermistor
- this means pd across the thermistor is very low so more electrical energy is available for the fan
- this makes the pd of the fan very high so that it can be warmth
