Electricity Flashcards
(53 cards)
Current (I) definition
A measure of the flow of electrons around the circuit.
Measured in amperes, amps (A) = coulombs per second
Coulomb definition
Amount of electricity that 1 amps of current carries in one second.
Potential Difference (V) definition
Measured in volts (voltage)
Force driving the flow of electrons - measure of how much energy is transferred between two points in a circuit.
P.d. across a power supply or battery is the energy transferred to each coulomb of charge that passes through it.
Resistance (R) definition
Everything that resists or opposes the flow of electrons. Measured in ohms.
Which way does current flow?
Whereas conventional current assumes that current always flows from the positive to the negative.
OHM’s LAW:
V =
voltage =
I x R
current x resistance
OHM’S LAW: when resistance does not change, as we increase voltage, current should increase…
proportionally.
All circuits are a closed loop that include:
- a power source e.g. cell
- something for electrons to flow through e.g. wire
Components: Electrical power
cell; battery
Components: controls the flow of electricity
switch
Components: Filament Lamp
Small bulb - was banned as it’s temperature rises to dangerous temperatures/ inefficient as heat energy is wasted.
Contains metal filament that dramatically increases to high temperatures so much so that it glows, producing light.
Components: Fuses
break is too much current flows through, breaking the circuit - thus protects wires and other components from getting damaged if a faulty appliance has caused too much flow of current.
Components: Diode
only allows current to flow in one direction.
Component: LED
light-emmitting diode
light emmitted when current flows through in the forward direction - light is useful energy and no thermal energy is wasted - efficient
Components: to measure
Ammeter - current/ connected in series with component
Voltmeter - voltage/ connected in parallel
Components: Resistors: LDR
light-dependent resistor - resistance depends on the intensity of light
Components: Resistors: Fixed resistor
fixed to supply a certain number of ohms worth of resistance ALWAYS
Components: Resistors: Variable resistor
can be manually modified to desired amount of resistance
Components: Resistors: Thermistor
resistance depends on temperature
IV graphs fixed answers:
straight line through the normal when “assuming temperature stays constant” and the circuit is made with only wires and fixed resistors
voltage and current increase proportionally thus ohm’s law is obeyed.
IV graphs fixed answers: filament lamp - line through the normal - s shape
The more it heats up, the greater the resistance, so the curve gets less steep as resistance increases - less current can flow per unit of p.d. at high temperatures.
IV graphs fixed answers: Diode - curve when p.d is positive
only allows current to flow in one direction which is why they only show a current when the p.d is positive.
Why does an increase in temperature increase the resistance of wires and fixed resistors?
As temperature increases, the metal ions of the wire vibrate faster which makes it harder for electrons to pass along the wire (resistance increases).
Charge (Q) =
current x time
I x t
