P2: Electricity WIP [No triple yet] Flashcards
What is electricity?
Electricity is the movement of charge. It can occur in two ways
> Through the flow of electrons
> Through the flow of ions (such as in batteries & electrolysis)
What is charge?
Charge is a scalar quantity that measures the proportion of overall charge flow of a circuit
> It is measured in Coulombs
What is current?
Current is a measure of the rate of charge flow along a circuit
> It is measured in Amperes, a unit similar to watts in that it is an amount of coulombs per second
> Current also moves from the negative to the positive
> Conventional current flow, the theory originally believed, put forth the idea that current flowed from positive to negative
+ Current is measured using an Ammeter, connected in series
What is Potential Difference?
Potential difference (Voltage) is the difference in energy before and after the battery in a circuit, and acts as the driving force that moves energy along a circuit
> Voltage can also be described this way: When a current passes through a component, it loses energy to the component, and comes out the other side with a different energy value. The difference in energy values is the voltage
> It is measured in Volts
+ P.D. is measured with a Voltmeter, connected in parallel across a component
What is resistance?
Resistance is the force opposing the transfer of energy electrically, and is a measure of how difficult it is for current to flow through a component
> Resistance comes from stationary protons that the electrons collide with
> It is measured in Ohms
What correlations are there between Current, Charge, Resistance, Potential difference & other forces/energies?
+ When voltage increases, so does current (Greater push forces more energy & charge per second)
+ The current through a component is dependant on the resistance & voltage across it
> The greater the resistance, the smaller the current for the given potential difference
What is the equation of charge?
Charge = Current x Time Coulombs = Amperes (Coulombs/second) x Seconds
What are the base circuit symbols required for GCSE?
+ Switch (Open/Closed) : Opens/closes a circuit
+ Cell : Produces a Voltage
+ Battery : Multiple Cells connected
+ Filament Lamp : Produces light
+ Fuse : Prevents power surges from damaging electronics
+ Diode : Allows current to flow in one direction alone
+ Light-emitting diode (LED) : Emits light
+ Resistor (Ohmic) : Produces a resistance
+ Variable Resistor : produces a controllable resistance
+ Thermistor : Has a variable resistance dependent on temperature
+ Light dependent resistor (LDR) : Has a variable resistance dependent on Light Intensity
What is the difference between a series & parallel circuit?
A Series circuit consists of a singular loop, whereas a Parallel circuit has multiple branches & diversions
How can potential difference be calculated?
Potential Difference (Voltage) = Current x Resistance Volts = Amperes x Ohms (Ω)
Note: This equation is also known as Ohm’s law
What factors affect the resistance in a circuit?
+ The length of a wire: electrons have a greater probability of colliding with ions in a longer wire [High Length = High Resistance]
+ The thickness of a wire: A thicker wire means there are fewer collisions per electron
+ The material of the wire: Different materials have different electrical conductivities
+ The temperature of the wire: A hotter wire has a greater resistance, as the ions vibrate more intensely & are more likely to collide with moving electrons
What is an Ohmic conductor?
+ An ohmic conductor is a resistor that’s resistance does not change no matter the current flowing through it
> They adhere to Ohm’s law (The current through an ohmic conductor is directly proportional to the current through the conductor)
+ On an I-V graph, ohmic conductors will produce a straight line through the origin with a positive gradient
What do the graphs of non-Ohmic conductors look like?
+ Current & voltage across a non-ohmic conductor are not directly proportional
> In a filament bulb, resistance increases with the current as the filament warms
> In a diode, resistance is high in one direction and low in the other
What is the relationship between resistance & light/temperature in LDRs & Thermistors?
+ They are inversely proportional
> In a thermistor, a high temperature means a low resistance
> Therefore, they can be used in thermostats
> In an LDR, a high light intensity means a low resistance
> Thus they have good applications in automatic night lamps
What are the rules for current, potential difference & resistance in series circuits?
+ At every point in the circuit, current is the same
+ Potential difference across the whole circuit is split between components, dependent on their resistances
+ The total resistance of the circuit is the sum of all the components’ resistances
