Electricity Flashcards
What is effective resistance
the measure of the resistance of all the resistors throughout the circuit.
Current vs voltage graph for a wire
Current vs voltage graph for a lamp
Current vs voltage graph for a thermistor
Current vs voltage graph for a diode
Diode and light emitting diode diagram
Resistor, variable resistor, thermistor and light dependant resistor diagrams
Heater diagram
Electric motor diagram
What is an ohmic conductor
A conductor that obeys Ohm’s Law
What is a LDR also known as and when is its resistance highest?
Photocell - when the light intensity is lowest
Graphs for a capacitor (charge, voltage and current)
What is the electromotive force
The potential difference across the terminals of a battery when no current flows
What are lost volts
The voltage used to overcome the internal resistance of the battery
What is the terminal voltage
The voltage delivered to the load resistance in the circuit (the p.d when no current flows; the terminal voltage is the p.d when current flows)
Equation linking charge current and time taken for a capacitor to reach the charge
Q=I x t
describe in terms of electron flow what is happening when a capacitor charges up
Capacitors are charged by a power supply (e.g., a battery)
One plate of the capacitor is connected to the positive terminal of the power supply
The positive terminal ‘pulls’ electrons from this plate
Hence the plate nearest the positive terminal becomes positively charged
These electrons travel around the circuit and are pushed from the negative terminal of the power supply
The negative terminal ‘pushes’ electrons onto the other plate
Hence the plate nearest the negative terminal becomes negatively charged
As the negative charge builds up, fewer electrons are pushed onto the plate due to electrostatic repulsion from the electrons already on the plate
When no more electrons can be pushed onto the negative plate, the charging stops
How are capacitors used?
What is the time constant of capacitance
Time taken for charge or potential difference to increase by 63% OR fall by 37%
Capacitance def
Charge stored per unit potential difference
Graphical method for measuring time constant of capacitance
Mathematical method for calculating the time constant of capacitance
What is one farad equal to?
1 coulomb per volt (C/V)
What is the energy store in a capacitor
- Electric potential energy
- it is the energy stored in the electric field formed by the oppositely charged plates
Calculating the energy stored in a capacitor graphically
Dielectric material def
What do the components of this equation mean?
What do the components of this equation mean?
What happens when a dielectric is placed between the plates of a capacitor?
The individual molecules become polarised
Do dielectric materials have different permitivities?
Yes - this is the ability for the dielectric to hold an electrical charge. This is shown by the letter E
EMF definition
The amount of chemical energy converted to electrical energy per coulomb of charge (C) when passing through a power supply
equal to the terminal potential difference when no current flows.
EMF Equation
is EMF a force
It is not actually a force, and is measured in volts
how is emf measured
what is terminal potential difference
the potential difference across the terminals of a cell
If there was no internal resistance, the terminal p.d would be equal to the e.m.f
Since a cell has internal resistance, the terminal p.d is always lower than the e.m.f
describe what lost volts are and why they exist
- In a closed circuit, current flows through a cell and a potential difference develops across the internal resistance
- Since resistance opposes current, this reduces the energy per unit charge (voltage) available to the rest of the external circuit
- This difference is called the ‘lost volts’
- Lost volts is usually represented by little v
lost volts def
The work done per unit charge / coulomb to overcome the internal resistance / resistance inside the battery (when current flows)
internal resistance def
The resistance of the materials within the battery
