Electrcity Flashcards
Circuit calculation steps
1: Work out total resistance using Rₜ = R₁ + R₂ and 1/Rₜ = 1/R₁ + 1/R₂
2: Work out total current V=IR
3: Use kirchhoff’s laws to work out volatge
Branches: Iₐ = I x R₈/Rₐ + R₈ and I₈ = I x Rₐ/Rₐ+R₈
Potential Divider equation
Vₒᵤₜ = R₂ x Vᵢₙ/R₁ + R₂
Define electric current
The rate of flow of charge and current
Current = charge/time
Define potential difference
The work done when one coulomb of charge is moved between two points in a circuit
PD = work done / charge
Define resistance
The ratio of the voltage across a component to the current flowing through it
resistance = voltage / current
What are the equations for electrical energy
E = ItV E = Pt
State Ohms law
The current flowing through a metallic conductor is directly proportional to the potential difference applied across it at constant temperature
What does the gradient of an I-V graph represent
1 divided by the resistance
Define resistivity
A measure of how easily a material conducts electricty
What is a superconductor
A material that has 0 resistivity below a certain temperature
What is the unit of resistivity
Ωm
How does a LDR work?
A light dependent resistors resistance changes based on light intensity. As the light intensity increases resistance decreases
How does a thermistor work
Resistance changes based on temperature. As the temp increases resistance decreases
What are the rules for a series circuit
Current is the same and voltage is split
What are the rules for parallel circuits
Current is shared and voltage is the same
What does Kirchoffs first law state
The total current into a junction is equal to the total current out of a junction
What does Kirchoffs second law state
The sum of EMFs around the loop is equal to the sum of the potential drops around the loop
Resistance in series
RT = R1 + R2
Resistance in parallel
1/RT = 1/R1 + 1/R2
What is a potential divider
Consists of two or more resistors in series and with a source of fixed potential difference (to produce aa
required PD)
How does a potential divider work
A potential divider uses resistors to dissipate energy and therefore reduce the work done per unit charge or the voltage output
Examples of potential dividers
Light dimmers and volume control
Define electromotive force (EMF)
The amount of energy transferred by a cell per unit charge that passes through it
What is internal resistance
The loss of potential energy per unit charge in the source when a current passes through it
