Electricity Flashcards
What is the Symbol and Units of Charge?
Symbol: Q
Units: Coulombs (C)
What is the Charge of an Electron?
-1.6x10^-19 C
What is the definition of Current?
Rate of change of Charge
Or
The amount of charge flowing in one second
What is the Symbol and Units of Current?
Symbol: I
Units: Ampere (A which is Cs^-1)
What is Potential Difference?
The work done per coulomb of charge
What is the definition of Current as an equation?
Current = Charge/Time I = ΔQ/Δt
What is the Symbol and Units of Potential Difference?
Symbol: V
Units: Volts (V which is JC^-1)
What is the defintion of Potential Difference as an equation?
Potential Difference = Work Done/Charge
V = w/Q
What is an alternative name of Potential Difference?
Voltage
What is the definition of Resistance?
The ratio of p.d to current
What is the Symbol and Units of Ressistance?
Symbol: R
Units: Omhs (Ω which is VA^-1
How do you calculate the number of Electrons required to make a Charge?
Number of Electrons = Charge/Electron Charge
n = Q/e (n = 1.6x10^-19)
What equation links Power, Energy and Time?
Power = Energy/Time P = E/t
What equation is used to convert between kWh and J?
Joules = Kilowatt x Number of Seconds in a Hour J = kWa x 3600
What set of equations link Power, Potential Difference, Current and Ressistance?
Power = p.d x Current = Current² x Ressistance = p.d²/Ressistance P = VI = I²R = V²/R
What is an Ohmic Conductor?
A conductor where the p.d across it directly proportional to the current
What is the Operating Voltage of a Diode?
The p.d which the diode occupies
generaly about 7V
What happens to most Conductors when the temperature increases?
The resistance increases
Why does Resiatance increase with temperature?
Increased lattice vibration due to more energy
∴ elctrons find it harder to flow
∴ resistance increases
What is Superconductor?
A material that when at or beneath the resistance becomes Zero
(Not just close to Zero, But is Zero)
What is a use of Superconductors?
MRI scanners
conductors when a very large magnetic field is needed
What is a Semiconductor?
A materials whose resistance decreases as temperature increases
How does a Semiconductor work?
The temperature increase causes an increase in “free” electrons
∴ more charge is available
∴ resistance decreases
What is a Thermistor?
An electrical component that is based on semiconductors
Temp↑ cause Resistance↓
How is Current spread out in a Series Circuit?
Current is the same at all points within the circuit
How is p.d spread out in a Series Circuit?
It is the product of the current and the resistance of that component.
How is the total p.d of a Series Circuit calculated
V(total) = ΣV(components)
How is the total Resistance of a Series Circuit calculated?
R(total) = ΣR(compoents)
What is the Potential Divider equation?
V(1) / V(total) = R(1) / R(total)
How is the Current spread out in a Parallel Circuit?
Current in each branch is based of its resistance
How is the total Current in a Parallel Circuit calculated?
I(total) = Σ I (of each branch)
How is the total Resistance clalculated within a Parallel Circuit?
1/R(total) = 1/ΣR(of each branch)
How is p.d spread out within a Parallel Circuit?
p.d is the same across every branch of the circuit
What is a quick way of calculating the total Resistance of identical resistors in parallel?
Total Resistance = Resistance / Number of Resistors
R(total) = R/n
What is the Symbol and Units of Resistivity?
Symbol: ρ
Units: Ωm
What is the equation of Resistivity?
Resistivity = Resistance x Cross-Sectional Area / Length ρ = RA/L
What is the Symbol and Units of Electromotive Force?
Symbol: ε
Units: V
Define E.M.F?
The p.d of a supply when no current is being drawn
What is the Symbol and Units of Internal Resistance?
Symbol: r
Units: Ω
What is Internal Resistance?
The resistance of a power supply
What is Load?
AKA External Resistance
The resistance outside of a power supply
What is the equation of E.M.F?
E.M.F = Current (Internal resistance + external resistance)
ε = I x (R+r)
Or
E.M.F = p.d across load + (Current x Internal Resistance)
ε = V+Ir
What happens if a circuit has a small load?
A large curent will be drawn
The p.d lost on intenal resistance will be large
p.d supplied to load will be a lot less than the E.M.F
What is Kirchoff’s First Law?
The sum of the currents at a point is equal to Zero
Or
Total current in is equal to total current out
What is Kirchoff’s Second Law?
The sum of the E.M.F is equal to the sum of the p.d around a closed loop
Or
The total E.M.F provided is equal to the p.d across the components within a closed loop
What is a Rheostat?
A resistor where resistance is mechanically changed, by moving the point of contact allong it.
It is made of a long coil of wire
What is an LDR?
A resistor where resistance is based of light intensity.
Light Intensity↑ cause Tesistance↓
What is a potential divider circuit?
a simple circuit that uses resisters(or thermistors,rheostats or LDR’s) to supply a variable potential difference
What does a potential divider circuit look like?
Look in work book
