Electricity Flashcards
How does current flow
Positive ——-> Negative
How do electrons flow in wires
Opposite direction to current
Definition of potential difference
Work done per unit charge
What is an ohmic conductor and state an assumption about it
A component with constant resistance
Temperature remains constant
Equations for resistance in series and parallel
Series - R1 + R2 + ….. = Rtotal
Parallel - (1/R1 + 1/R2 + ……)^-1
What are both kirchoffs law
KCL - For any point in a circuit current in = current out
KVL - For any loop in a circuit the sum of directed voltages = 0
What direction does voltage act in
Opposite to current
I/V graphs explain the main 4
Metallic conductor - Straight line (steeper-low resistance shallower - high resistance)
Filament lamp - small to steep to small gradient (Resistance of metal increases as temperature increases)
Thermistor - Shallower filament lamp
Diode - Zero then sudden increase (around 0.7V)
Explain a practical for resistivity
Power supply attached to a flying lead with a voltmeter and ammeter
Find wire cross sectional area using a micrometer, find an average diameter
Attach lead to wire measuring length of wire, voltmeter and ammeter reading
Find resistance using V=IR, repeat to find an average
Repeat for different lengths and plot a graph of R against L
Gradient of line of best fit x cross sectional area = resistivity
If temperature is not kept constant, random errors could occur
What is a superconductor
A material with zero resistance/resistivity
A material below the critical temperature
Definition of emf
Total work done per unit charge by the battery
How do you add emf in parallel
emf total = E1 = E2
How do you add emf in series
emf total = E1 + E2
What does IR represent in an emf equation
The terminal pd across the cell
What does Ir represent in an emf equation
The lost pd across internal resistance
