Electricity

• What is the direction of conventional current flow?

  From positive terminal to negative terminal
• What is the actual flow of electrons?

  From negative terminal to positive terminal
• What is the value of the elementary charge, e?

  1.60 x 10^-19 C
• What does it mean that net charge is quantised?

  It is a multiple of the elementary charge
• What is electric current (I)?

  The flow of charge per unit time
• How is current (I) calculated?

  I = ΔQ / Δt
• What is potential difference (V)?

  Energy transferred per unit charge
• How is potential difference (V) calculated?

  V = W / Q
• What is resistance (R)?

  Measure of difficulty for charge carriers
• How is resistance (R) calculated?

  R = V / I
• What does Ohm's law state for an ohmic conductor?

  Current is directly proportional to potential difference
• What does the current-voltage graph of an ohmic conductor look like?

  A straight line through the origin

  
• What is the forward bias of a semiconductor diode?

  Direction allowing current to flow easily
• What happens in reverse bias for a semiconductor diode?

  Resistance is extremely high, low current flows
• How does a filament lamp behave as current increases?

  Resistance increases as current increases
• When does a filament lamp obey Ohm's law?

  At low currents when wire doesn't heat significantly
• What is assumed about ammeters in circuits?

  They have zero resistance
• What is assumed about voltmeters in circuits?

  They have infinite resistance
• What is resistivity (ρ)?

  Measure of how easily a material conducts electricity
• How is resistivity (ρ) calculated?

  ρ = R * A / L
• What happens to resistance when the temperature of a metal conductor increases?

  Resistance increases due to more collisions
• How does a thermistor behave as temperature increases?

  Resistance decreases as temperature increases
• What is a common application of a thermistor?

  Temperature sensor in circuits
• What is a superconductor?

  Material with zero resistivity below critical temperature

  
• What is the critical temperature of a superconductor?

  Temperature below which it has zero resistivity

  
• What are applications of superconductors?

  Power cables and strong magnetic fields
• What is the rule for resistors in series?

  RT = R1 + R2 + R3 + ...
• What is the rule for resistors in parallel?

  1/RT = 1/R1 + 1/R2 + 1/R3 + ...
• How do you find total resistance in a mixed circuit?

  Use series and parallel rules together
• What is power (P) in electrical terms?

  Energy transferred over time
• How is power (P) calculated?

  P = E / t
• What is another formula for power involving current and voltage?

  P = V * I
• How can power be expressed in terms of resistance?

  P = V^2 / R
• How is energy transferred calculated from power?

  E = P * t
• How do you find energy transferred by a lamp with 60 W power in 2 minutes?

  E = 60 W * 120 s = 7200 J
• How do you find current in a lamp connected to 240 V with 60 W power?

  I = P / V = 0.25 A
• What is true about current in a series circuit?

  Current is the same everywhere in the circuit
• What is true about potential difference in a series circuit?

  Total voltage equals the sum across all elements
• What is true about current in a parallel circuit?

  Sum of currents in branches equals total current
• What is true about potential difference in a parallel circuit?

  Potential difference across each branch is the same