as electricity

• Electric current definition?


  Flow of charge per unit time (the rate of flow of charge)
• Electric current equation?


  I = Q/T
• Potential difference definition?


  Energy transferred per unit charge between two points on a circuit
• Potential difference equation?


  V = W/Q
• Resistance definition?


  Measure of how difficult it is for charge carriers to pass through a component
• Resistance equation?


  R = V/I
• What is Ohm's law?

  For an ohmic conductor, current is directly proportional to the potential difference (given physical conditions stay constant)
• Why must temperatures be kept constant when considering Ohm's law?


  Increase in physical conditions can increase the energy of atoms within a circuit, meaning charge carriers collide more often, leading to an increase in resistance.
• What does an IV graph of an ohmic conductor look like?


  Directly proportional through the origin
• What does the IV graph of a semi-conductor diode look like?


  Exponential when the threshold voltage is reached (smallest voltage needed for a current to flow) due to diodes having a forward bias
• What does the VI graph of a filament lamp look like?


  Not directly proportional for all voltage values, obeys Ohm's law until the resistance increases due to a change in physical factors
• How much resistance do ammeters have?

  Assumed to have zero, so they don't effect the measurement of current in a circuit
• How much resistance does a voltmeter have?


  Assumed infinity, so no current flows through them (voltmeters have to be connected in parallel) meaning the measurement of voltage isn't tampered
• What is resistivity?


  Measure of how easily a material conducts electricity
• What does the equation of resistivity tell you?

  The value of resistance through a material of length 1m and cross sectional area of 1m^2
• Why is a thermistor different to other components?

  Usually, the resistance increases with temperature in a metal conductor due to atoms gaining energy and colliding with the charge carriers, but thermistors act the opposite as the increase in temp leads to electrons being emitted from their atoms (increasing number of charge carriers in a circuit)
• What is an application of thermistors?

  Temperature sensor
• What is a superconductor?


  A material which at a critical temperature has zero resistivity
• What does the temperature of a superconductor depend on?

  The material it is made of
• What are applications of superconductors?


  Power cables - reduce energy loss during transmission

  Strong magnetic fields - stronger electric field = strong magnetic field
• What is the rule for adding resistance in series?

  \RT =$R1 +$$R2 +$$...$
• Resistivity equation?


  $\rho =$$\frac{RA}{L}$
• What is the rule for adding resistors in parallel?


  $\frac{1}{RT} =$$\frac{1}{R1} +$$\frac{1}{R2} +$$...$
• Power definition?


  Energy transferred over time (the rate of transfer of energy)
• What are the variations of the power equation?

  $P =$$VI =$$\frac{v^2}{R} =$$I^2R$
• How does the current act in a series circuit?


  The same everywhere in the circuit
• How does p.d act in a series circuit?


  Shared across all elements in the circuit (total sum of the voltages across all elements is equal to the terminal p.d)
• How does current act in a parallel circuit?


  The terminal current of the circuit is equal to the sum of the currents in each parallel set of branches
• How does p.d act in parallel circuits?


  The p.d is the same across every branch
• When battery cells are in parallel, how do you configure the voltage?


  $VT =$$V1 =$$V2 =$$...$, this is because current is split equally between branches, so the overall p.d is the same as if the current was flowing through a single cell
• When battery cells are in series, how do you configure the voltage?


  $VT =$$V1 +$$V2 +$$...$
• What quantities are always conserved in DC circuits?


  Charge and Energy
• How do we conserve the quantities in DC circuits?

  Kirchoff's First Law - Total current flowing into a junction is equal to the current flowing out that junction

  Kirchoff's Second Law - Sum of all voltages in a series circuit is equal to the terminal voltage
• Which of Kirchoff's law conserves charge?


  First, Q = IT, if current remains the same across each junction then Q remains the same
• Which of Kirchoff's Laws conserve energy?


  Second, if all voltages summed in series is equal to the voltage supplied, then energy is conserved
• What is a potential divider?


  A circuit with several resistors in series connected across a voltage source, used to produce a fraction of the source p.d
• How else can you make a potential divider?


  By using a variable resistor in place of one of the series resistors
• What is internal resistance?


  Resistance within a power source caused by electrons colliding with atoms inside the power source (some energy is lost before electrons leave the battery)
• What is the electromotive force?

  The energy transferred by a CELL per coulomb of charge that passes through it
• How can you calculate the total resistance in a circuit?

  $RT =$$R +$$r$