resistance

    Cards (14)

    • how does resistance affect current in a circuit?
      • as total resistance of circuit increases
      • current flowing through circuit decreases
    • how can the current in a circuit be varied?
      • use a variable resistor
    • give the equation linking current and resistance
      V = IR
    • how is total resistance affected by two resistors in series?
      • total resistance increases
      • equal to the sum of the two resistors
    • how is total resistance affected by two resistors in parallel?
      • total resistance decreases
      • less than resistance of the resistor with the lowest resistance
    • what is an Ohmic conductor, state the condition required
      • conductor for current + potential difference = directly proportional
      • resistance remains constant as current changes
      • temperature must be constant
    • list 4 components in which resistance is not constant as current changes
      1. filament lamps
      2. diodes
      3. thermistors
      4. light dependent resistors (LDRs)
    • what happens to the resistance of a filament lamp as the temperature increases? Why?
      • resistance increases
      • metal ions = more kinetic energy: vibrate more, colliding more frequently with electrons as they flow through metal
      • creates more resistance to current flow
    • what is different about current flow through a diode?
      • current only flows in one direction
      • resistance = very high in other direction, preventing current flow
    • state what happens to the resistance of a thermistor as temperature increases
      thermistor's resistance decreases
    • give examples of when a thermistor may be used
      • in a thermostat: turn a heater on below a certain temperature
      • in a freezer: turn on a cooler when temperature = too high
    • state what happens to the resistance of an LDR as light intensity decreases
      LDR's resistance increases
    • give applications for an LDR
      • street lamps or night lights
      • when light levels drop (night), resistance and the light gains sufficient current to turn on
    • how do diodes work?
      • only allows current to flow in one direction
      • if current is flowing the right way, resistance is large for small voltages (up to 0.6 V)
      • but then at higher voltage becomes very small