Current, Potential Difference and Resistance

• Label all these circuit symbols:

  A) Open Switch

  B) Closed Switch

  C) Lamp

  D) Voltmeter

  E) Ammeter

  F) Resistor

  G) LDR

  H) Thermistor

  I) Variable Resistor

  J) Diode

  K) LED

  L) Fuse

  M) Cell

  N) Battery

  
• What is electric current?

  The flow of charge
• What can be said about the value of current at any point in a single point in a single closed loop?

  Current is the same at all points in a closed loop.
• What two factors does current depend on?

  Potential Difference (V), Resistance (R)
• What is an 'Ohmic Conductor'? State the condition required.

  A conductor for which current and potential difference are always directly proporitional

  Resistance remains constant as current changes

  Temperature must be constant.
• What happens to the resistance of the filament lamp as resistance increases?

  Resistance increases

  Ions in a metal have more energy, so vibrate more, causing more collisons with electrons as they flow through the metal, creating greater resistance to current flow.
• What is different about current flow through a diode?

  The current only flows in one direction

  Resistance is very high in the other direction, preventing current flow
• State what happens to the resistance of the thermistor as the temperature increases.

  Decreases
• Give two ways in which a thermistor can be used.

  1: In a thermostat to turn on a heater when temperature goes below a certain temperature

  2: In a freezer to turn on a cooler when temperature becomes too high.
• State what happens to the resistance of an LDR as light intenstity DECREASES.

  Increases.
• Give an application of LDR:

  Street lights often use LDRs

  When light levels go too low, the current gains sufficent current to turn on