P3

• What happens when insulating materials are rubbed together?

  They become (statically) electrically charged.
• Why can insulators become electrically charged when rubbed together?

  • Electrons are rubbed from one material onto the other.
  • The material gaining electrons becomes negatively charged.
  • The material losing electrons becomes equally positively charged.
• What is charging?

  The addition or removal of electrons from a material.
• How can charge be deflected?

  Using a gold leaf electroscope; the gold leaf is repelled by positive charge.
• What happens when two electrically charged objects are brought close together?

  They exert a force on each other.
• What happens when two oppositely charged objects are brought close together?


  They exert an attractive force on each other and attract.
• What happens when two identically charged objects are brought close together?

  They exert a repulsive force on each other and repel.
• Why are most bodies neutrally charged?

  They have an equal number of positive and negative charges.
• Give an example of a non-contact force.

  The repulsive or attractive force acting between two electrically charged objects.
• What is an electric field?

  A region in which a charged object will experience a non-contact electrical force.
• Where can electric fields be found?

  Surrounding any charged object.
• Describe the electric field around a charged particle.

  • Strongest closest to the object.
  • Decreases in strength as you move away from the object.
• What happens to the force between two charged objects when they are moved closer together?

  The force between them becomes stronger as the separation reduces.
• In situations where sparks are unwanted, what precaution must be taken to prevent the build up of static charge?

  Any surfaces that are rubbing against each other should be earthed to allow the materials to discharge.
• What is electric current?

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

  Current is the same at all points in a closed loop.
• Draw the circuit symbol for a switch.

  
• Draw the circuit symbol for a cell.

  
• Draw the circuit symbol for a battery.

  
• Draw the circuit symbol for a lamp.

  
• Draw the circuit symbol for a fuse.

  
• Draw the circuit for a voltmeter.

  
• Draw the circuit symbol for an ammeter.

  
• Draw the circuit symbol for a diode.

  
• Draw the circuit symbol for a resistor.

  
• Draw the circuit symbol for a thermistor.

  
• Draw the circuit symbol for a variable resistor.

  
• Draw the circuit symbol for an LDR.

  
• Draw the circuit symbol for an LED.

  
• What is a series circuit?

  A series circuit is one in which the same charge passes through all components, so the current through each component is the same.
• What is a parallel circuit?

  A circuit in which the charge is split between branches.
• What two factors does the current in a circuit depend on?

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

  • A conductor for which current and potential difference are directly proportional.
  • Resistance remains constant as current changes.
  • Temperature must be constant.
• List four components for which resistance is not constant as current changes.

  1. 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
  • Ions in metal have more energy, so vibrate more, causing more collisions with electrons as they flow through the metal, creating greater resistance.
• 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 a thermistor as temperature increases.

  The thermistor's resistance decreases.
• Give two examples of when a thermistor may be used.

  1. In a thermostat to turn a heater on below a certain temperature.
  2. In a freezer to turn on a cooler when the temperature becomes too high.
• State what happens to the resistance of a LDR as light intensity decreases.

  The LDR's resistance increases.
• Give an application for a LDR.

  • Street lamps or night lights.
  • When light levels become low enough, the light gains sufficient current to turn on.