Physics Topic 3

• Can electric force be attractive or repulsive?

  Both and can act at a distance
• What can electric force act as?

  bodies that have net charge
• what are the two types of charge?

  positive and negative
• what do many charged particles form when moved together?

  an electric current
• how is the neutral charge in an atom balanced?

  the negative charge of electrons is balanced by the positive charge of the nucleus
• what is the unit of charge?

  Coulombs, C
• What happens when there is an imbalance of positive and negative charge?

  forces between objects much larger than atoms can be observed
• why are the observations or phenomena called static electricity or electrostatics?

  because the charged particles are not flowing
• what happens to an object when electrons are transferred from one object to another?

  one object will have an excess of electrons and negative charge, the other object will have a shortage of electrons and a positive charge
• what happens when an object is charged by friction?

  they exert electrical force- attraction or repulsion- on other charged objects
• what can there be in spaces between objects with different levels of charge?

  strong forces on the charged particles inside atoms
• what are metals?

  conductors of electricity
• what happens when many electrons move in the same direction in a wire?

  there is an electric current
• what is current measured in?

  amps (A)
• what is current equal to?

  the rate of flow of charge
• why can a conductor not keep excess electric charge?

  electrons flow in or out of it too easily
• How can electric current inside a closed loop of wire be continuous?

  if the electron experience a continuous force from a source of energy
• what part of a circuit can create a continuous force?

  batteries and cells
• what are ammeters used to measure?

  current
• how are ammeters connected into ciruits?

  so that current can pass through them
• What is there when current flows through an electrical conductor such as a metal wire?

  resistance
• what does the resistance in the wire mean?

  a wire can be heated by an electrical current, energy passes from the wire to the surroundings
• What can an increase in p.d increase?

  current
• what can an increase in resistance decrease?

  the current
• what is current proportional to?

  voltage
• what doesnt change if the temperature of a metal wire doesnt change?

  resistance
• describe a current-voltage graph

  a straight like that passes through the origin of the graph
• what is the relationship between current and voltage?

  linear
• what happens to the resistance in a wire that gets hotter as voltage and current gets bigger?

  resistance increases
• How does a thermistor behave?

  If the temperature increases, the resistance falls.
• What happens to resistance as it becomes hotter?

  more electrons become free to move so resistance comes down
• for a thermistor what is the current-voltage relationship?

  non linear
• what are thermistors sensitive to?

  changes in temp
• what can thermistors be used as?

  electrical temperature sensors
• what are the current-voltage relationships for diodes and ldrs?

  non linear
• what do diodes allow?

  current flow in one direction
• what happens for ldrs when light intensity increases?

  resistance goes down
• what happens when voltage is in the reverse direction?

  no current flows
• what is resistance measured in?

  Ohms (Ω)
• What are voltmeters?

  devices used to measure pd or voltage