2 - Electricity

• battery cell symbol?

  
• switch (open) symbol?

  
• switch (closed) symbol?

  
• lamp symbol?

  
• What is an electric current?

  - the flow of electric charge around a circuit
• What is the unit of electric current?

  - ampere (A)

  - shortened to amp
• How can we measure the current in a circuit?

  
  

  What is the symbol for this component?

  - by using an ammeter

  
• How will the current be affected if we put this component in another position?

  - current is never used up in a circuit

  - in series, the current is the same all the way around
• What direction does the electric current flow?

  - negative end of the cell to the positive end
• How do lamps light up in a circuit?

  - electrons carry energy from the cell to the lamp

  => electrons pass this energy to the components in the circuit, e.g. the lamp

  => electrical energy transferred to light and thermal energy
• What direction is the conventional current?

  - positive to negative end of the cell
• How can you know that a circuit is a series circuit?

  - no branches

  - current only flows in one path
• How do you know that a circuit is a parrelel circuit?

  - circuit conatins branches
• How is the current affected when the ammeter is placed in a different position in a parralel circuit?

  - current splits when passing through branches

  - different current in each branch
• What is key about the current in a parralel circuit?

  - the current in each branch adds up to the total current leaving the cell
• What does a potential difference of 1V tell us?

  - a potential difference of 1V tells us that 1J of energy is transferred for each coulomb of charge that is moving through the circuit
• How do we measure the potential diffeerrence in a circuit, what is the symbol for this component?


  - we can measure potential diffeence in a circuit using a voltmeter:

  
• Where does a voltmeter have to be placed in the circuit?


  - a voltmeter has to be placed in parralel to a circuit
• How does the potential difference in a circuit differ when we move the voltmeter's position, in a series circuit?


  - potential difference is the same everywhere in the circuit
• What does this constant potential difference show?

  - that all the electrical energy is transferred into other forms of energy when passing through components
• What happens to the brightness of one lamp if we add another lamp to the same circuit, in series?

  - lamp 1 becomes dimmer than how it was befoe the new lamp was added
• How is the potential difference divided by two lamps instead of one?

  - the total energy carried by the electric current has been shared between the two lamps
• What is the total potential difference across both lamps compared to the cell's?

  - the total p.d. across both lamps = the p.d.across the cell
• Why would a lamp with 6V be brighter than a lamp with 3V?

  - the 6V lamp is transferring more energy so itis brighter (6J per coulomb of charge)
• How does the potential difference differ when we move the position of the voltmeter, in a parrarel circuit?

  - for components connected in parallel, the potential difference across each component is the same
• What is a battery?

  
  

  What is the component symbol for a battery?

  - 2 or more cells connected together

  
• How must cells in a battery be connected?

  - they must both be facing the same direction
• What is electrical charge measured in?

  Coulombs, C
• What does a current of 1A tell us?

  - a current of 1A = 1C per second
• What is the equation for electrical charge?

  Q = I x t

  charge (C) = current (A) x time (s)

  
• What equation can we use to calculate the ENERGY TRANSFERRED by using the charge we have just worked out?

  E = Q x V

  energy (J) = charge (C) x p.d. (V)

  
• What is resistance?

  - when they move, electrons collide with atoms in the metal =>

  transferred electrical energy into other forms, e.g. thermal

  
  

  - resistance tells us the potential difference required to drive a current through a component
• What does a lower p.d. of one lamp tell us?

  - less p.d. needed to drive the current through the lamp

  => lower resistance
• What is the equation for resistance?

  V = IR ===> R = V/I

  resistant (ohms) = p.d. / current

  
• What is the symbol for the ohm?

  
• What is the component symbol for a resistor?

  
• How can a resistor be useful?

  - resistor increases resistance in circuit => reduce current

  => less p.d. across component

  => lamp is dimmer

  => LED does not get destroyed
• What is the relationship between the current through a resistor and the potential difference?

  
  

  What would happen to the potential difference if we increase the current?

  current ∝ potential difference

  
  

  => if we increase the current, the potential difference will also increase
• What is an ohmic conductor?

  
  

  - what must stay the same?

  A resistor in which the current is directly proportional to the potential difference at a constant temperature.
• What is a filament?

  -very tightly coiled wire