Physics paper 1 electricty

• What is an electric current

  Flow of electrons through a circuit

  Flows thru the negative end of a cell to the positive

  Electrons carry the energy from the cell

  Pass this energy through to the components
• What is the component used for measuring current in a circuit

  Ammeter
• What is conventional current

  The way the current is drawn in the opposite way
• describe current in a parallel circuit

  current in branches adds up to the total current leaving the cell
• What is potential difference telling us

  Pd of 1 volt tells us that 1 joule of energy is transferred for each coulomb of charge that is moving through the circuit
• What component uses pd to be measured

  Voltmeter
• What does it mean if a bulb has a higher potential difference

  It will be brighter as it’s transferring more energy
• Potential difference in parallel circuits

  Potential Difference across each component is the same
• What is electrical charge measured in

  Coulombs
• What does a current of 1 ampere mean

  1 coulomb of charge flowing per second
• What is the size of electrical current

  Rate of flow of electrical Charge
• Formula for charge flow

  $Q\ =$$I\ t$
• What’s the formula for energy transfer in components

  $E=$$Q\ V$
• What is meant by resistance

  as electrons move through a conductor

  collide with atoms in a metal

  electrical energy is then transferred into other forms
• What does the higher voltage mean

  higher resistance
• Formula for resistance 


  $R=$$\frac{V}{I}$
• What does the resistance then tell you

  The potential difference required to drive a current through a component
• what is an ohmic conductor And it’s conditions

  Current and pd are directly proportional

  Resistance remains constant as current changes

  Temp must be constant
• List 4 components in which resistance is not constant as current changes

  Lamps

  Diodes

  Thermistors

  Ldr
• What happens to the resistance of the filament lamp as temp increases

  Resistance increases

  Ions in the metal have more energy

  so more vibrations

  causing more collision with electrons

  as flow through the metal creating greater resistance to current flow
• what is diff ab current flow in a Diode

  Current only flows in one direction

  Resistance is very high in the other direction preventing current flow
• Why are diodes useful

  Controlling the flow of the current
• Why are leds useful

  Extremely energy efficient source of light
• What happens to resistance of thermistor as temp increases

  Thermistors resistance decreases
• how do you calculate resistance in series

  They add together

  as current has to pass through each resistor in turn it cannot bypass any resistor
• What is the total resistance of 2 resistors in a parallel 


  Less than the resistance of the smallest individual resistor
• Explain why the total resistance is less than the smallest Resistor

  We have two pathways for the current to take

  More total current will flow through the circuit
• What happens when the current increases but the pd doesn’t change

  Total resistance decreases