Electricity

• what is this?

  Diode

  
• what is this?

  LED

  
• what is this?

  Variable resistor

  
• what is this?

  thermistor

  
• what is this?

  LDR

  
• what is charge measured in?

  Coulombs C
• what is current?

  rate of flow of charge
• what is the purpose of resistance?

  slows down the flow of electrical charges in a circuit.
• units for resistance?

  The units of resistance are Ohms (Ω)
• what is the purpose of resistors?

  provide a given resistance to a circuit.
• The I-V graph for a resistor can be used to compare different resistors.
•  In an I-V graph, the current is on the y-axis and the potential difference is on the x-axis.
• in a I-V graph the gradient of the graph represents the resistance 
• which is an ohmic conductor?

  fixed resistor
• graph for fixed resistor?

  straight line through origin
• graph for filament lamp?

  S shape
• graph for diodes?

  IV curve
• Diodes allow current to flow one direction only and only when the potential difference has reached a threshold voltage.
• what is a LDR?

  Light-dependent resistor designed so that resistance decreases as light intensity increases
• what are non-ohmic resistors?

  when the current increases, the wire gets hot and the metal atoms in the wire vibrate, causing more resistance.
• why are rooms brighter in darker rooms?

  the resistance of the LDR is large. Therefore both the LDR and the bulb will have a high pd. This means the bulb gets more energy
• what happens to current in series circuit?

  Same
• what happens to pd in series?

  splits
• what happens to current in parallel?

  splits
• what happens to pd in parallel circuit?

  same
• what happens to resistance in series?

  total resistance increases as more components are added
• what happens to resistance in parallel circuits?

  resistance decreases as more components are added, because there are more paths for the current to pass through.
• UK's frequency?

  50 Hz
• UK's pd?

  230V
• what is direct current?

   the current is always flowing in the same direction
• what is alternating current?

  the current is constantly cycling between positive and negative directions.
• what current supply is UK?

  alternating
• what colour is the live wire and what is it?

  brown. provides alternating pd from power supply
• what colour is the neutral wire and what is it?

  blue. completes the circuit back to the ps. current flows through the neutral wire but the pd is 0V
• what colour is the earth wire and what is it?

  green and yellow- stops the cover of the electrical appliance from carrying current. only carries current when there is a fault
• If you touch the live wire, a large potential difference will be produced between your body and the wire= current will flow through you= electric shock
• even when the appliance is switched off there's still pd in live wire so can still get shocked
• If the live wire and Earth wire touch, this will create a low resistance path through= current can flow to the Earth
• Describe the energy transfers in a battery powered torch?

  1. Battery converts chemical energy into electrical energy
  2. Bulb converts electrical energy into light as well as waste energy in the form of heating
• What three things determine the power of a circuit device

  • The potential difference across the circuit
  • The current through the circuit
  • The amount of energy transferred in a given time