Electricity

• What is meant by D.C?


  Direct current - Current flows continously around the circuit in the same direction
• Why is a variable resistor usually used than a fixed resistor?


  Varying the circuit resistance allows the current to be varied
• The total energy carried by the current in a series circuit is shared..


  Between the components
• Why would a lamp of 6V be brighter than a lamp of 3V?


  As it is transferring more energy
• Why do series circuits only have current flowing in one path?

  As they have no branches
• How is electric current measured?


  Using an ammeter
• Why is the current the same all the way around a series circuit?


  As current is never used up.
• What energy store does a cell have, and what is it transferred to.


  Has a chemical energy store which is transferred to electric energy which is carried by electrons.
• 1 Joule is equal to..


  1 volt
• How is potential difference measured?


  Using a voltmeter
• What happens if two lamps are added in a series circuit?


  Both lamps would be dimmer than a single lamp
• What happens in a series circuit when a switch is closed?


  Current flows from the negative end of the cell, to the positive end of the cell
• What do electrons carry from the cell?


  Energy
• Where do electrons carry the energy to?


  The components of the circuit
• What happens when electrons return to the cell?


  They are carrying less energy than they were at the negative end of the cell
• What does it mean when a parallel circuit has an open switch/branches?

  Some of current passes through both branches
• In a parallel circuit, what does the current in the branches add up to?


  The total amount of current leaving the cellae
• Diodes..

  Only allow current to flow one way around a circuit
• For wires and resistors, increasing the temperature will increase the..

  Resistance
• In a series circuit, the current is..

  The same everywhere in the circuit
• In a series circuit, the potential difference of the battery is..

  Shared across all of the components
• What happens to the resistance of a thermistor if the temperature decreases?

  High resistance (Increases)
• What happens to the resistance of a thermistor if the temperature increases?

  Low resistance (decreases)
• What happens to the resistance of an LDR if there are low light levels?

  LDR has a high resistance
• What happens to the resistance of an LDR if the light intensity increases?

  Decreases
• How does current flow when using a a semiconductor diode?

  Flows in one direction only.
• What are diodes used for?

  To convert an alternating current into a direct current
• Where should an ammeter be placed in a circuit if you are measuring the current through a component?

  In series
• Where should a voltmeter be placed in a circuit if you are measuring the voltage through a component?

  In parallel
• Describe a method to investigate how changing the length of the wire affects resistance

  1. Connect the crocodile clips to the resistance wire, 100 centimetres (cm) apart.
  2. Record the reading on the ammeter and on the voltmeter.
  3. Move one of the crocodile clips closer until they are 90 cm apart.
  4. Record the new readings on the ammeter and the voltmeter.
  5. Repeat the previous steps reducing the length of the wire by 10 cm each time down to a minimum length of 10 cm.
  6. Use the results to calculate the resistance of each length of wire by using R = V/I, where R is resistance, V is voltage and I is current.
  7. Plot a graph of resistance against length for the resistance wire.
• Describe a method to investigate the relationship between current and potential difference for a bulb, resistor and a diode

  1. Ensure that the power supply is set to zero at the start.
  2. Record the reading on the voltmeter and ammeter.
  3. Use the variable resistor to alter the potential difference.
  4. Record the new readings on the voltmeter and ammeter.
  5. Repeat steps three to four, each time increasing the potential difference slightly.
  6. Reverse the power supply connections and repeat steps two to six.
  7. Plot a graph of current against potential difference for each component.
  8. Repeat the experiment but replace the fixed resistor with a bulb.
• What happens if the potential difference of the bulb increases?

  The temperature of the thin wire inside the bulb increases. A higher temperature increases the vibrations of the ions in the filament, making it harder for the electrons to get past
• What happens as electrons flow through wires?

  They collide with the ions in the wire, causing the ions to vibrate more. The increased vibration of the ions increases the temperature of the wire. Energy has been transferred from the chemical energy store of the battery into the internal energy store of the wire.
• How would direct current appear on a voltage-time graph?

  As a horizontal line
• How would an alternating current appear on a voltage-time graph?

  A curve alternating between positive and negative voltages (Positive and negative values indicate the direction of current flow)
• What happens to the thin wire in a fuse if the current gets too high?

  Melts
• What could happen if there was no earth wire and the live wire becomes loose?

  There is a danger that it will touch the case. The next person who uses the appliance could get electrocuted.
• What does the earth wire do in case there is a fault?

  Provides a low resistance path to the ground. In case of a fault, the live current passing through the case will follow this path to the ground instead of passing through a person.
• What happens once the fuse has melted?

  The circuit is broken and no more current flows through the device. The device is no longer live and therefore there is no more risk of electrocution.
• What happens to current if voltage increases?

  Decreases