Charge and current

Charge and current

1. Definitions

   • An electric current is the rate of flow of charge. Charge = current * time
     • Charge is carried by electrons in a circuit.
       • metals are good conductors as they have free electrons which are able to move. "a sea of free electrons"
     • will only flow if there's a voltage.
   • Voltage( or potential difference) is the driving force that pushes the current around a circuit
     • unit = volt, V
   • resistance is something in a circuit that slows the flow of charge down.
     • measured in ohm.
   • The ammeter
     • measures the current flowing through the component.
     • must be placed in series so it's connected to the line with the component.
       • Voltage- current graphs.
         • fixed resistor
           • filament graph
             • as the temperature increases, the resistance increases.
             • diode
               • current will only flow in one direction.
   • The voltmeter
     • measures the voltage.
     • must be placed in parallel around the component. not around the cell or variable resistor.
       • voltage = current * resistance.

2. D.C. = direct current.

   • This is provided by cells and bateries.
   • it is a current that flows in one direction
   • Same voltage, same direction = straight line on oscilloscope.

3. A>C> = Alternating current

   • from mains electricity.

4. Energy is supplied to the charge at a power source ( such as a cell or battery) .

   • The charge transfers this energy if the voltage drops anywhere throughout the circuit.
     • The bigger the change in voltage, the more energy is transferred for a given amount of charge.
       • A battery therefore with a bigger voltage will supply more energy to the circuit for every coulomb of charge because the charge at the start is higher.
   • 1 volt = 1 joule or 1 coulomb

5. Current is conserved at a junction.

6. Light dependent resistors.

Images and files in the map