Current

• Van De graaf

  Electrons discharge through the air to the other sphere then to the ground

  the rubber belt causes friction between itself and the sphere

  sphere becomes negatively charged and the belt becomes positive
• Series circuits

  Current is the same everywhere in the circuit

  all the bulbs go off when the switch is opened

  if you add more bulb in series the current in the circuit is reduced and the bulbs are dimmer
• parallel circuit

  The current through the cell splits up when it comes to a junction

  each bulb can be controlled individually

  if you add more bulbs in parallel the bulbs all stay at the original brightness. The current stays the same through each bulb
• We use an ammeter connected in series to measure the current flowing through a circuit. The units for current are amperes (A)
• The voltage across a cell is a measure of the energy provided by the cell. We measure voltage using a voltmeter connected in parallel to a component; we say that a voltmeter is connected across a component. The units for voltage is volts (V)
• The voltage across a component is a measure of the energy transferred by that component.
• so basically, a simple resistor has a CONSTANT Resistance. When the current increases the voltage also increases and the resistance remains constant. 
• The size of the current flowing in a circuit depends on the voltage of the cell or power pack. And how easy it is for current to flow through the components in the circuit
• the resistance of a component is a way kf saying how easy or difficult it is for the current to flow theough It . The current in a circuit can be controlled by chabging the resistance of the components. Resistance can be added to a circuit using A component called a RESISTOR!!
• How to increase resistance

  Longer + Thin wires
• Insulating materials have high resistances
• Calculating resistance

  voltage = current x resistance
• A current voltage graph for a resistor is a straight line. This tells us that current is directly proportional to voltage
• Electrical Resistance

  How difficult it is for electrons to flow through something
• Practical method for determining resistance

  1. Voltmeter connected in parallel to the resistor

  2. Ammeter in series
• Electrical resistance

  • Measured in Ohms
  • Calculated using Ohm's Law
• R1 line is steeper

  R1 has greater resistance than R2
• Gradient of voltage/current graph

  Determines the resistance of a component
• Ohm's Law

  R= V÷I
• Voltage is the force that makes electrons flow.   Current is the rate of the flow of electrons.