Restistance

• Learning objectives
• After this topic, you should know how to calculate resistance and how to investigate how length of wire affects resistance
• Resistance


  A measure of how difficult it is for a current to flow through a component
• Calculating resistance


  Use the equation: resistance = potential difference (voltage) (V) / current (A)
• Resistance


  Measured in ohms or Ω
• Steps to calculate resistance


  1. Step 1: Write down what you know

  2. Step 2: Write down the equation that links these values

  3. Step 3: Put the numbers into the equation and solve it
• Investigating the resistance in a wire

  1. Step 1: Build the circuit

  2. Step 2: Measure a distance of 10 cm

  3. Step 3: Increase the distance to 20 cm

  4. Step 4: Repeat until 70 cm

  5. Step 5: Calculate the resistance of each length

  6. Step 6: Plot a graph of resistance against length
• In the investigation it was important that the wire did not get hot
• The hotter the wire

  The greater the resistance
• Current


  A measure of the flow of electric charge
• Independent variable


  Length of wire
• Dependent variable


  Resistance
• Control variable


  Temperature of the wire
• The current through a wire is 0.5 A when the voltage across it is 4V
• Calculate the resistance of the wire

  Use the equation: resistance = voltage (V) / current (A)
• When the length of the wire is zero there is still a resistance of 0.2Ω
• Suggest a reason for this