(PP8) resistance of a metal conductor

• the resistance of a metallic conductor at constant temperature depends on length
• Independent Variable is the length of wire.
• Dependent Variable is the resistance of the wire. 
• Control Variables are the material, the cross section area and the temperature of the wire. These are kept the same by not changing the wire during the experiment, by keeping the current small and opening the switching between readings.
• Resistance R = Voltage V / current I
• Prediction - as the length of wire increases, the resistance will increase.
• The greater the length of wire the greater the number of collisions between the free electrons and metal ions.

  This will result in greater resistance.
• The temperature of the wire must be kept constant.

  When a current flows through a conductor there is a heating effect.

  Electrical energy is converted to heat energy.

  To ensure the temperature does not increase, switch off between readings and keep the current as low as possible.
• Read the ammeter and voltmeter accurately by reading the scale from directly above the pointer or use digital instruments.
• for a metal wire at constant temperature, the resistance is directly proportional to the length of the wire.

  If you double the length of the wire you double its resistance.
• the resistance of a metallic conductor at constant temperature depends on the area of cross section.
• A thicker wire has a smaller resistance than a thin wire.
• resistance and cross section area are inversely proportional.

  If you double the cross section area you half the resistance of the wire
• the resistance of a metallic conductor at constant temperature depends on the material of the conductor
• wires of different material have different resistance