Electric Resistance (DP IB Physics)

Electric Resistance

• As electrons move through a conductor within a circuit (or any other component), they collide with the metal ions and transfer some of their electrical potential energy to the positive ions of the metal

Free electrons collide with metal ions which resist their flow

• This transfer of energy results in an increase in the kinetic energy of the atoms in the lattice

  • This raises the overall internal energy of the metal

• The macroscopic result of this transfer is the heating up of the wire which causes resistance

• Some metals heat up more than others

  • The greater the heating effect, the higher the resistance

  • Copper has a low electrical resistance, making it an ideal material to make wires from

• All electrical components have resistance to different degrees, including the wires and batteries

• Voltmeters and ammeters are said to be ideal when

  • An ideal voltmeter has infinite resistance, such that no current passes through it

  • An ideal ammeter has zero resistance, such that all the current passes through it

Calculating Resistance

• The resistance R of a component is defined as:

  The ratio of the potential difference across the component to the current flowing through it 

• It is calculated as follows:

• Where:

  • V = potential difference (V)

  • I = electric current (A)

  • R = resistance (Ω)

• The units for resistance is ohms represented by the greek letter 'omega', Ω

• The higher the resistance of a component, the lower the current flowing through it and vice versa

• In terms of SI base units: 1 Ω = 1 kg m² s^–3 A^–2