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# Conducting Well And Badly 2

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### Conducting Well And Badly 2

1. 1. Conducting Very Well - Conducting Very Badly A guide to electrical properties
2. 2. Good Conductor or Insulator? <ul><li>Does it allows electrical current to flow easily? </li></ul><ul><li>Electrons within a material allow current to flow </li></ul><ul><li>These electrons have become ‘free’ from the atoms in the materials - some materials ‘give-up’ their electrons more easily </li></ul>
3. 3. Good Conductor or Insulator? <ul><li>If it has a low Resistance, it lets more current through it - these are Conductors </li></ul><ul><li>If it has a high resistance, it lets less current through it - these are called Insulators </li></ul>
4. 4. How do we measure these characteristics? Resistance is measured in Ohms (Ω) Current is measured in Amperes (A) Voltage is measured in Voltage (V) Ohm’s Law V = I R
5. 5. CONDUCTIVITY  - Sm -1 RESISTIVITY  m
6. 6. Resistivity or Conductivity? <ul><li>Resistivity is the reciprocal of Conductivity </li></ul><ul><li>Both are dependent on the material </li></ul><ul><li>BUT: </li></ul><ul><li>What are Resistance and Conductance? </li></ul>
7. 7. Resistance <ul><li>Resistance is based on an individual object or component </li></ul><ul><li>The resistivity of silver is 10 -8 Ωm but what is the resistance of a piece of silver wire? </li></ul>
8. 8. Measuring the resistance of various wires <ul><li>Measure the resistance of various lengths of wire </li></ul><ul><li>What happens when: </li></ul><ul><ul><li>you double the length? </li></ul></ul><ul><ul><li>You double the cross-sectional area? </li></ul></ul>
9. 9. Resistance <ul><li>It depends on: </li></ul><ul><ul><li>The Cross-Sectional Area </li></ul></ul><ul><ul><li>The Length </li></ul></ul><ul><ul><li>and the resistivity (  ) of the material </li></ul></ul><ul><ul><li>Resistance =  L / A in Ohms </li></ul></ul>
10. 10. Conductance <ul><li>The reciprocal of Resistance </li></ul><ul><li>Resistance = 1 / Conductance </li></ul><ul><li>Therefore Conductance (G) = L /  A </li></ul><ul><li>or σ A / L (where σ is conductivity in Siemens m -1 ) </li></ul>
11. 11. Investigation <ul><li>Can we use these equations to calculate resistivity and conductivity? </li></ul><ul><li>We need to measure length, cross-sectional area and resistance. </li></ul><ul><li>We should be able to calculate the resistivity and/or conductivity of the material from the results </li></ul>