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Electric Current

Electric Current. 30 November 2014. +. Remember: Copper atoms are much bigger than electrons and are packed together in the wire. Current.

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Electric Current

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  1. Electric Current 30 November 2014 + Remember: Copper atoms are much bigger than electrons and are packed together in the wire.

  2. Current In an electric c____, currentis the flow of e_______. The bigger the current, the m___ electrons are flowing around the circuit. The w___ carry the electrons from one terminal around the circuit to the other t______. ircuit ore lectrons ires erminal lamps

  3. Ω Omega 30 November 2014 5.2 Resistance • Resistance is measured using an ammeter and a voltmeter. • Resistance = Voltage  Current • This is called Ohm’s Law • Resistance is measured in Ohm’s (Ω) How many different words can you spell from the word resistance?

  4. A A A Measuring Current Current is measured using an ammeter connected in series. What will the 3 ammeters read in this circuit? 1 3 2 Ammeter 1 = 0.15A, Ammeter 2 = ____, Ammeter 3 = ____

  5. A A A Measuring Current Current is measured using an ammeter connected in series. What will the 3 ammeters read in this circuit? 1 3 2 Ammeter 1 = 0.15A, Ammeter 2 = 0.15A, Ammeter 3 = 0.15A In a series circuit the current is always the same.

  6. 30 November 2014 A1 A4 A2 A3 Current in parallel In a parallel circuit the current can split depending on how difficult each route is. The total current into and out of the supply is always the same. What are the missing currents? A1 = 0.6A A2 = _____? A3 = 0.2A A4 = _____?

  7. A1 A4 A2 A3 Current in parallel In a parallel circuit the current can split depending on how difficult each route is. The total current into and out of the supply is always the same. What are the missing currents? A1 = 0.6A A2 = 0.4A (A1-A3 = 0.6A-0.2A) A3 = 0.2A A4 = 0.6A (A1 = A4)

  8. V1 NB Voltmeters are connected in parallel V2 V3 Measuring Voltage Voltage measures how energy changes around the circuit. It compares the energy in one part with another and shows the difference. In series V1 = V2 +V3

  9. V1 V2 V3 Voltage in Parallel Voltage only changes when energy changes. In this circuit energy changes happen at the cell and the bulbs. V1 = V2 = V3

  10. Resistance = Voltage Current A V Measuring Resistance Set up the circuit as shown below: Slowly move the variable resistor and for each setting record the current in amps and the voltage in volts. Plot a graph of your results.

  11. Correct type of graph Bar chart for categoric data Line graph for continuous data Graphs Points plotted correctly Suitable labels – Quantity (Units) Scale uniform

  12. ISA Answers • I was trying to find out if the current flowing through a resistor depends on the voltage across it. • Independent variable = Voltage • Dependent variable = Current • Voltmeter or Ammeter • The smallest scale division was 0.01V or 0.01A • Smaller scale division means more precise measurements • Use the same resistor • Different resistance values change the current • As the Voltage increases the current increases

  13. Section 2 • As temperature increases the resistance falls • Range 0º C to 150ºC • No. 150ºC too high for room temperatures. • At these temperatures resistance only changes very slightly. • 50ºC circled. • Not anomalous. More likely to be 25ºC • Thermistor tested might not be typical • between 50 and 200 (5 to 20%) • Results would be more reliable • Have smaller intervals between readings

  14. Company was changing the results. Avoiding bad publicity. Would damage the companies reputation. • Improves the reliability • They have had a scale marked on them A range either side of the expected value that is considered acceptable 5%

  15. Test Wire A Testing the effect of current on a wire Circuit Results

  16. Ω Omega 30 November 2014 5.2 Resistance • Resistance is measured using an ammeter and a voltmeter. • Resistance = Voltage  Current • This is called Ohm’s Law • Resistance is measured in Ohm’s (Ω) How many different words can you spell from the word resistance?

  17. 30 November 2014 Resistance of a wire (ISA) • To investigate which factors change the resistance of a wire. Apparatus: Resistance wire, Voltmeter, Ammeter, Power supply, Leads, Crocodile clips, metre ruler, Variable resistor. Test Wire A V

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