Electric Current Remember: Copper atoms are much bigger than electrons and are packed together in the wire October 2015

In an electric c____, current is 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______. Current lamps ircuit lectrons ore ires erminal

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) 10 October 2015 Ω Omega How many different words can you spell from the word resistance?

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

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

Current in parallel A1A1 A2A2 A3A3 A4A4 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? A 1 = 0.6A A 2 = _____? A 3 = 0.2A A 4 = _____? 10 October 2015

Current in parallel A1A1 A2A2 A3A3 A4A4 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? A 1 = 0.6A A 2 = 0.4A (A 1 -A 3 = 0.6A-0.2A) A 3 = 0.2A A 4 = 0.6A (A 1 = A 4 )

Measuring Voltage V2V2 V3V3 V1V1 NB Voltmeters are connected in parallel VoltmeterVoltage (V) V1V1 1.5 V2V2 0.6 V3V3 0.9 Voltage measures how energy changes around the circuit. It compares the energy in one part with another and shows the difference. In series V 1 = V 2 +V 3

Voltage in Parallel V1V1 V2V2 V3V3 Voltage only changes when energy changes. In this circuit energy changes happen at the cell and the bulbs. V 1 = V 2 = V 3 VoltmeterVoltage (V) V1V1 1.5 V2V2 V3V3

Measuring Resistance V A Resistance = Voltage Current 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. Voltage (V) Current (A) Resistance (Ω)

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

ISA Answers 1.I was trying to find out if the current flowing through a resistor depends on the voltage across it. 2.Independent variable = Voltage Dependent variable = Current 3.Voltmeter or Ammeter 4.The smallest scale division was 0.01V or 0.01A 5.Smaller scale division means more precise measurements 6.Use the same resistor Different resistance values change the current 8.As the Voltage increases the current increases

Section 2 10.As temperature increases the resistance falls 11.Range 0º C to 150ºC No. 150ºC too high for room temperatures. 12.At these temperatures resistance only changes very slightly ºC circled. Not anomalous. More likely to be 25ºC 14.Thermistor tested might not be typical between 50 and 200 (5 to 20%) 15.Results would be more reliable 16.Have smaller intervals between readings

17.Company was changing the results. Avoiding bad publicity. Would damage the companies reputation. 18.Improves the reliability 19.They have had a scale marked on them A range either side of the expected value that is considered acceptable 5%

Testing the effect of current on a wire A Test Wire Voltage (V) Current (A) Resistance (Ohms) CircuitResults

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) 10 October 2015 Ω Omega How many different words can you spell from the word resistance?

Resistance of a wire (ISA) To investigate which factors change the resistance of a wire.10 October 2015 Apparatus: Resistance wire, Voltmeter, Ammeter, Power supply, Leads, Crocodile clips, metre ruler, Variable resistor. V A Test Wire