Resistivity Resistivity Introduction KWLD • What do you know about resistance in materials? • What do you want to know about resistance in materials? Resistivity Check it Out Check out the multimeter Materials • Multimeter. • 1 - 470 resistor • 1 – 1.0K resistor • 1 – 1.5K resistor • 1 – 1.0M resistor • Breadboard • Breadboard wire pack 6V battery pack Resistivity Check it Out 1. Plug the red (positive) lead into the V (Voltage/Resistance) connection hole. Multimeter – Resistor Measurements 2. Plug the black (negative) lead into the COM (Common) Readout Volts DC Volts AC connection hole. Measurement Range Dial Amps Ohms 3. Turn the measurement range Resistance Current 10A Resistance mA COM V dial into the resistance Settings () settings area. Positive Lead Negative Lead 4. Set the range setting to a level Resistor higher than the resistance of the resistor you will be measuring. Resistivity Check it Out 5. Touch the red lead to one end of the resistor and the black lead to the other end. 6. The readout will display the resistance value according to the scale you set. Resistivity Check it Out 7. Record your actual measured resistance value for the resistor and the corresponding “color bands” on the resistor in the table in your Lab Journal. 8. Set these resistors aside, they will be used later. 9. Turn the measurement dial back to OFF when not in use to conserve the battery. Resistor Actual measurement Color bands 470 1.0K 1.5K 1.0M Resistivity Team Challenge • Ohm’s law: V=I*R • Use Ohm’s law to fill in the empty table cells in your Lab Journal. Resistivity Team Challenge • Ohm’s Law Answers Formula Voltage Current Resistance V=I*R 3.6 3.6mA 1.0K I=V/R 9.0V 9.0A 1.0K R=V/I 9.0V 3.6mA 2.5K I=V/R 6.0V 3.0A 470 Resistivity Team Challenge Goal: experience the relationship is between voltage, current, and resistance in an electronic circuit. Materials List • Calculator • Multimeter and leads • 1 – 470W resistor • 1 – 1.0KW resistor • 1 – 1.5KW resistor • 1 – 1.0MW resistor • Breadboard • Breadboard wire pack (pre-trimmed wires for making connections on the breadboard) • 6V battery pack (includes 4 – “AA” batteries) Resistivity Team Challenge Bread Board Layout The holes in these columns are connected up & down The holes in these rows are connected across Resistivity Team Challenge 1. Connect battery to the ends of the “+” and “-“ rows with the red wire going to the “+” and the black wire going to the “-“. 2. Place the 470 resistor with one end in a hole in one column and the other end in a hole in another column. 3. Connect a small wire from a hole in the “+” row into a hole corresponding to the column where one end of the resistor is connected. 4. Connect a small wire from a hole in the “-” row into a hole corresponding to the column where the other end of the resistor is connected. Resistivity Team Challenge 5. The breadboard layout should Resistor Circuit Layout resemble the image at right. • To measure the voltage across the resistor use the following setup and verify that the batteries are producing approximately - 6.0V. Be sure to set the + multimeter on the 20 setting in Battery Red the DC Voltage setup area so Battery Black Battery that it will be able to measure Battery 6.0V without over-ranging. • Record the voltage measurement. Resistivity Team Challenge Measure the current in the circuit 6. Insert the meter between the “+” row and the upper side of the resistor (remove the little wire that was connecting this side of the resistor to the “+” row). Resistivity Team Challenge 7. Verify that your current calculation was accurate. 8. Be sure to set the multimeter on the 20m setting in the DC current setup area 9. Be sure that your red lead is connected to the “mA” connection of the meter instead of the “V” connection. 10. Record your current measurement. Resistivity Observations and Analysis • Were there slight differences in your measured values from your calculated values? • Why or why not? • Why did the buzzer get softer with increased resistance? • What is required to increase the buzzer sound? Resistivity Observations and Analysis Can you see the relationship between resistance, voltage, and current? (V=IR) • For constant resistance, the relationship between voltage and current look like the plot in (a). (a) • For constant current, the relationship between voltage and resistance also looks like (a). • For constant voltage, the relationship between current and resistance looks like (b). (b) Resistivity Conclusions Finish the KWLD • What did you learn about resistance in materials? • What can you do with what you learned about resistance in materials? Resistivity Make the Connection 1. Use your multimeter to measure the resistance of your body from one hand to the other. 2. Set the meter to 20M. 3. Grab the tip of the red lead between two fingers in your right hand. 4. Grab the tip of the black lead between two fingers in your left hand. 5. Squeeze tightly, and note the resistance measurement on the readout. 6. Record your measurement. What factors do you think cause the variations between the measurements of various people? Resistivity Make the Connection 5. Now lick the four fingers you used to get them wet and repeat the measurement. 6. Record the new measurement. Does your body conduct electricity? How did licking your fingers affect the measurement? Compare your measurements with others. How do the measurements vary? What factors do you think cause the variations between the measurements of various people? Resistivity Make the Connection • What affects the resistivity of various materials? • How might doping can change the resistance of materials?