Resistivity

1
Resistivity
2
Introduction

• KWLD
• What do you know about resistance in materials?
• What do you want to know about resistance in
  materials?

3
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

4
Check it Out

1. Plug the red (positive) lead into the V?
   (Voltage/Resistance) connection hole.
2. Plug the black (negative) lead into the COM
   (Common) connection hole.
3. Turn the measurement range dial into the
   resistance settings area.
4. Set the range setting to a level higher than the
   resistance of the resistor you will be measuring.

5
Check it Out

• Touch the red lead to one end of the resistor and
  the black lead to the other end.
• The readout will display the resistance value
  according to the scale you set.

6
Check it Out

• Record your actual measured resistance value for
  the resistor and the corresponding color bands
  on the resistor in the table in your Lab Journal.
• Set these resistors aside, they will be used
  later.
• 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?
7
Team Challenge

• Ohms law VIR
• Use Ohms law to fill in the empty table cells in
  your Lab Journal.

8
Team Challenge

• Ohms Law Answers

Formula Voltage Current Resistance
VIR 3.6 3.6mA 1.0K?
IV/R 9.0V 9.0A 1.0K?
RV/I 9.0V 3.6mA 2.5K?
IV/R 6.0V 3.0A 470?
9
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)

10
Team Challenge
11
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.

12
Team Challenge

• The breadboard layout should 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 the DC
  Voltage setup area so that it will be able to
  measure 6.0V without over-ranging.
• Record the voltage measurement.

13
Team Challenge

• Measure the current in the circuit
• 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).

14
Team Challenge

1. Verify that your current calculation was
   accurate.
2. Be sure to set the multimeter on the 20m setting
   in the DC current setup area
3. Be sure that your red lead is connected to the
   mA connection of the meter instead of the V?
   connection.
4. Record your current measurement.

15
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?

16
Observations and Analysis

• Can you see the relationship between resistance,
  voltage, and current? (VIR)
• For constant resistance, the relationship between
  voltage and current look like the plot in (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).

17
Conclusions

• Finish the KWLD
• What did you learn about resistance in materials?
• What can you do with what you learned about
  resistance in materials?

18
Make the Connection

• Use your multimeter to measure the resistance of
  your body from one hand to the other.
• Set the meter to 20M.
• Grab the tip of the red lead between two fingers
  in your right hand.
• Grab the tip of the black lead between two
  fingers in your left hand.
• Squeeze tightly, and note the resistance
  measurement on the readout.
• Record your measurement.
• What factors do you think cause the variations
  between the measurements of various people?

19
Make the Connection

• Now lick the four fingers you used to get them
  wet and repeat the measurement.
• 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?

20
Make the Connection

• What affects the resistivity of various
  materials?
• How might doping can change the resistance of
  materials?