Investigation 2

Part 1

 This is a new component you will be investigating today.  The schematic symbol for a resistor is

 Resistors are used in some circuits. Work with your partner to find out what resistors do when they are placed in a circuit along with other components – battery, switch, lamps.  Getters – get your springboard bag and 1 resistor from each of the 4 cups.  Update your inventory card to include the 4 resistors.

 Some resistors conduct electricity and others do not. (Actually, all resistors conduct electricity, but not enough to light the lamp.)  All resistors in series with lamps make the lamp grow dimmer.  Each different resistor in series with a lamp makes it glow with a different brightness.  Some resistors in parallel with lamps make the lamp dim a tiny bit; some resistors in parallel with lamps don’t affect the brightness of the lamps.  Some resistors get warm when they are in parallel with a lamp.

 The resistors make the lamps dimmer. How can you explain this observation.  What do you think is happening inside the resistor to cause the lamp to burn with such reduced intensity?

 Are these statements accurate? ◦ Resistors push back on electricity. ◦ Resistors use up electricity. ◦ Resistors slow down electricity. ◦ Resistors clog up the circuit. ◦ Electricity gets stuck in resistors.

 Read the sequence of colored bands on one of the resistors starting at the end that is NOT gold.  These color bands are the “names” of the resistors. One resistor is named orange/orange/brown. What are some of the other names?

 Which resistor allowed the lamp to glow the brightest? ◦ Violet/green/black  Which resistor allowed the lamp to glow the dimmest? ◦ Brown/black/red  Put the resistors in order from brightest to dimmest. ◦ Violet/green/black ◦ Brown/green/brown ◦ Orange/orange/brown ◦ Brown/black/red

 Be sure to put your resistor investigation records in a safe place – you will need them for the next investigation.  Return and inventory all components to the components bag.  Secure battery leads.  Return all materials to the table.

Part 2

 Were all four of your resistors the same?  How do you know they are different?  What is one way to tell resistors apart by looking at them?

 Resistors are different from one another. Some make lamps glow dimly. Others let lamps glow brightly. Different resistors have different amounts of resistance. Some resistors have a lot of resistance while others have very little resistance.  Resistance is measured in units called ohms.  The symbol for the ohm is the Greek letter omega (Ω). For instance, a resistor with a resistance of 100 ohms is written 100Ω.

 Which resistor has the greatest resistance?  Which resistor has the least resistance?  How do you know?

 What is a code?  The color bands on the resistors are a code that tells the resistance of each resistor.  The resistance can be anywhere from 1 ohm to several million ohms.

 Each of the 10 colors used in the code represents a different numeral from zero to nine.  Read the code starting at the end opposite the gold band.  Band 1 is a number and band 2 is a number, but band 3 is the number of zeros to add after the first two numbers.

 Lab book – Resistor Investigation  Look at the 6 hypothetical resistors at the bottom of the sheet.  Decode the resistors – 3 minutes

 Red/green/brown – 250 Ω  Grey/black/black – 80 Ω  Yellow/blue/green – 4,600,000 Ω  Black/orange/black – 3 Ω  Violet/black/red – 7000 Ω  Brown/red/orange – 12,000 Ω

 Decode the resistors in your bags.  Write the ohm values on the line beside the color codes (3 minutes).  Answers: ◦ Violet/green/black – 75 Ω ◦ Brown/green/brown – 150 Ω ◦ Orange/orange/brown – 330 Ω ◦ Brown/black/red – 1000 Ω

 What is the relationship between the amount of resistance in the circuit and the brightness of the lamp?  Answer – there is an inverse relationship between brightness and resistance in a series circuit.

 Create a color code card for identifying resistors.  Keep it in you binder.

Part 3

 When scientists, engineers and technicians who work with electricity need accurate information about what is going on with a circuit, they use a meter.  ltimedia/Electronics/content/co_mu_in_274_ 1.htm ltimedia/Electronics/content/co_mu_in_274_ 1.htm

They are precision instruments and must be handles with care.

 There can not be any electricity flowing through a component when you are measuring resistance. Resistance is measured in components when they are NOT part of a circuit. If electricity flows to the probes when you are measuring resistance, the meter will be damaged.  NEVER attempt to measure the resistance of a battery – it will damage the meter.  Turn meters OFF before storing them at the end of class.

Probe Display Screen Rotary Switch

Rotate the switch to 2000 Ω. The number 1 in the display indicates the meter is ready to measure resistance. Touch the 2 probes together at the tips. The 0 indicates the meter is reporting no resistance.

 Review Resistor Accuracy – the gold band is the manufacturer’s way of telling us the resistor is no more than plus or minus 5% of the claimed value. 100 Ω

 How could you test your resistors to see if they are accurate?  Record your measured resistances on the Resistor Investigation Sheet.  What is the resistance of a piece of wire?  Write down its band code.  What is the resistance of a lamp?  Write down its band code.

 Wire – black/black/black0 Ω  Lamp – red/black/black20 Ω

 Compute the percentage of error for each of the 4 resistors.  Add a fourth column to page 7 and record your % error there.  Are they within the 5% acceptable range?

Part 4

 Has 2 wires that can be used to connect it in a circuit with other components.  Your job is to figure out what it does in a circuit.

 DO NOT connect the potentiometer to the battery itself. Use it only in a series with other components.

 The potentiometer can turn the light off or make it very bright.  It can make the light dimmer or brighter.  It acts like a changeable resistor.  It is like a volume control for a light.

 The potentiometer is a resistor that can be changed by turning the wheel.  They are used in a variety of situations. ◦ Light dimmers ◦ Volume controls on audio devices ◦ Speakers balance adjusters

 What do you think might be inside a potentiometer that would produce the variable resistance?  Why do you think you were cautioned not to connect the potentiometer to the battery?

 What is the MOST resistance and the LEAST resistance the potentiometer can impose on a circuit?  REMEMBER to remove the potentiometer from the circuit BEFORE testing its range.