Physics Lab Worksheet

BCIT Department of Physics EMO-02

Version: Jun-23 - 1 - © Dr. M. Harder

EMO-02: DC Circuits

Learning Outcomes Through this exercise you will improve your ability to construct simple circuits, consisting of a single voltage source and one or more LEDs. You will also learn about key properties of LEDs, such as their voltage and current characteristics. Experimental Objectives The objective of this experiment is to light LEDs using various circuit configurations. Equipment

• Play-Doh • 9V Battery • 5 red (or yellow or orange) LEDs • 5 white (or blue or green) LEDs

Equipment Specifications • A small (125 mL) container of play-doh will suffice. This is usually available for

approximately $1 at most dollar stores. • Any 9V battery will do, though I would recommend against using a rechargeable

battery, as the Play-Doh may corrode the terminals. • Some options for purchasing LEDs

• Online retailers, e.g. Amazon bit.ly/3WVSNDm. Typically online retailers will sell more in 1 pack than you need, but they are still inexpensive and may be more convenient.

• Lee’s Electronic at 4131 Fraser Street in Vancouver (leeselectronic.com). Red LEDs https://bit.ly/3yRjXAd and green LEDs https://bit.ly/3VCvkpy

• SMI Electronics at 306-20560 Langley Bypass in Langley (https://www.smi- elec.com/). Red LEDs bit.ly/3NeWDnW and green LEDs bit.ly/42pe3T9

• RP Electronics at 8061 North Fraser Way in Burnaby (https://www.rpelectronics.com/) . Unfortunately LEDs listed in their online store will not be ideal for our experiments. But if this is a convenient location, you can purchase the cheapest red and green LEDs you can find from them and just use that.

• Note that shipping LEDs from local stores may be expensive. It would be better to pick them up in person. If you have any challenges sourcing the LEDs, please contact me as soon as possible.

EMO-02 BCIT Department of Physics

- 2 - © Dr. M. Harder

Theory

Diodes

A diode is an electrical device that only allows current to pass in one direction. More precisely, a diode makes it easy for current to pass in one direction, and difficult to pass in the other direction. This means that, depending on the polarity of the voltage we apply to a diode, it may act as a conductor or as an insulator! This is a very useful property, which may be used to perform rectification, the converting of ac signals to dc. More generally, diodes may be used as a component in logic gates, as temperature sensors, due to their non-linear current-voltage relationship, among other applications. Most diodes are now made using semiconductors, mainly silicon. For more information about diodes, see the Wikipedia article, https://en.wikipedia.org/wiki/Diode, or the following YouTube videos: http://bit.ly/3ENW8Nk; http://bit.ly/3OqLXRN. These references are for interest, and to deepen your understanding. They are not required to perform this experiment.

Light-Emitting-Diodes and Polarity

In our experiment, we will be using a light-emitting-diode, or LED. When current passes through LEDs, light is emitted. But since current can only pass in one direction, light will only be emitted when the LED is connected in the correct orientation! This is shown in Fig. 1 (b) and (c). So how should we connect an LED? One method is to just see what works. If the LED doesn’t light up, try switching the connections. However a more systematic way is also built into the LED design. One leg is longer than the other, and it is this longer leg that must be connected to the positive terminal of the battery in order to emit light.

Figure 1: (a) Diode circuit diagram, including a dc voltage source, current-limiting resistor, and diode. (b) Schematic diagram of the simple diode circuit, similar to one you will build during this exercise. This circuit has a 9 V battery and a 2.000 kΩ resistor. (c) A picture of the type of circuit you will make in this exercise. Since the play-doh is a non- ideal wire, which has resistance, we do not need to include a resistor to limit the current. Notice that the longer lead of the LED is connected to the positive terminal of the battery.

BCIT Department of Physics EMO-02

- 3 - © Dr. M. Harder

Light-Emitting-Diodes and Voltage

In order for an LED to emit light, not only does the polarity need to be correct, but we also need a sufficient voltage difference across the terminals. The voltage required depends on the type of LED, but is typically around 2.0 V for red, yellow or orange LEDs and around 3.0 V for white, blue or green LEDs. You will explore this difference during this exercise.

Light-Emitting-Diodes and Current

LEDs typically have very low resistance (in one direction) and can only handle small levels of current, on the order of 10 mA. For this reason a current-limiting resistor (i.e., a resistor that limits the current) is usually wired in series with an LED, as shown in Fig. 1 (a) and (b). Without this resistor the LED would overload and burn out. In the circuits we will make, the play-doh wire is non-ideal and has a fairly high resistance, of approximately 2 – 3 kΩ per 2 – 3 cm, although this value will vary depending on the play-doh and the diameter. Because of this inherent resistance in our wires, we do not need to add a separate current- limiting resistor. However, be careful not to directly connect the LED to the battery (at least not until you are finished your experiment) as this will burn out the LED.

Procedure

For this experiment, simply follow through the worksheet, completing the exercises as you answer the questions.

Note: Carefully read through the Theory section of this lab description to understand the relevant properties of LEDs, and what to avoid while performing your exercise. Also avoid direct play-doh contact between the terminals of your battery. This will cause the battery to drain very fast.

Worksheet

Complete the EMO-02 worksheet on separate sheets of paper. See Sec. 9 of the lab manual introduction for creating and combining PDFs. Submit your PDF to the appropriate Learning Hub Assignment folder.

BCIT Department of Physics EMO-02 - Worksheet

Version: Nov-22 - 1 - © Dr. M. Harder

EMO-02: DC Circuits – Worksheet

Maximum Score: 20 1. [2] Construct a circuit to light a single LED. Attach a picture of your circuit, and draw a

circuit diagram. 2. [2] Change the polarity of your LED, in other words, change the direction of the Play-Doh

wire connection to your LED. What do you observe? Explain your observation. 3. [2] Connect three red LEDs in series. Observe the brightness of the LEDs. Attach a

picture of your circuit, and draw a circuit diagram. 4. [2] Connect three red LEDs in parallel. Observe the brightness of the LEDs. Attach a

picture of your circuit, and draw a circuit diagram. 5. [2] Based on your observations, are the LEDs brighter in series or in parallel? Explain why

you observe this behaviour. 6. [2] Build a circuit with three red LEDs in parallel using thin wires, and then build a circuit

with three red LEDs using much thicker wires. What observations do you make regarding the brightness in these two circuits. Explain your observation.

7. [1] How many red LEDs can you connect in series, with the LEDs still lighting?

8. [1] How many red LEDs can you connect in parallel, with the LEDs still lighting?

9. [1] Explain the difference between your answer to Question 7 and Question 8.

10. [1] How many white LEDs can you connect in series, with the LEDs still lighting?

11. [1] Explain the difference between your answer to Question 7 and Question 10.

12. [3] Try something else with your circuit, and tell me about it!

BCIT Department of Physics EMO-02

Version: Jun-23 - 1 - © Dr. M. Harder

EMO-02: DC Circuits

Learning Outcomes Through this exercise you will improve your ability to construct simple circuits, consisting of a single voltage source and one or more LEDs. You will also learn about key properties of LEDs, such as their voltage and current characteristics. Experimental Objectives The objective of this experiment is to light LEDs using various circuit configurations. Equipment

• Play-Doh • 9V Battery • 5 red (or yellow or orange) LEDs • 5 white (or blue or green) LEDs

Equipment Specifications • A small (125 mL) container of play-doh will suffice. This is usually available for

approximately $1 at most dollar stores. • Any 9V battery will do, though I would recommend against using a rechargeable

battery, as the Play-Doh may corrode the terminals. • Some options for purchasing LEDs

• Online retailers, e.g. Amazon bit.ly/3WVSNDm. Typically online retailers will sell more in 1 pack than you need, but they are still inexpensive and may be more convenient.

• Lee’s Electronic at 4131 Fraser Street in Vancouver (leeselectronic.com). Red LEDs https://bit.ly/3yRjXAd and green LEDs https://bit.ly/3VCvkpy

• SMI Electronics at 306-20560 Langley Bypass in Langley (https://www.smi- elec.com/). Red LEDs bit.ly/3NeWDnW and green LEDs bit.ly/42pe3T9

• RP Electronics at 8061 North Fraser Way in Burnaby (https://www.rpelectronics.com/) . Unfortunately LEDs listed in their online store will not be ideal for our experiments. But if this is a convenient location, you can purchase the cheapest red and green LEDs you can find from them and just use that.

• Note that shipping LEDs from local stores may be expensive. It would be better to pick them up in person. If you have any challenges sourcing the LEDs, please contact me as soon as possible.

EMO-02 BCIT Department of Physics

- 2 - © Dr. M. Harder

Theory

Diodes

A diode is an electrical device that only allows current to pass in one direction. More precisely, a diode makes it easy for current to pass in one direction, and difficult to pass in the other direction. This means that, depending on the polarity of the voltage we apply to a diode, it may act as a conductor or as an insulator! This is a very useful property, which may be used to perform rectification, the converting of ac signals to dc. More generally, diodes may be used as a component in logic gates, as temperature sensors, due to their non-linear current-voltage relationship, among other applications. Most diodes are now made using semiconductors, mainly silicon. For more information about diodes, see the Wikipedia article, https://en.wikipedia.org/wiki/Diode, or the following YouTube videos: http://bit.ly/3ENW8Nk; http://bit.ly/3OqLXRN. These references are for interest, and to deepen your understanding. They are not required to perform this experiment.

Light-Emitting-Diodes and Polarity

In our experiment, we will be using a light-emitting-diode, or LED. When current passes through LEDs, light is emitted. But since current can only pass in one direction, light will only be emitted when the LED is connected in the correct orientation! This is shown in Fig. 1 (b) and (c). So how should we connect an LED? One method is to just see what works. If the LED doesn’t light up, try switching the connections. However a more systematic way is also built into the LED design. One leg is longer than the other, and it is this longer leg that must be connected to the positive terminal of the battery in order to emit light.

Figure 1: (a) Diode circuit diagram, including a dc voltage source, current-limiting resistor, and diode. (b) Schematic diagram of the simple diode circuit, similar to one you will build during this exercise. This circuit has a 9 V battery and a 2.000 kΩ resistor. (c) A picture of the type of circuit you will make in this exercise. Since the play-doh is a non- ideal wire, which has resistance, we do not need to include a resistor to limit the current. Notice that the longer lead of the LED is connected to the positive terminal of the battery.

BCIT Department of Physics EMO-02

- 3 - © Dr. M. Harder

Light-Emitting-Diodes and Voltage

In order for an LED to emit light, not only does the polarity need to be correct, but we also need a sufficient voltage difference across the terminals. The voltage required depends on the type of LED, but is typically around 2.0 V for red, yellow or orange LEDs and around 3.0 V for white, blue or green LEDs. You will explore this difference during this exercise.

Light-Emitting-Diodes and Current

LEDs typically have very low resistance (in one direction) and can only handle small levels of current, on the order of 10 mA. For this reason a current-limiting resistor (i.e., a resistor that limits the current) is usually wired in series with an LED, as shown in Fig. 1 (a) and (b). Without this resistor the LED would overload and burn out. In the circuits we will make, the play-doh wire is non-ideal and has a fairly high resistance, of approximately 2 – 3 kΩ per 2 – 3 cm, although this value will vary depending on the play-doh and the diameter. Because of this inherent resistance in our wires, we do not need to add a separate current- limiting resistor. However, be careful not to directly connect the LED to the battery (at least not until you are finished your experiment) as this will burn out the LED.

Procedure

For this experiment, simply follow through the worksheet, completing the exercises as you answer the questions.

Note: Carefully read through the Theory section of this lab description to understand the relevant properties of LEDs, and what to avoid while performing your exercise. Also avoid direct play-doh contact between the terminals of your battery. This will cause the battery to drain very fast.

Worksheet

Complete the EMO-02 worksheet on separate sheets of paper. See Sec. 9 of the lab manual introduction for creating and combining PDFs. Submit your PDF to the appropriate Learning Hub Assignment folder.