Login or Register

800.334.5551 Live Chat

Energy Transformations in a Dark Detector

A Carolina Essentials™ Activity
electronic circuit testing on bread board

Overview

This activity is designed to give students the opportunity to design, build, and test a dark detector circuit. A dark detector is a simple circuit that can be used to explain the function of a light-dependent resistor and a transistor, two common electrical components. The theory of how the sensor works was developed by Max Planck, the father of quantum mechanics. Albert Einstein provided the explanation for Max Planck’s theory, which became the Nobel Prize winning photoelectric effect explanation.

Photocells such as the light dependent resistor (LDR) used in this activity operate on the photoelectric effect. When particles or quanta of light, known as photons, with sufficient energy, strike the surface of certain semiconducting materials, the energy of the photons is transferred to electrons causing them to be ejected from the surface atoms of the semiconductor. When the semiconductor is used to construct a photocell, and a voltage is applied to the photocell, the electrons move, and current flows through the circuit.

Photocells, such as the light dependent resistor in the dark detector circuit, function as transducers, converting light in the form of radiant energy into electrical energy through the photoelectric effect. Students will determine the maximum amount of light under which the dark detector will work and identify each point of energy transformation in the dark detector circuit.

Save & Print
Teacher Notes
Save & Print
Student Worksheet
electronic circuit testing on bread board
Grade & Discipline
9-12

Physical Science-Physics
Recommended for grades 9-12.

Time Requirements
Prep15 min
Activity30-45 min

Teacher Prep time: 15 min
Student Activity: 30-45 min

Safety Requirements
No PPE is required for the activity.

Overview

This activity is designed to give students the opportunity to design, build, and test a dark detector circuit. A dark detector is a simple circuit that can be used to explain the function of a light-dependent resistor and a transistor, two common electrical components. The theory of how the sensor works was developed by Max Planck, the father of quantum mechanics. Albert Einstein provided the explanation for Max Planck’s theory, which became the Nobel Prize winning photoelectric effect explanation.

Photocells such as the light dependent resistor (LDR) used in this activity operate on the photoelectric effect. When particles or quanta of light, known as photons, with sufficient energy, strike the surface of certain semiconducting materials, the energy of the photons is transferred to electrons causing them to be ejected from the surface atoms of the semiconductor. When the semiconductor is used to construct a photocell, and a voltage is applied to the photocell, the electrons move, and current flows through the circuit.

Photocells, such as the light dependent resistor in the dark detector circuit, function as transducers, converting light in the form of radiant energy into electrical energy through the photoelectric effect. Students will determine the maximum amount of light under which the dark detector will work and identify each point of energy transformation in the dark detector circuit.

Save & Print
Teacher Notes
Save & Print
Student Worksheet

Phenomenon

Ask students to explain how street lights “know” when to come on and turn off? Have they seen street lights come on during the day? During storms? Going off during bright lightning storms?

Essential Question

What is required to design and build a device that can convert one form of energy to another?

Activity Objectives

  1. Design and build a simple circuit that converts light (radiant) energy to electrical energy.
  2. Explain the energy transformations occurring in the dark detector.

Next Generation Science Standards* (NGSS)

HS-PS3-3. Design, build, and refine a device that works within given constraints to convert one form of energy into another form of energy.

Science and Engineering Practices

Constructing Explanations and Designing Solutions

  • Design, evaluate, and/or refine a solution to a complex real-world problem based on scientific knowledge, student-generated sources of evidence, prioritized criteria, and tradeoff considerations.

Disciplinary Core Ideas

PS3.A: Definitions of Energy

  • At the macroscopic scale, energy manifests itself in multiple ways, such as in motion, sound, light, and in thermal energy.

Crosscutting Concepts

Energy and Matter

  • Changes of energy and matter in a system can be described in terms of energy and matter flows into, out of and within that system.

Safety Procedures and Precautions

Work on a clean, dry surface. Check batteries for signs of corrosion. If corrosion is apparent, dispose or recycle the batteries properly.

Teacher Preparation and Disposal

If kits are not purchased, sort the necessary components for the dark detector into group baskets.

All materials can be reused.

Student

Teacher

  1. Student: Identify all the parts in the kit package.
  1. Teacher: If you are using individual components and not the kit, sort the components into a basket for students to ensure they have all the correct parts.
  1. Build the circuit using the schematic and wire diagram shown below:
circuit diagram illustration
  1. Emphasize placing all components into the bread board securely and in the proper location.
  1. Check the circuit by placing your hand over the light dependent resistor. If the LED did not come on, check that each component is securely in the bread board and in the current location.
  1. Place the flashlight on the construction paper and draw a circle around the light end. Cut out the circle ¼ in larger than you drew.
  1. You can pre-cut flashlight covers prior to the activity to save time.
  1. Turn on the flashlight. Dim or turn off the lights in the room.
  1. Working in a dimly lit to dark room enhances the effect of the LED intensity and ensures accurate observations.
  1. Shine the flashlight without the paper circle cover and record the intensity of light from the LED bulb.
  1. Use the paper cover to block ¼ of the flashlight and repeat the observation.
  1. Use the paper cover to block ½ of the flashlight and repeat the observation.
  1. Students observing the experiment should record the data in their notebooks.
    You may choose to assign additional students to record data on a whiteboard or laptop, or to use a probe or video recorder.
  1. Use the paper cover to block ¾ of the flashlight and repeat the observation.
  1. Use the paper cover to block all the flashlight and repeat the observation.

Data and Observations

Student answers will vary depending on the ambient light in the room. The LED will be on when no light is present. It may be on if there is very dim, ambient light in the room or when 75% of the flashlight is covered. Maximum flashlight light will not result in the LED turning on.


student graph of observations of a dark detector

Analysis & Discussion

1. Using the circuit diagram, label each point at which an energy transformation takes place and identify the specific transformation. Begin with the batteries.

Refer to the web resource “Demonstrating a Dark Detector.”

illustration of a labeled circuit diagram

2. Using your observations, explain why light levels affected when the circuit LED came on. How can these results be used to explain street light behavior?

The LED activates when current flows through the transistor’s collector to the emitter. This happens when sufficient current flows through the transistor’s base to the emitter. Current flows into the base when the resistance of the light dependent resistor, the LDR, increases, which happens when the amount of light shining on the LDR decreases.

Street lights must work the same way. For example, on a stormy night, lightning produces enough light to increase resistance, turning off the street lights. Also, as the amount of day light changes throughout the year, lights come on at different times but always when the light intensity reaches a minimum threshold.

*Next Generation Science Standards® is a registered trademark of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of, and do not endorse, these products.

Carolina Kits | 3D - Explore Kit Solutions for 3-Dimensional Learning. - Explore

You May Also Like