Robotics 2 - Lesson 2: Light Dependent Resistors

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Questions and Answers

What is another common name for a light dependent resistor?

  • Capacitor
  • Thermistor
  • Photocell (correct)
  • Inductor

How does the resistance of an LDR change as light intensity increases?

  • Resistance increases linearly
  • Resistance remains constant
  • Resistance increases exponentially
  • Resistance decreases (correct)

What type of material is primarily used in manufacturing LDRs?

  • Superconductors
  • Insulators
  • Conductors
  • Semiconductors (correct)

Which characteristic is associated with placing an LDR in complete darkness?

<p>High resistance (D)</p> Signup and view all the answers

Which of the following applications commonly use Light Dependent Resistors?

<p>Automatic Street lights (B)</p> Signup and view all the answers

What is a notable disadvantage of using LDRs?

<p>Highly inaccurate response time (A)</p> Signup and view all the answers

Within the context of fire alarms, what is the role of the LDR?

<p>To detect the absence of light due to smoke. (D)</p> Signup and view all the answers

What does it mean that LDRs are considered to be non-linear devices?

<p>Their sensitivity varies with the wavelength of light (B)</p> Signup and view all the answers

Flashcards

What is a Light Dependent Resistor (LDR)?

A light-sensitive resistor whose resistance decreases as the intensity of light falling on it increases.

What are the characteristics of LDRs?

LDRs are made of semiconductor materials with high resistance in the dark. Their sensitivity varies depending on the color of light, and they may not respond to certain wavelengths.

What is the 'dark resistance' of an LDR?

The resistance of an LDR in complete darkness; it can be very high, around 10^12 Ohms.

Explain 'photoconductivity' in LDRs.

The principle that a light-dependent resistor's resistance decreases as the intensity of light increases.

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How are LDRs used in automatic streetlights?

Automatic streetlights use LDRs to sense ambient light levels, switching on at dusk and off at dawn.

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How are LDRs used in fire alarms?

LDRs can be used to detect fire. If smoke blocks the light reaching the LDR, its resistance increases, triggering an alarm.

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What are the advantages of using LDRs?

Small, inexpensive, and readily available in various sizes and shapes. They consume little power and operate on low voltage.

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What are the disadvantages of using LDRs?

They are not very precise in their response and have a relatively slow reaction time, typically in the range of tens to hundreds of milliseconds.

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Study Notes

Robotics 2 - Lesson 2: Light Dependent Resistor

  • This lesson covers light dependent resistors (LDRs), also known as photoresistors or photocells
  • LDRs are variable resistors controlled by light
  • Their resistance changes based on light intensity

Target

  • Students should be able to define LDRs
  • Students should be able to identify the working principle and characteristics of LDRs
  • Students should be able to create projects utilizing LDRs

Light Dependent Resistor (LDR) Characteristics

  • LDRs are made of semiconductor materials with high resistance
  • LDRs are non-linear devices
  • The sensitivity of LDRs varies with the wavelength of incident light
  • Some photocells may not respond to certain wavelengths

Applications of LDR

  • LDRs are used in various devices, such as automatic streetlights, camera light sensors, and solar panels
  • LDRs enable automatic light detection and contribute to energy-saving applications
  • Light sensors utilizing LDRs activate LEDs when sufficient light reaches the LDR
  • Fire alarms use LDRs to detect smoke by sensing the change in light intensity caused by smoke
  • Automatic streetlights use LDRs; they turn on at night and off during the day

LDR Characteristics: Photoconductivity

  • As light intensity increases, LDR resistance decreases
  • LDR resistance is very high when kept in the dark. This is known as dark resistance
  • Dark resistance can be as high as 1012 Ohms

LDR Advantages

  • LDRs are inexpensive and readily available in various sizes and shapes
  • They require minimal power and voltage for operation

LDR Disadvantages

  • They are relatively inaccurate
  • Response time of about tens or hundreds of milliseconds

Activity 2: Light Dependent Resistor

  • The activity involves building and coding a circuit with an LDR and an LED to react to light changes

Target - Activity 2

  • Students at the end of this part should be able to build and input code to their systems based on provided circuit diagrams

Materials - Activity 2:

  • The presentation displays images of components, indicating various materials required for the activity (e.g. Arduino board, resistors, wires, LDR).

Code for Activity 2: Light Dependant Resistor

  • The presentation contains Arduino code for the activity

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Related Documents

Robotics 2: LDR, Lesson 2, PDF

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