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LDR
An LDR is a light-dependent resistor whose resistance decreases as light intensity increases and rises in darkness.
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LDR
An LDR is a resistor that notices light.
Bright → low resistance.
Dark → high resistance.
Recommended for Class 10
LDR
An LDR, or light-dependent resistor, is a component whose resistance changes with light intensity.
For a typical LDR:
more light → lower resistance
less light → higher resistance
How It Is Used
An LDR can act as a light sensor.
It is often placed in a potential-divider circuit so that changing light intensity produces a changing output voltage.
Applications
Examples include:
automatic lighting; light-sensitive alarms; brightness-control systems; light-level sensing.
Example
During daylight, an LDR receives strong light and its resistance falls.
In darkness, its resistance rises.
A control circuit can detect this change and switch another device accordingly.
LDR — Advanced
An LDR is a photoconductive component. Incident light increases the availability of mobile charge carriers, reducing resistance.
Common Mistakes
Common Mistakes
- Mistake
Mistake: LDR directly produces darkness. Correction: LDR does not directly "produce darkness".
- Mistake
Mistake: LDR is not a sensor. Correction: It changes resistance in response to light.
Revision Zone
60-Second Revision
Quick cues from this topic — use them for last-minute revision.
Light ↑ → LDR resistance ↓.
Light ↓ → resistance ↑.
- Definition
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Practice
PQ
Q1. Define LDR.
PQ
Q2. State bright-light response.
PQ
Q3. State dark response.
PQ
Q4. Give an application.
PQ
Q5. Explain potential divider role.
Exam Practice
EQ
Q1. Explain operation of LDR.
EQ
Q2. State resistance-light relationship.
EQ
Q3. Give two applications.
EQ
Q4. Explain an automatic light system conceptually.
EQ
Q5. Explain why LDR is a sensor.
School-standard facts for Matric and Intermediate. Original explanations — not copied from textbooks.