📄 PHYSICS PROJECT
NAME
AARUSH GUPTA
CLASS & SECTION
XII F
ROLL NO
TOPIC
FIRE ALARM
DATE OF SUBMISSION
01-07-2025
TEACHER’S NAME
MS. JUGNU JAIN
TEACHER’S SIGNATURE
TEACHER’S REMARKS
📜 Certificate
This is to certify that Aarush Gupta, a student of class XII-F, Presidium,
Indirapuram has successfully completed the coursework of Physics, titled
“Fire Alarm” under the guidance of Mrs. Jugnu Jain during 2025-26, in
partial fulfilment of the Physics practical examination of the Central Board of
Secondary Education.
Signature of Internal Examiner:
Signature of External Examiner:
🙏 Acknowledgement
I would like to express my heartfelt gratitude to our Vice Principal Ma’am,
Ms. Manvinder Kaur, for encouraging us to achieve excellence. My special
thanks to my Physics teacher Mrs. Jugnu Jain for her guidance, motivation,
and support throughout this project. I also thank Mr. Mahesh Kumar for his
help in the Physics Lab, and finally my family and friends for their support
during the preparation of this project.
📑 INDEX
S. No TOPIC Page Number
1 Certificate 2
2 Acknowledgement 3
3 Aim of the project 5
4 Introduction 6
5 Theory 7
6 Apparatus required 10
Circuit diagram 11
7 Procedure 12
8 Observation 13
9 Precautions and 14
sources of error
10 Bibliography 15
🎯 AIM OF THE PROJECT
The aim of the project is to study and demonstrate the working of a
basic fire alarm system.
📖 INTRODUCTION
A fire alarm is an electronic device that senses the presence of fire (usually
by detecting heat or smoke) and alerts people through visual and audio
signals. Fire alarms are essential safety devices used in homes, schools,
offices, and public places to prevent fire hazards and reduce damage.
The modern fire alarm systems typically use temperature sensors
(thermistors), smoke detectors, or gas sensors to detect signs of fire.
⚙️THEORY
Fire alarms generally work on two principles:
✅ Heat detection: Using temperature-sensitive components like thermistors
that change resistance with temperature rise.
✅ Smoke detection: Using smoke sensors that detect particles produced by
fire.
In this project, we use a thermistor that senses heat. When the temperature
increases beyond a certain level, the thermistor’s resistance drops,
triggering the circuit to activate an alarm buzzer.
Thermistor working principle: - A thermistor is a temperature-sensitive
resistor. - In Negative Temperature Coefficient (NTC) thermistors, the
resistance decreases as temperature increases. - When fire occurs, heat
increases → thermistor’s resistance drops → voltage across the thermistor
changes → comparator detects this and triggers buzzer.
🧰 APPARATUS REQUIRED
Thermistor (NTC type)
LM358 comparator IC
Alarm buzzer
10 kΩ resistor
330 Ω resistor
0.1 µF capacitor
Connecting wires
9V battery and battery clip
🔧 CIRCUIT DIAGRAM
(Attach or draw a simple circuit diagram showing thermistor connected to
comparator, which is connected to buzzer)
📝 PROCEDURE
1. Connect the thermistor in the voltage divider circuit along with a
resistor.
2. Connect the output of the voltage divider to the non-inverting terminal
of LM358.
3. Connect the inverting terminal to a preset potentiometer to adjust the
reference voltage.
4. Connect the output of the LM358 to an alarm buzzer.
5. When temperature is normal, thermistor resistance is high, output
remains low → buzzer OFF.
6. When fire raises temperature, thermistor resistance drops, voltage
changes, comparator output goes high → buzzer ON.
🔍 OBSERVATION
Under normal temperature, the buzzer remains OFF.
When the temperature near the thermistor increases (e.g., by bringing
a candle flame closer), the buzzer is triggered, indicating the presence
of fire.
⚠️Precautions and sources of error
Precautions - Avoid keeping the thermistor too close to an open flame to
prevent damage. - Ensure all connections are tight and insulated. - Adjust
the potentiometer carefully to set the correct threshold temperature.
Sources of error - External temperature fluctuations may trigger false
alarms. - Loose connections or faulty components may prevent the alarm
from working properly.
📚 BIBLIOGRAPHY
https://en.wikipedia.org/wiki/Fire_alarm_system
https://www.elprocus.com/fire-alarm-circuit-working-and-applications/
