Demonstration Device of an Alarm from a Clock Under a Bell

Product Code : SCL-PL-11839

Demonstration Device of an Alarm from a Clock Under a Bell (SKU SCL-PL-11839) is the classic bell-in-vacuum experiment: an electric bell rings inside a glass enclosure while a vacuum pump removes the air, and the sound fades even though the bell can still be seen working. It proves that sound needs a medium and suits Class 8–9 science and Class 11 physics. Science Lab Supplies, the manufacturer, assembles the set at Plot 448, HSIIDC Industrial Area, Saha, Ambala, India, supplying schools, colleges, tender contractors and distributors direct.

Specifications

The set brings together a glass cage to enclose the bell, an electric bell and its power source, a rubber plug fitted with two sockets so the bell can be wired from outside, a glass tube, one metre each of black and red connecting wire, and a vacuum pump to evacuate the enclosure.

Applications and Experiments for the Bell in Vacuum Demonstration

With the bell ringing inside the glass cage, the teacher runs the vacuum pump and the class hears the sound grow fainter as air is removed, then return when air is let back in. The demonstration shows that sound travels through a material medium and cannot cross a vacuum.

• Class 8 science: sound needs a medium to travel.
• Class 9 science: propagation of sound as a mechanical wave.
• Class 11 physics: introduction to mechanical waves.

An evacuated glass vessel is under pressure from outside air. Check the glass for cracks before each use, run the pump only under teacher supervision, and keep pupils at a safe distance.

Standard Scope of Supply

Each set is supplied with the glass cage, an electric bell, a rubber plug with two sockets, a glass tube, an electric power source, a 1 m black conductor wire, a 1 m red connecting wire and a vacuum pump. Optional extras, if needed, are shown on the quotation.

Packing, MOQ and Lead Time

Schools may request a quotation for one set or for several science rooms at once. Packing, delivery time and price are stated for that exact quantity, and other sound or pressure demonstrations from the physics lab equipment range can be quoted alongside.

Science Lab Supplies holds an Importer-Exporter Code, which means it can ship to buyers in Ethiopia, Tanzania, Uganda, the UAE, Saudi Arabia and Oman. Enquiries can be sent from the contact page or the enquiry cart; public-sector buyers will find the lab tender page useful.

Frequently Asked Questions

What does the bell under a glass cover demonstrate?
That sound needs air or another medium. As the pump removes air, the ringing fades although the bell keeps working, and the sound returns when air re-enters.

Is a vacuum pump included?
Yes. The set contains a vacuum pump along with the glass cage, electric bell, power source and connecting wires.

Is Science Lab Supplies the manufacturer or a trader?
Science Lab Supplies is a manufacturer with its own factory in Saha, Ambala, India. This demonstration set is assembled there, and enquiries are answered by the factory team.

Is the demonstration safe for a classroom?
Yes, when handled by a teacher. Inspect the glass before use, avoid knocking the evacuated cage and let air back in slowly after the demonstration.

Related Sound and Vacuum Equipment

These Physics Lab items pair well with the bell-in-vacuum set: spare bell jars, two vacuum pump options for other air-pressure demonstrations, and a further sound experiment. All four can be requested on the same quotation.

• Bell Jars — glass jars for vacuum demonstrations.
• Hand Vacuum Pump — a hand-operated pump option.
• School Vacuum-Pump Set — a vacuum pump set for air-pressure experiments.
• Law of Reflection of Sound Apparatus — the next sound topic.

Browse the full Physics Lab range or all physics lab equipment.

Last updated: 25 September 2026