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 manufactures the set at Plot 448, HSIIDC Industrial Area, Saha, Ambala, India, and the factory quotes schools, colleges, tender contractors and distributors itself.
Specifications
Each component of the bell-in-vacuum set is entered in its own row of the table. In short, a glass cage encloses an electric bell, a rubber plug with two sockets lets the bell be wired from outside, a glass tube and vacuum pump remove the air, and a power source with 1 m red and black wires drives the bell.
| Specification | Value |
|---|---|
| SKU | SCL-PL-11839 |
| Enclosure | Glass cage |
| Sound source | Electric bell |
| Seal | Rubber plug with two sockets |
| Glass tube | 1 |
| Power source | Electric power source |
| Black wire | 1 m |
| Red wire | 1 m |
| Evacuation | Vacuum pump |
| Manufacturer | Science Lab Supplies, Saha, Ambala, Haryana |
| Country of origin | India |
Applications and Experiments for the Bell in Vacuum Demonstration
With the bell ringing inside the glass cage, running the vacuum pump lets the class hear 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, after showing with a Tuning Fork Set that sound comes from vibrating objects.
- Class 9 science: propagation of sound as a mechanical wave, with the level outside the cage followed on a Digital Sound Meter.
- 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. To have the vacuum demonstration priced, contact the team via the contact page, place it in the enquiry cart with any pumps or jars, or follow the lab tender page for public tenders.
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, rubber plug with two sockets, glass tube, power source and the red and black connecting wires.
Is Science Lab Supplies the manufacturer or a trader?
The bell-in-vacuum set is manufactured and packed at the Science Lab Supplies factory in Saha, Ambala, India, and enquiries about it are answered by the same factory team, not by a trading house.
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 and Properties of Matter items pair well with the bell-in-vacuum set: other bell jars, pump options for further air-pressure demonstrations, the Magdeburg hemispheres and a sound-reflection experiment. All of them can be requested on the same quotation as this set.
- Bell Jars — baseplate with tap, glass bell jar and detachable battery-operated bell.
- Bell Experiment Apparatus — 2 litre bell jar with an electric bell hung from its stopper, for 3–6 V.
- Hand Vacuum Pump — draws 15 cm³ per stroke, to a maximum vacuum of 50 mmHg.
- Air Pump (Vacuum Pump with Aluminium Plate) — single steel barrel on a wooden base, plate with stopcock.
- School Vacuum-Pump Set — vacuum bell jar for boiling under reduced pressure and a vacuum fountain.
- Magdeburg Hemispheres — 62 mm or 75 mm cups with handles and a stopcock.
- Law of Reflection of Sound Apparatus — base plate for measuring incident and reflected angles of sound.
Browse the full Physics Lab range, the Properties of Matter range, or all physics lab equipment.
Last updated: 22 October 2026
