An ideal solution to the common physics experiment demonstrating that sound will not travel in a vacuum.

Place the bell jar on the pump plate, briefly connect the power supply. The bell can be heard ringing. Connect the vacuum pump to the pump plate and evacuate as much air as possible. Close the valve, switch off the pump and connect the power again. The bell striker moves but can barely be heard. Open the valve slowly, allowing air back in, and the volume of the bell increases.

The apparatus consists of:

A sturdy metal base plate mounted on a metal tripod:

Baseplate dimensions:

Height: 200mm

Diameter: 230mm

The bell jar comes complete with an electric bell that requires a suitable d.c. power supply (3–6V). Connection to a power supply is made via two 4mm terminals that protrude from the rubber stopper positioned at the top of the bell jar.

Bell jar dimensions

Height: 260mm

Diameter: 180mm

Overall mass: 5kg.