Post Office Box (PO Box) for Physics Practical

A post office box is a compact form of Wheatstone’s bridge. A Post Office Box can also be used to measure an unknown resistance. It is a Wheatstone Bridge with three arms, P, Q, and R, while the fourth arm is the unknown resistance. P and Q are known as the ratio arms, while R is known as the rheostat arm.

Post Office Box (PO Box) for Physics Practical Class & Exam

Plug-in type. The heavy brass contact blocks are bonded to the vulcanite by a double nut system. The plugs & lugs are cut to a finer taper & are interchangeable. The plug heads are machine-molded of bakelite.

Each resistor is independently mounted with double leads. The accuracy of Constantan coils is 0.1% for lower values & 0.5% for higher values. Resistor: the best-imported constant wire is wound on ebonite spools; the method adopted is non-inductive & non-magnetic. Each resistor is dipped in boiling wax. Provided as above with 3 ratio coils of 1000, 100 & 10 ohms. Rheostat arm 15,000 ohms. Two tapping keys with silver contacts are provided for the battery & galvanometer in a teakwood case with a hinged lid.

• Overall dimensions: 280x200x175mm approx.
• Premium Quality PO Box
• Made in India