Post Office Box Manufacturer,Supplier and Exporter in India
Product Code : EL-PLE-10960
Quick Answer: The Post Office Box is a resistance box in plug type and dial type versions with constantan or manganin coils. The plug type has ratio coils of 10, 100 and 1000 ohms, a total of 11110 ohms and two tapping keys, for resistance measurement in school and college physics.
Last updated: October 2026
Key Features
- Plug type with constantan coils: three ratio coils of 10, 100 and 1000 ohms plus a series of 1 to 5000 ohms, total 11110 ohms
- Two tapping keys with silver contacts for the battery and galvanometer
- Interchangeable brass plugs with oval bakelite top
- Coils wound with double silk covered wire on bakelite bobbins, heat treated and aged
- Manganin coil versions in a polished teak wood box
- Dial type versions with 5 or 6 dials on an ebonite base
Technical Specifications
| Specification | Value |
|---|---|
| Coils | Constantan; manganin coil versions also listed |
| Ratio coils (plug type) | 10, 100 and 1000 ohms |
| Series (plug type) | 1 to 5000 ohms |
| Total resistance (plug type) | 11110 ohms |
| Plugs | Interchangeable brass plugs with oval bakelite top |
| Blocks | Standard size, corrosion resistant hard brass, golden lacquered |
| Keys | Two tapping keys with silver contacts |
| Dial type | Each dial covers a decade of resistance; 5 or 6 dials; ebonite base in a polished teak wood box |
About This Product
A post office box is a compact form of the Wheatstone bridge used to measure an unknown resistance. The ratio coils and the series of resistances are selected by removing plugs or by turning dials, and the tapping keys are pressed to connect the battery and the galvanometer. The box is balanced when the galvanometer shows no deflection. It is a standard instrument in school and college physics practicals on resistance measurement. Alongside supply within India, the Post Office Box is offered for export to Somalia, Turkey, Equatorial Guinea, Samoa, Mali and Venezuela.
Frequently Asked Questions
Q1. What resistance values does the plug type Post Office Box provide?
It has ratio coils of 10, 100 and 1000 ohms and a series of 1 to 5000 ohms, with a total of 11110 ohms.
Q2. How do the plug type and dial type differ?
The plug type uses interchangeable brass plugs. The dial type has a dial for each decade of resistance, with 5 or 6 dials, mounted on an ebonite base in a polished teak wood box.
Related: Physics Lab Equipment, Spot Reflecting Galvanometer, Ohm Meter, Multi-Range Meter.
For a quotation on the Post Office Box, contact School Lab Equipment India.