Quick Answer:The Tapping Key is a normally open, momentary-contact switch: the circuit closes only while the insulated knob is pressed and opens as soon as it is released. It is used for bridge balancing, induction experiments and any reading that needs current for a moment only.
Last updated: 18 October 2026
Key Features
Momentary contact, normally open.
Spring-tempered contact arm returns the key to open.
Large-area contacts to reduce sparking.
Two terminals for connection.
Insulated moulded knob.
Technical Specifications
Specification
Value
Type
Momentary contact, normally open
Contact arm
Spring-tempered
Contacts
Large-area, to minimise sparking
Terminals
Two
Knob
Insulated, moulded
How It Is Used
The key is wired in series with the part of the circuit that should carry current only briefly, such as the galvanometer branch of a bridge or a coil in an induction experiment. Pressing the knob closes the circuit for the reading and releasing it opens it again.
Frequently Asked Questions
How does the Tapping Key differ from a toggle switch?
It needs continuous pressure to stay closed and opens as soon as it is released, so current flows only for the moment it is pressed.
