EXPERIMENT 103. To study the construction and use of a simple "current reverser."
Apparatus. A dry cell, D C (No. 51); a compass, O C (No. 18); a current reverser, C R (No. 57) (See [§ 235]); an insulated copper wire, C W, 2 or 3 feet long, with spring connectors joined to its ends ([§ 226]).
Arrange as in [Fig. 70]. The wire, C W, leading from X should be held by the left hand so that it will be just above (or below) and parallel to the magnetic needle.
The current cannot pass through C W until one of the straps or levers on C R is pressed. (See Apparatus Book for Home-Made Reversers.)
235. The Current Reverser. (No. 57.) To the wooden base ([Fig. 69]) are fastened four metal straps, each turned up at the end so that spring connectors ([§ 227]) can be slipped on to make electric connections with other pieces of apparatus.
Suppose that at C and Z connections are made with the carbon and zinc of the cell, by means of wires and spring connectors ([§ 226]). The current comes from the cell to C. As the two straps, 2 and 3, press firmly up against strap 4, and do not touch 1, it is evident that no current can pass from 1 to 2 or to 3 until they are pressed down upon 1. Two wires are joined by spring connectors to 2 and 3 at their turned up ends, X and Y, and these wires lead to any desired instrument.
236. Directions. (A) Press down lever 2 ([Fig. 70]), for an instant only, at the same time noting carefully in which direction the N pole of the needle is deflected.
(B) After allowing lever 2 to spring up again, and after the needle comes to rest, press down lever 3 for an instant, watching the needle. Is the N pole of the needle deflected in the same direction as it was in (A)?