| 摘要 |
1,224,414. Teaching aids. RICOH K.K. 29 May, 1969 [4 June, 1968; 20 June, 1968], No. 27265/69. Heading G5G. A teaching aid installation includes a D.C. source whose polarity may be reversed (by a teacher) by means of a switch S 2 and which is connected to each of a plurality of switch units (one for each student) S 21 , S 22 &c. Each student's switch unit has either (as shown) two rectifiers a, b and one switch c or (Fig. 3, not shown) two switches and one rectifier. In each case the switch or switches are three-position switches such that the unit can be set to pass D.C. of one polarity or the other or (in a neutral position of the switch in which it is disconnected from the source) neither. When the teacher asks a question, students who give a "YES" answer will light their respective indicators L 21 , L 22 &c. and students who have given a "NO" answer can be identified by the teacher reversing his polarity. Students who have declined to answer can also be identified, since their indicators will not be lit for either polarity of the teacher's switch. |
