Electrical measurementsA laboratory manual . ts of observations mthout x, and with re-sistances Bi and Bo in the box, of such value that the twodeflections 0^ and 6.^ sliall be respectively about 30° and 60°. Then ^ =7l tang(9i, or ~ cote, = B+ G + B,; (1) B+ a + B, ^ A ^^—^-^ = ^tang ^„ or|cot 6., = B+ (7+ B,. (2) Subtract (2) from (1) and ^ (cot d,-cot 6-?^ = B,-B,. ... (3) Then with x in circuit and a resistance B such thatthe deflection 6 may be intermediate between 6i and 62,we have ^ cote = B+ a+x-^B (4) Subtract (2) from (4) and ^ (cot 0 - cot ) =x + B -B,... (5) From (3) and (5) x-\
Electrical measurementsA laboratory manual . ts of observations mthout x, and with re-sistances Bi and Bo in the box, of such value that the twodeflections 0^ and 6.^ sliall be respectively about 30° and 60°. Then ^ =7l tang(9i, or ~ cote, = B+ G + B,; (1) B+ a + B, ^ A ^^—^-^ = ^tang ^„ or|cot 6., = B+ (7+ B,. (2) Subtract (2) from (1) and ^ (cot d,-cot 6-?^ = B,-B,. ... (3) Then with x in circuit and a resistance B such thatthe deflection 6 may be intermediate between 6i and 62,we have ^ cote = B+ a+x-^B (4) Subtract (2) from (4) and ^ (cot 0 - cot ) =x + B -B,... (5) From (3) and (5) x-\- B — B2 _ cot 6— cot 6, (5ot^r=^^x^; and x = + CB,^^^ -cot^.^ ^ ^cot e, — cot Example. The tangent galvanometer gave the following deflections withthe resistances indicated: Ohms. De FLECTION?;. COTAXGEXTS. Right. Left. Average. 12 « ° ° 3 61. X BESISTANCE. 31 Therefore, x- = 3 + (12 - 3) In this case B was zero. — = G 92 26. The Reflecting Gal-vanometer. — For the pur-pose of observmg a verysmall deflection of theneedle of a galvanometer,a lioiit mirror is attachedto the movable system, anda beam of light reflectedfrom this serves as a longpointer without lo a o-alvanometer of the tripod pattern is shownin Fig. 8; the mirror maybe seen at the centre of thecoil. The instrument issurmounted with a longrod, on which the curvedmagnet may slide up anddown. It is held in placeby friction. This magnet isemployed to vary the sen-sitiveness of the increase its deflectionfor a given small current,the plane of the mirror,which contains the mag-netic needle at its back inthe form of several piecesof very thin watch-spring, is first made to coincide as Fig. 8. 32 ELECTBICAL MEASUHEMENTS. nearly as possible with tlie magnetic meridian. Thenorth-seeking pole of the control magnet is then turnedtoivard the north. It must be remembered that themag
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Keywords: ., bookcentury1800, bookdecade1890, bookpublisherbosto, bookyear1895
