Electrical measurementsA laboratory manual . ater than the of the standard cell. Example. To determine the Consta?it of a Thomson Graded Galvanometer {ammeter) without its Field-Magnet. AX B Formnla: I = Base number where A is the constant to be determined, I) the deflection, andby base number is meant the number indicating the position ofthe sliding magnetometer box on the base of the instrument. Data : i^i = 2110 ; R2 = 1254; and r = 10 ohms at 24° C. of standard cell at ^ C. = volts. Therefore, I =^ . 2110 + 1254 ^ ,^29 2110 ^ JD := divisions. Base num
Electrical measurementsA laboratory manual . ater than the of the standard cell. Example. To determine the Consta?it of a Thomson Graded Galvanometer {ammeter) without its Field-Magnet. AX B Formnla: I = Base number where A is the constant to be determined, I) the deflection, andby base number is meant the number indicating the position ofthe sliding magnetometer box on the base of the instrument. Data : i^i = 2110 ; R2 = 1254; and r = 10 ohms at 24° C. of standard cell at ^ C. = volts. Therefore, I =^ . 2110 + 1254 ^ ,^29 2110 ^ JD := divisions. Base number = 32. Hence from the above formula, ^^0-229 X 32 ^ 172 ELECTRICAL MEASUREMENTS. This constant is the value of the magnetic field at the needlewhen no current is flowins:. 83. Second Method by Means of a Standard Cell.— This method, the connections for which are shown inthe diagram (Fig. 83), admits of using a resistance rof such dimensions that the difference of potentialbetween its terminals may be greater or less than the. Fig. 83. of the standard cell or cells employed. Theresistance must be capable of carrying the current duringthe time required to effect the balance without apprecia-ble heating; or, better, it may be immersed in oil, with astirrer, so that its tem})erature may be known. Set up two 10,000 ohm resistance boxes in series witha battery B^ of higher than the standard cellor the between A and B. From the terminals ofit form a shunt circuit containing a sensitive high resist-ance galvanometer and a standard cell. It is better also MEASUBEMENT OF CUB BENT, 173 to include a high resistance HR in this circuit. Thepoles of the standard cell must be turned in such direc-tion that the between the terminals of M opposesthe of the cell. Then, keeping a total of 10,000ohms in the tivo boxes R and R^ vary the part containedin each box till, on closing the key, the galvanometer G-shows no deflection. The between the termi
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