Aptitude Test Problems in Physics Science for Everyone by S Krotov ( PDFDrive.com )

Fig. 89

84 Aptitude Test Problems in Physics

3.30. Given two different ammeters in

which the deflections of the pointers are

proportional to current, and the scales are

uniform. The first ammeter is connected to

a resistor of resistance R, and the second to

a resistor of unknown resistance B x. At

first the ammeters are connected in series

between points A and B (as shown in

R,

-01

Fig. 88

Fig. 88). In this case, the readings of the

ammeters are tr., and 71 2. Then the ammeters

are connected in parallel between A and B

(as shown in Fig. 89) and indicate n; and

n2'

Determine the unknown resistance Rx

of the second resistor.

3.31. Two wires of the same length but of

different square cross sections are made

from the same material. The sides of the

cross sections of the first and second wires

are di = 1 mm and d 2 = 4 mm. The cur-

rent, required to fuse the first wire is / 1 -,-

10 A.