(^68) Aptitude Test Problems in Physics
water is c, = 4.2 J/(kg.1(), and the latent
heat of fusion of ice is A. = 340 kJ/kg.
Determine the mass mice of ice in the
bucket at the moment it is brought in the
room, neglecting the heat capacity of the
bucket.
2.37*. The properties of a nonlinear resis-
tor were investigated in a series of ex-
periments. At first, the temperature depen-
dence of the resistor was studied. As the
temperature was raised to T 1 = 100 °C,
the resistance changed jumpwise from
Rl = 50 Q to R2 = 100 Q. The reverse ab-
rupt change upon cooling took place at
T2 = 99 °C. Then a d.c. voltage U 1 =
60 V was applied to the resistor. Its temper-
ature was found to be Ts = 80 °C. Final-
ly, when a d.c. voltage U2 = 80 V was
applied to the resistor, spontaneous current
oscillations were observed in the circuit.
The air temperature To in the laboratory
was constant and equal to 20 °C. The heat
transfer from the resistor was proportional
to the temperature difference between the
resistor and the ambient, the heat capacity
of the resistor being C -= 3 J/K.
Determine the period T of current oscil-
lations and the maximum and minimum
values of the current.
2.38. When raindrops fall on a red-brick
wall after dry and hot weather, hissing
sounds are produced.
Explain the phenomenon.
2.39. A thin U-tube sealed at one end con-
sists of three bends of length 1 = 250 mm
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