Bukhovtsev-et-al-Problems-in-Elementary-Physics

ELECTRICITY AND MAGNETISM 103
where e is the charge of an ion. and n and v are the concentrations
and velocities of the positive and negative ions.
Why is the amount of substance evolved. for example, on
the cathode considered to be proportional to the full current,
and not to the current en+v+?
492. What minimum change in temperature can be determined
with the aid of an iron-constantan thermocouple, if the
measuring instrument (galvanometer) has a sensitivity of 10- 9 A
and a resistance of R = 20Q? The e. m. f. of the thermocouple
is 50 microvolts (50 X 10- 8 V) per degree and its resistance
r=5Q.
493. The temperature of the hot joints of a thermoelectric
battery /1= 127°C and of the cold ones t a = 27°C. The e. m. f.
of the battery tB = 4 V. Two calories of heat are supplied to the
heated joints in a unit of time to maintain a constant temperature.
An electrolytic bath with a solution of blue vitriol is connected
to the. battery. What maximum (theoretical) amount of
copper can be deposited on the cathode in a unit of. time?
494. A current with an intensity of I flows through a storage
battery with an internal resistance of r and an e. m. f.
of