### Current Electricity

goals
A strip of copper and another germanium are cooled from room temperature to $80$K. The resistance of.
Thermoelectric series helps us to find:
For a cell the graph between the potential difference (V) across the terminals of the cells and the current (I) drawn from the cell is shown in the figure. The emf and the internal resistance of the cell are:
A rod of length $L$ and cross-section area $A$ lies along the x-axis between $x = 0$ and $x = L$. The material obeys Ohms law and its resistivity varies along the rod according to $\rho(x) = \rho_0e^{-x/L}$. The end of the rod at $x = 0$ is at a potential $V_0$ and it is zero at $x = L$
Let us consider further the use of the d Arson val meter as a current-measuring instrument, often called an ammeter. To measure the current in a circuit, an ammeter must be inserted in series in the circuit so that the current to the measured actually passes through the meter. If a galvanometer is inserted in this way, it will measure any current from zero to 1m A. However, the resistance of the coil adds to the total resistance of the circuit, with the result that the current after the galvanometer is inserted, although it is correctly indicated by the instrument, may be less than it was before insertion of the instrument. It is evidently desirable that the resistance of the instrument should be much smaller than that of the remainder of the circuit, so that when the instrument is inserted it does not change the very thing we wish to measure. An ideal ammeter would have zero resistance.