PURPOSE

To study the characteristics of voltage and current in a battery powering an ohmic (linear) circuit element and two non-ohmic (non-linear) circuit elements.

MATERIALS digital multimeter, ammeter, component box, dc power source.

RELEVANT FORMULAS
 
 
 

Ohms’ law:                                                          
 
 
 

DISCUSSION

Fig. 2.06-1 shows an ideal battery; that is, a battery with no internal resistance. This power source is connected to a circuit element of resistance R. The resistance of a circuit element is defined as:

where V is the potential drop across the circuit element, and I is the current through the circuit element. The unit of resistance, volts per ampere, is also called the ohm (Ω). If the resistance is constant for all values of I the circuit element is said to be ohmic. For an ohmic circuit element a graph of I vs. V will be a straight line through the origin (Fig. 2.06-2a) with slope of ΔI/ΔV or 1/R, which is a constant. The ideal battery in Fig. 2.06-1 produces a constant potential difference across its terminals independent of the current being delivered to the load R and has the V-I graph shown in Figure 2.06-2b.