Complete Electronics Self-Teaching Guide with Projects

The Graph of Resistance

21 The voltage drop across a resistor and the current flowing through it can be plotted on a simple graph. This graph is called a V-I curve.

Consider a simple circuit in which a battery is connected across a 1 kΩ resistor.

Questions

A. Find the current flowing if a 10-volt battery is used. __________

B. Find the current when a 1-volt battery is used. __________

C. Now find the current when a 20-volt battery is used. __________

Answers

A. 10 mA

B. 1 mA

C. 20 mA

22 Plot the points of battery voltage and current flow from problem 21 on the graph shown in Figure 1.5, and connect them together.

Figure 1.5

Question

What would the slope of this line be equal to? _____

Answers

You should have drawn a straight line, as in the graph shown in Figure 1.6.

Figure 1.6

Sometimes you need to calculate the slope of the line on a graph. To do this, pick two points and call them A and B.

• For point A, let V = 5 volts and I = 5 mA
• For point B, let V = 20 volts and I = 20 mA

The slope can be calculated with the following formula:

In other words, the slope of the line is equal to the resistance.

Later, you learn about V-I curves for other components. ...