Even more amazing is that they do not always keep moving forward like soldiers in a parade. There are so many charged particles moving, even in small currents, that individual charges are not noticed, just as individual water molecules are not noticed in water flow. An electric field is needed to supply energy to move the charges. Unlike static electricity, where a conductor in equilibrium cannot have an electric field in it, conductors carrying a current have an electric field and are not in static equilibrium. It is important to realize that there is an electric field in conductors responsible for producing the current, as illustrated in Figure 20.4. Franklin, in fact, was totally unaware of the small-scale structure of electricity. He named the type of charge associated with electrons negative, long before they were known to carry current in so many situations. The fact that conventional current is taken to be in the direction that positive charge would flow can be traced back to American politician and scientist Benjamin Franklin in the 1700s. Figure 20.4 illustrates the movement of charged particles that compose a current.
CURRENT PHYSICS CALCULATOR GENERATOR
A Van de Graaff generator used for nuclear research can produce a current of pure positive charges, such as protons. In ionic solutions, such as salt water, both positive and negative charges move. In metal wires, for example, current is carried by electrons-that is, negative charges move. Depending on the situation, positive charges, negative charges, or both may move. The direction of conventional current is the direction that positive charge would flow. Note that the direction of current flow in Figure 20.3 is from positive to negative. The schematic represents a wide variety of similar circuits. (b) In this schematic, the battery is represented by the two parallel red lines, conducting wires are shown as straight lines, and the zigzag represents the load. A closed path for current to flow through is supplied by conducting wires connecting a load to the terminals of a battery.
We need to understand a few schematics to apply the concepts and analysis to many more situations.įigure 20.3 (a) A simple electric circuit. Such schematics are useful because the analysis is the same for a wide variety of situations. The schematic in Figure 20.3 (b), for example, can represent anything from a truck battery connected to a headlight lighting the street in front of the truck to a small battery connected to a penlight lighting a keyhole in a door. A single schematic can represent a wide variety of situations. Schematics are very useful in visualizing the main features of a circuit. Remember, calculators do not have moving parts in the same way that a truck engine has with cylinders and pistons, so the technology requires smaller currents.įigure 20.3 shows a simple circuit and the standard schematic representation of a battery, conducting path, and load (a resistor).
Such small current and energy demands allow handheld calculators to operate from solar cells or to get many hours of use out of small batteries. So why can we operate our calculators only seconds after turning them on? It’s because calculators require very little energy. The small current used by the hand-held calculator takes a much longer time to move a smaller charge than the large current of the truck starter.