Question

2. Consider a lightbulb circuit such as the one in FIGURE Q27.1.

a. From the simple observations and measurements you can make on this circuit, can you distinguish a current composed of positive charge carriers from a current composed of negative charge carriers? If so, describe how you can tell which it is. If not, why not?

b. One model of current is the motion of discrete charged particles. Another model is that current is the flow of a continuous charged fluid. Do simple observations and measurements on this circuit provide evidence in favor of either one of these models? If so, describe how. If not, why not?

Short answer

a. No, we cannot distinguish a current composed of positive charge carriers from a current composed of negative charge carriers.

b. Yes, simple observations and measurements on this circuit provide evidence in favor of either one of these models.

Step-by-step solution

Concept Introduction (Part a)

Consider the light bulb in the circuit shown in Fig. 27.1. This observation shows the direction of the flow of current in the circuit. Observations only indicate the necessary conditions and direction of the current. The flow of electrons typically opposes the direction of the current.

However current is the result of the flow of electrons only. The physical movement is only of electrons (negative charge carriers).

Explanation (Part a)

Positive charge carriers move in an immobile manner.

In contrast to electron flow, the flow of current is the movement of positive charge carriers.

Positive charge carriers denote logical movement; negative charge carriers denote the physical movement of the same current. So current due to positive charge carriers cannot be distinguished from current due to negative charge carriers.

Final Answer (Part a)

In this instance, we cannot tell a current with positive charge carriers from one with negative charge carriers.

Concept Introduction (Part b)

Consider the light bulb in the circuit shown in Fig. 27.1. This observation shows the direction of the flow of current in the circuit. Observations only indicate the necessary conditions and direction of the current. The flow of electrons typically opposes the direction of the current.

However current is the result of the flow of electrons only. The physical movement is only of electrons (negative charge carriers).

Explanation (Part b)

Consider the simple experiment:

This observation supports the fluid model of the electricity:

1. The fluid flow occurs when pressure difference exists between two points. The electric current exists when there is potential difference between two points.

2. The fluid flows through the pipe connecting the point of high pressure to low pressure. The electric current requires the conductor to pass from one point to another.

3. Though the speed of fluid flowing through the pipe is less, the pressure is felt immediately when tap is turned on. Though the speed of electrons flowing through conductor is less, the effect of current is felt instantaneously the switch is in on position.

Final Answer (Part a)

Hence, in order to validate any of these models, it is simply necessary to observe and measure this circuit.