Pre-LAB 4 Assignment Fundamentals of Circuits II: Currents ...

Fundamentals of Circuits II: Currents & Circuits v 0.3
Objectives
• To understand current in a circuit where a battery lights a bulb.
• To understand series connections in an electric circuit.
• To understand the relationship between the current in all parts of a series circuit.
• To understand the meaning of parallel connections in an electric circuit.
• To understand the relationship between the currents in all parts of a parallel circuit.
• To begin to understand the concept of resistance.
Overview
In the previous lab you found that a bulb only lights when there is an electric current passing
through the bulb. You also found that the bulb must be connected to a battery in a complete,
continuous circuit in order for there to be a current. Specifically, there must be a continuous
connection from the positive terminal of the battery, through the connecting wire to the bulb,
through the bulb, through the connecting wire to the negative terminal of the battery and
through the battery.
Recall that you measured the current both as it entered current elements like a battery or
a bulb and when it left. From these measurements you discovered that the electric current
flowing out of a device is equal to the current flowing into it. These devices did not seem to
“use up” any current which passed through. Current it seems doesn’t just disappear. This
suggests that electrical current is the flow of some conserved quantity i.e., electric charge. In
addition, by measuring voltage in circuits with one bulb and with two bulbs you observed that
the potential difference (voltage) across a battery (if one can neglect its internal resistance) is
fairly constant whether it is connected to one light bulb or two. In other words, the voltage of
a battery is a property of the battery and not of the circuit.
By contrast, you found that adding a second bulb in series to the first lead to a decrease in
the current. Circuit elements like bulbs provide a resistance to electrical currents. The total
resistance of a circuit determines the current when the circuit is connected to a battery. The
larger the resistance, the smaller the current.
In this lab we will consider more complicated circuits in order to extend and reinforce what
we have learned previously. You will be comparing currents at different points in these circuits
by making measurements using current probes and by comparing the brightness of bulbs. This
lab has been adapted from the Real Time Physics Active Learning Laboratories [?]. The goals,
guiding principles and procedures of this labs closely parallel the implementation found in the
work of those authors [?, ?, ?].
Investigation 1:
Current in Series Circuits
In the spirit of scientific discovery, you will make a series of predictions about currents in
various circuits. Afterwords, you will compare these predictions with measurements and observations.
If you find that your experimental measurements and/or observations disagree with
your predictions you should identify which if any of the assumptions which lead you to your
PHYS-204:Physics II Laboratory 2