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

Fundamentals of Circuits II: Currents & Circuits v 0.3
to the current in a circuit as opposed to something that uses up current. If each bulb provides
its own resistance, how is the total resistance of a circuit is affected by the addition of bulbs as
in Fig. 1(b)?
Question 1.10 Create a qualitative rule which can be used to predict whether current increases
or decreases as the total resistance of a circuit is increased.
Real-Time Physics Comment: “The rule you have formulated based on your observations
with bulbs may be qualitatively correct–correctly predicting an increase or decrease in current–
but it won’t be quantitatively correct. That is, it won’t allow you to predict the exact sizes
of the currents correctly. This is because the resistance of a bulb to current changes as the
current through the bulb changes. Another common circuit element is a resistor. A resistor
has a constant resistance to current regardless of how large the current through it. In the next
activity you will reformulate your rule using resistors.”
Prediction 1.4 Fig. 4 shows circuit diagrams where the light bulbs of Fig. 1 have been replaced
by identical resistors. Consider the amount of current going through each resistor in Figures
4(a) and 4(b)? Rank the currents through each resistor resistors A, B and C. Explain your
reasoning. (You may consider these resistors as ideal resistors: an ideal resistor has a constant
resistance independent of the current passing through it.)
To test your predictions, in addition to the equipment you have been using, you will need
• Two 10-ohm resistors
Activity 1.3: Current in a simple circuit with resistors
Step 1: Continue to use the experiment file L2A1-2 (Two Currents ).
Step 2: Zero the probes with them disconnected from the circuit.
Step 3: Connect circuit shown in Fig. 5(a).
Step 4: Withthecurrentprobes, usetheanalysisfeatureinthesoftwaretomeasurethecurrent
through resistor A in circuit 5(a) and the currents through resistors B and C in circuit
5(b).
PHYS-204:Physics II Laboratory 8