From http://www.physicsclassroom.com/Physics-Interactives
Name:
DC Circuit Builder – Parallel Circuit
Goal: To analyze mathematical relationships between quantities for parallel circuits.
Getting Ready: Using your computer, tablet or phone and navigate to:
http://goo.gl/M4Ewmh
Tap or click the link to open the DC Circuit Builder. Once opened, select the pencil icon and use
the tools (at the bottom of the screen) to build a circuit. Simply select a bulb, resistor, wire or
ammeter (the rectangular box) and tap or click in the workspace where you wish it to be located.
You’ll get the hang of it quite quickly.
Note that the electric potential values are listed on the diagram at the corner of every square on
the grid. Current values are listed on the ammeters. To change a battery voltage or a resistor
value, select the second icon at the bottom of the screen; a magnifying glass appears above the
circuit element. Adjust the voltage or the resistance using the up/down arrows next to the digital
meter.
Build, Measure, Analyze:
Build the circuit shown with three resistors, four ammeters and a battery. Determine the values
of current (amps) and electric pressure (volts) at the indicated locations.
12 Volts V = _____
12 Volts
12 Volts V = _____
12 Volts V = _____
V = _____
1
2
3
B
6
I = ______
Amps
2
I = _____
Amps
0 Volts
V = _____
0 Volts
V = _____
0 Volts
V = _____
0
V = _____
Volts
1.
2 Amps I = _____
2 Amps
I = _____
For resistors 1, 2, and 3 and for the battery (B), calculate the electric potential difference and
fill in the table below.
B
Electric Potential
Difference (∆V)
12V
1
12V
2
12V
12V
Element
3
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Current (I)
Resistance (R)
6A
2A
-6
2A
6
2A
6
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2.
How does the electric potential difference across each resistor (∆V1, ∆V2, ∆V3) compare to
one another and to the electric potential difference across the battery (∆VB)?
All branch voltages are equal to the battery voltage
dV1 = dV2 = dV3 = dVB
3. How does the current in the battery (IB) compare to the summative current in the three
resistors (I1 + I2 + I3)?
IB is equal to the sum of the individual branch currents (I1 + I2 + I3)
IB = I1 + I2 + I3
4.
Write the above relationship as an equation:
5.
Calculate the ratio of electric potential difference to current for the battery.
∆VB/IB = ____________________
dVB / IB = 12 V / 6 A = 2 Ohms
How does this ratio compare to the resistance values of the resistor? Attempt to write an
equation relating the ∆VB/IB ratio to R1, R2, and R3 values. (This is a challenge!)
smaller ratio than any individual resistor value it represents the total resistance (Req).1 / (dVB /
IB) = 1 / R1 + 1 / R2 + 1 / R3 (or: dVB / IB = 1 / (1/R1 + 1/R2 + 1/R3))
6.
Alter the values of the battery voltage and the resistance of the resistors so that each resistor
has a different resistance. Then make measurements and complete the table.
Element
B
Electric Potential
Difference (∆V)
12V
1
7.
2
12V
12V
3
12V
Current (I)
Resistance (R)
9A
4A
--
3A
3
4
2A
6
Using values from the circuit analyzed in Question #6, identify as many mathematical
equations as you can that relate ∆V, I and R for individual circuit elements or for the circuit
as a whole. For each equation that you write, demonstrate its validity by substituting in
values from the table above.
Equation
Demonstration of Equation’s Validity
a.
I1 = dV1 / R1
b.
dVB = dV1 = dV2 = dV3
c.
2 V = 12 V = 12 V = 12 V
IB = I1 + I2 + I3
9A=4A+3A+2A
Req = dVB / IB
1.33 Ohms = 12 V / 9 A
I3 = dV3 / R3
2 A = 12 V / 6 Ohms
d.
e.
4 A = 12 V / 3 Ohms
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This document should NOT appear on other websites.