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Energy in a Circuit
Energy in a Circuit
Energy In = Energy Out
A power source, battery, cell, or capacitor all provide an electric potential in terms of Energy per charge [Joules/Coulomb]. It is considered a power source due to the measurement of how quickly it can provide this energy [Watts]
Energy into a circuit must equal energy out [Kirchhoff's 2nd Rule]. There are areas of high potential (potential energy per charge) and low potential (can be read as zero) energy per charge.
Resistors in Series or Parallel
Resistors in Series or Parallel
Open the 'LAB' ,
Instructions
Measure the actual resistance of a range of resistors using an ohmmeter as shown above, then measure the combined resistance of resistors in series and parallel.
0. Resistor Values
Determine the values of the RED, GREEN and BLUE resistors.
1. Resistors in Parallel
Combine two of the resistors in parallel and measure the combined resistance, as shown in the circuit diagram and photograph below.
Repeat for other combinations of resistors.
Calculate the reciprocals of the resistances and enter these values in the table below.
The change in voltage per branch of a parallel circuit is constant. Therefore, the relationship can be written as above. The current (I) then can cancel, resulting in the generalized equation for resistance in a parallel circuit.
Show that three resistors in parallel of 20Ω, 40Ω, and 60Ω have a combined resistance of 11Ω.
Check that your relationship also applies to three resistors in parallel.
For each of the circuits shown, given a 6-V power supply, determine the change in voltage, current, and power output for each resistor.
In all of images to the right, the resistors have the following values:
Green - 5 Ω
Blue - 10 Ω
Red - 20 Ω
Additional Resources: 5.2 Resources
2. Resistors in Series
Combine two of the resistors in series and measure the combined resistance as shown in the circuit diagram and photgraph below.
Record the readings in a table like the one below.
Repeat for other combinations of resistors. Try to avoid using resistors that vary greatly in their magnitude. Can you deduce a relationship for resistors in series?
Check that your relationship also applies to three resistors in series.
3. Mixed Series and Parallel circuits
There are 9 different circuits shown in the photos below. Calculate the combined resistance using the relationships for series and parallel circuits. Check your predictions by measuring the combined resistance with an ohmmeter.
Combine parallel resistors into series.
For circuit A:
The two resistors in parallel (each 5Ω) combine to 2.5Ω.
Add total resistors in series.
For circuit A:
Can now be treated like a series circuit. 5Ω + 2.5Ω = 7.5 Ω.
Determine the total resistance of each of the circuits shown above.
Green = 5Ω, Blue = 10Ω and Red = 20Ω
VIRP Table Usage:
VIRP Table Usage:
Given a 12V, power supply, determine the current, change in voltage and power per resistor in the circuit to the right.
It's like Sudoko, given what you have, can you fill in the missing values following four guidelines:
Convert parallel resistors into series (Equivalent resistance)
V = I x R, P =I x V
Resistors in series have the same current.
Resistors in parallel have the same change in voltage.
R_1 = 10 Ω,
R_2 = 5 Ω, R_3 = 20 Ω, R_4 = 20 Ω,
R_5 = 10 Ω
The steps I followed to solve the example above.
Place given information into the table. (G)
Determine the effective resistance of R_2, R_3 and R_4.
Calculate the total resistance of the circuit.
Determine the total current.
Total current is the same for R_1 and R_5 and R_2,3,4.
Determine changes in voltage for R_1 and R_5.
Changes in voltage for R_2,3,4
Change in voltage for parallel resistors are equal.
Current thru R_2.
Current thru R_3 and R_4.
Total power of circuit
Power of R_1
Power of R_2
Power of R_3
Power of R_4
Power of R_5
Circuit Problem Solving TSPs
Circuit Problem Solving TSPs
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