Description

PHYS 2020 Lecture 14 (Laboratory)

Kirchoff’s Laws

Adapted from the University of Sharjah

We did a walkthrough of some problems involving more complex circuits, but it’s a good idea to

reinforce the concept.

Materials (see Appendix):

•

None

Activity 1: Kirchoff’s Current Rule

Since we have limited lab equipment in an online situation, we will be exploring the concepts virtually

using a PhET simulation. Click on the following link to use today’s simulation.

1- Use the DC Power supply, the resistors and the connecting wires provided on the simulation

software to build up the circuit below (if you can’t get the specific values of the resistors, don’t

panic). Confirm you have conventional current turned on.

R1

R2

1

2

R3

2- Change the power supply outputs and the resistor values and observe how the currents change in

response

Think About It:

Can you get a current to go backwards through a battery? What does it take?

3- Connect Ammeters in series with each resistor (as shown below, assume all current directions follow

the loops) to measure the current flowing through each resistor record your values in the table. Note

that your resistors, emfs and currents will be different that shown in the image.

4- Calculate the expected currents for the voltages and resistors of your circuits. Include your work as

an appendix to your report, and compare your results to the simulated values (including an error

assessment assuming the simulated value is correct).

I1

I2

I3

Loop 2

Loop 1

1

2

1 = ………………….

2 = …………………

Experimental results

R (k)

Calculated results

I (mA)

R (k)

Think About It:

Is Kirchhoff’s current law satisfied? How can you tell?

I (mA)

Activity 2: Kirchoff’s Loop Rule

1- Reset the resistors and voltages to new values

2- Connect voltmeters in parallel with each resistor (as shown below for resistor 1) to measure the

voltage drop across it; fill your data for the voltages in the table.

IV1

Think About It:

What happens if you swap the leads from the voltmeter across the resistor? Would it make a

difference in your results?

1 = ………………….

2 = …………………

Experimental results

R (k)

Calculated results

V (V)

R (k)

Think About It:

Is Kirchhoff’s voltage law satisfied? How can you tell?

V (V)

3- Calculate the expected currents for the voltages and resistors of your circuits. Include your work as

an appendix to your report, and compare your results to the simulated values (including an error

assessment assuming the simulated value is correct).

Activity 3: Extra Practice

1- For extra practice on Kirchhoff’s laws, connect the circuit below and do current and voltage

measurements using the ammeter and the voltmeter. Show your findings on the table below.

Experimental results

R (k)

I (mA)

Calculated results

V (volt)

R (k)

1

1

1

1

0.1

0.1

I (mA)

V (volt)

2- Calculate the expected currents for the voltages and resistors of your circuits. Include your work as

an appendix to your report, and compare your results to the simulated values (including an error

assessment assuming the simulated value is correct).

Deliverables

We need an informal report describing what you did and what you learned. Imagine you are talking to

your parents or your boss, and describing the activities you just completed. Make sure to include any

pictures and resulting understanding you have gained. Submit a copy of this report for grading.

Rubric:

Documentation

Missing

25 (0.00%)

Novice

15 (30.00%)

Partial

20 (40.00%)

Proficient

25 (50.00%)

Did not submit

Narrative unclear,

incomplete thoughts

and/or sentences. Did

not include sufficient

information for a person

to replicate the work

Narrative was fairly clear,

but left out something

significant (i.e, meaning

of the results, numbers

without units or

uncertainties)

Ideas were expressed in a

clear and organized

fashion. It was easy to

figure out what was going

on, and how to repeat

the experiment if desired.

Included discussion of

results compared to

accepted values (with

appropriate uncertainties

and units)

A post-lab quiz will also be required to assess your understanding of the goals for this lab, and will count

for half the grade.

Question 1 (1 point)

Which is a correct statement of Kirchhoff’s Loop Law?

a

The sum of currents around any closed loop is zero

The sum of voltages around any closed loop is zero

The total current going into a junction is equal to the total current coming out of

the junction

The total voltage going into a junction is equal to the total voltage coming out of

it

Which is a correct statement of Kirchhoff’s Junction Law?

The sum of currents around any closed loop is zero

The sum of voltages around any closed loop is zero

The total current going into a junction is equal to the total current coming out of

the junction

The total voltage going into a junction is equal to the total voltage coming out of

it

What would be the correct junction law equation for the junction shown below?

13

“T

12

13 = 11 + 12

11 + 13 = 12

11 = 12 + 13

=

11 + 12 + 13 = 0

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