 Science
Unit 3 Ohm's Law Kirchoffs Law Electricity and Light Lab Report

### Question Description

This is an online lab with online simulations and questions related to those simulations.

Theory:

A D.C. circuit consists of sources of direct current (EMFs), connected to a network of elements.If the elements are ohmic (obey Ohm’s Law) then the currents through the elements are directly proportional to the voltages applied across the elements.For ohmic elements, the relation between the current through an element (I), in amps, and the voltage across the element (V), in volts, is

V = IR

where R is the resistance of the element in ohms.Resistors, which are commonly used in electronic devices, are ohmic.

The lab is attached to this and you only need to complete what is in the file itself. There is no need for lab report or anything.

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Physics Lab (Online Simulation)
OHM’S LAW - KIRCHOFF’S LAW
Electricity and Light
Unit 3
TA name:

Due Date:

Student Name:
Student ID:

Theory:
A D.C. circuit consists of sources of direct current (EMFs), connected to a network of
elements. If the elements are ohmic (obey Ohm’s Law) then the currents through the
elements are directly proportional to the voltages applied across the elements. For ohmic
elements, the relation between the current through an element (I), in amps, and the
voltage across the element (V), in volts, is
V = IR



Where R is the resistance of the element in ohms Resistors, which are commonly used in
electronic devices, are ohmic.
If two or more resistors are connected in series with a voltage source, as illustrated in
Figure 18-1, they collectively behave as an equivalent single resistor with resistance, Rser,
where
Rser = R1 + R2 + R3 +  + Rn

R1

R3

R2



Rn

V

Figure 18-1
the resistors are connected in parallel to the voltage source, as illustrated in Figure 18-2, then
they collectively behave as an equivalent single resistor with a resistance, Rpar, where

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Physics Lab (Online Simulation)

V

R1

R2

R3

Rn

Figure 18-2

1
1
1
1
1
=
+
+
++
R par R 1 R 2 R 3
Rn



The circuits illustrated in Figures 18-1 and 18-2 can be reduced to a single loop
containing a single voltage source and a single resistor. And Ohms Law can be used to
determine the currents in the circuit.
If however the circuit contains more than one voltage source in a network of resistors, the circuit usually
cannot be reduced to a single loop. Kirchhoff’s rules are useful in analyzing a multi-loop circuit.

This Prelab is worth 15 points
(1) Write down an equation and solve for the total resistance of three resistors R1=100Ω,
R2=150 Ω, R3=350Ω in the resistors were arranged in the following combination:
a) All three in series
(1 point)

𝑅𝑡𝑜𝑡𝑎𝑙 = 𝑅1 + 𝑅2 + 𝑅3
𝑅𝑡𝑜𝑡𝑎𝑙 = 100+ 150 +350=600 Ω

b) All three in parallel (1 point)

1
𝑅𝑡𝑜𝑡𝑎𝑙
1
𝑅𝑡𝑜𝑡𝑎𝑙

1

1

1

=𝑅 +𝑅 +𝑅
1

1

2

3

1

1

41

= 100 + 150 + 350 = 2100

𝑅𝑡𝑜𝑡𝑎𝑙 = 51.22Ω

c) How would you arrange these three resistors to get a net resistance of 410 Ω? (1 point)
• I would connect R1 and R2 in parallel. Then connect this combination in series with R3.
The terminal resistance of this circuit would be 410Ω.

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Physics Lab (Online Simulation)

(2) If you have an experimental setup which has three unknowns, how many linearly
independent equations do you need to determine the unknowns to find one unique
solution? (1 point)
• Three linearly independent equations.
(3) What is Kirchhoff’s law of current? What does it conserve? (1 point)
• It states that for a parallel path the total current entering a circuit junction is exactly equal
to the total current leaving the same junction.
• It conserves charge entering or leaving a junction.
(4) What is Kirchhoff’s law of voltage? What does it conserve? (1 point)
• It states that for a closed loop series path the algebraic sum of all the voltages around any
closed loop in a circuit is equal to zero.
• It involves conservation of energy around a closed circuit path.

(5) Electrical circuits have two main problems: “Short” and “Open”. Define these two
conditions with diagram and an example showing the consequence of each of these faults.
(Use back of the page if necessary). (2+2 = 4 points)
• Short circuit condition is a fault in which there is low resistance amid two
conductors supplying electrical power to a circuit i.e. a conductor bypasses the

Open circuit is a condition whereby, two terminals of a circuit are disconnected
externally and resistance at this point is infinite hence no current flow. Another
possible occurrence is an open switch in the circuit.

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Physics Lab (Online Simulation)

.

R1

I2

I1

R2

R3

V1

Loop 1
I1

V2

Loop 2
I3

I2

(6) Apply Kirchhoff’s law of current and voltage in loop 1 and loop 2 of the above circuit
and write down the corresponding equation. (2.5 + 2.5 = 5 points)
Loop 1:
Current equation:
𝑰𝟏 + 𝑰𝟐 = 𝑰𝟑
Voltage equation:

−𝑽𝟏 + 𝑰𝟏 𝑹𝟏 + 𝑰𝟑 𝑹𝟑 = 0

Loop 2:
Current equation:
𝑰𝟏 + 𝑰𝟐 = 𝑰𝟑
Voltage equation:
−𝑽𝟐 + 𝑰𝟐 𝑹𝟐 + 𝑰𝟑 𝑹𝟑 = 0

4

Physics Lab (Online Simulation)

Part A: Ohm’s Law
This lab uses the Ohm’s Law and Circuit Construction Kit DC simulation from PhET
Interactive Simulations at University of Colorado Boulder, under the CC-BY 4.0 license.

Learning Goals
1. As you change the value of the battery voltage, how does this change the current through
the circuit and the resistance of the resistor? If the current or resistance remains constant,
why do you think?
• Increasing voltage increases the current and voltage drops across the resistor. The
resistance remains constant; this is because the value of resistance is dependent on
the material of the resistor and not on the voltage connected across it. At constant
resistance, the current is directly proportional to voltage.
2. As you change the value of the resistance of the resistor, how does this change the current
through the circuit and the battery voltage? If the current or voltage remains constant,
why do you think?
• Voltage remains the same but current increases when the resistance is reduced.
This is because voltage depends on the battery voltage which is independent of
the resistance. Resistance limits current and is indirectly proportional to current as
stated in Ohm’s law.
3. Use understanding to make predictions about a circuit with lights and batteries.
• In a circuit, lights act like resistors.
• Increasing the lights in series (increases resistance) decreases current hence
making the lights dimmer at constant voltage.
• Increasing the number of batteries (increases voltage) with constant number of
lights increases current flowing in the circuit hence making the lights brighter.
1. Open Ohm’s Law, and then explore to develop your own ideas about how resistance,
current, and battery voltage are related.

5

Physics Lab (Online Simulation)

Describe several of your experiments and your observation with captured images from the
simulation.

a. At constant resistance, increasing voltage increases the current flowing in the
circuit.

b. At constant resistance, decreasing voltage decreases the current in the circuit.

6

Physics Lab (Online Simulation)

c. At constant voltage, increasing resistance decreases current.

d. At constant voltage, decreasing resistance increases current.…

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Physics Lab (Online Simulation)

makes sense and provide evidence from your #1 experiment. Add more experiments to #1
if you need to get better evidence.
2. If you change the value of the battery voltage:
a. How does the current through the circuit change? (answer, explain, evidence)
• Increasing voltage increases the current
• At constant resistance, the current is directly proportional to voltage
• From Ohm’s law; V=IR

b. How does the resistance of the resistor change? (answer, explain, evidence)
• The resistance remains constant;
• This is because the value of resistance is dependent on the material of the
resistor and not on the voltage connected across it.
𝜌𝑙
• 𝑅= 𝐴
• 𝑤ℎ𝑒𝑟𝑒 𝜌 𝑖𝑠 𝑟𝑒𝑠𝑖𝑠𝑡𝑖𝑣𝑖𝑡𝑦 𝑜𝑓 𝑡ℎ𝑒 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙, 𝑙 𝑖𝑠 𝑡ℎ𝑒 𝑙𝑒𝑛𝑔𝑡ℎ 𝑜𝑓 𝑡ℎ𝑒 𝑟𝑒𝑠𝑖𝑠𝑡𝑜𝑟 𝑎𝑛𝑑 𝐴 𝑖𝑠
𝑡ℎ𝑒 𝑐𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑡ℎ𝑒 𝑟𝑒𝑠𝑖𝑠𝑡𝑜𝑟. 𝐴𝑙𝑙 𝑡ℎ𝑒𝑠𝑒 𝑎𝑟𝑒 𝑖𝑛𝑑𝑒𝑝𝑒𝑛𝑑𝑒𝑛𝑡 𝑜𝑓 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑎𝑛𝑑
𝑣𝑜𝑙𝑡𝑎𝑔𝑒.
3. If you change the resistance of the resistor:
a. How does the current through the circuit change? (answer, explain, evidence)
• Current increases when the resistance is reduced.
• Resistance limits current and is indirectly proportional to current as stated
in Ohm’s law
• From Ohm’s law; V=IR
b. How does the voltage of the battery change? (answer, explain, evidence)
• Voltage remains the same when resistance is reduced.
• This is because voltage depends on the battery voltage which is
independent of the resistance.

4. Consider the two circuits below.

8

Physics Lab (Online Simulation)

Use your understanding of voltage, resistance, and current to answer these questions:
a. What do you think will happen when the switches are closed?
• The bulbs in the second circuit will be brighter than those in the first
circuit.
• The number of bulbs in equal in both circuits (equal resistance). The
second circuit has a higher voltage source which is twice the first circuit.
Hence there is a higher amount of current flowing in the second circuit
making the bulbs brighter.
• From Ohm’s law; V=IR

b. How do you think the lights’ brightness will compare?
• The bulbs in the second circuit will be brighter than those in the first
circuit.

c. Open the Intro screen of Circuit Construction Kit DC. Build 2 circuits. Turn on
“values”. An ammeter is used to measure current in a circuit. Use the ammeter to
compare the current in the two circuits. Compare and contrast the two circuits.
Explain the difference in brightness from the two circuits by relating it to Ohm’s
Law.

The bulbs in the second circuit are brighter than those in the first circuit.
The number of bulbs in equal in both circuits (equal resistance, 20 Ohms).
The second circuit has a higher voltage source (18V) which is twice the
first circuit (9V). Hence there is a higher amount of current flowing in the
second circuit (0.9A) making the bulbs brighter.
From Ohm’s law; V=IR

9

Physics Lab (Online Simulation)

Insert a capture of the circuits with the switch closed for supporting evidence.

5. Consider the two circuits below.

Use your understanding of voltage, re... Drval (24779)
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