### 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[1]

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.

### Unformatted Attachment Preview

Purchase answer to see full attachment

## Final Answer

Attached.

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

[1]

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

[2]

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

1

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

[3]

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.

2

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

load.

•

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.

3

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.

https://phet.colorado.edu/sims/html/ohms-law/latest/ohms-law_en.html

https://phet.colorado.edu/sims/html/circuit-construction-kit-dc/latest/circuit-construction-kit-dc_en.html

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.

Develop your understanding:

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.…

7

Physics Lab (Online Simulation)

Demonstrate your understanding:

Directions: As you answer the questions, explain in your own words why your answer

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?

(Answer, explain, evidence)

• 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...

Brown University

1271 Tutors

California Institute of Technology

2131 Tutors

Carnegie Mellon University

982 Tutors

Columbia University

1256 Tutors

Dartmouth University

2113 Tutors

Emory University

2279 Tutors

Harvard University

599 Tutors

Massachusetts Institute of Technology

2319 Tutors

New York University

1645 Tutors

Notre Dam University

1911 Tutors

Oklahoma University

2122 Tutors

Pennsylvania State University

932 Tutors

Princeton University

1211 Tutors

Stanford University

983 Tutors

University of California

1282 Tutors

Oxford University

123 Tutors

Yale University

2325 Tutors