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Briefing Document: ⚙️EJS Direct Current Motor 3D Model

1. Overview

This document reviews the "EJS Direct Current Motor 3D Model" resource, which is part of the Open Educational Resources / Open Source Physics @ Singapore initiative. The resource provides an interactive 3D simulation of a direct current (DC) motor, designed for educational purposes, particularly for secondary and junior college levels. The primary aim is to illustrate the principles of electromagnetic induction and how they are used to create motion in a DC motor. The resource emphasizes both the physical components of the motor as well as the underlying physics principles.

2. Core Concepts & Functionality

• Electromagnetic Induction: The fundamental principle of DC motor operation is that "electric motors turn electricity into motion by exploiting electromagnetic induction." This concept is central to the simulation and is consistently highlighted. The resource explains that a current-carrying loop in a magnetic field experiences a turning force.
• Motor Components: The simulation showcases the essential parts of a DC motor:
• Stator: The external, stationary magnet that provides a constant magnetic field.
• Armature (Rotor/Coil): The rotating coil of wire, which is an electromagnet when current passes through it.
• Split-Ring Commutator: A crucial device that reverses the current direction in the coil every half-cycle, ensuring continuous rotation.
• Carbon Brushes: Components that maintain electrical contact with the commutator as it rotates.
• Force and Torque:The armature, when carrying current, becomes an electromagnet, creating its own magnetic field.
• The interaction between the magnetic field of the stator and the armature’s magnetic field results in a magnetic force on the armature. This force is depicted by green arrows in the simulation.
• The force causes a torque (turning force) on the armature which can be calculated by “T = FmagADcosθ" where Fmag is the magnetic force, AD is the length of the coil loop and θ is the angle of the loop in reference to a reference point.
• "The coil loop rotates in an clockwise manner (view from battery side) starting 90o until it reaches the θ = 170o position (assuming that split ring angle are default at β2 = 80o)."
• Split-Ring Commutator Functionality The most important part of the DC motor is the split ring commutator. This reverses the direction of the current in the loop for every half a cycle. "A swing back and fro motion (maybe θ = 90o increase to 270o and decrease back to 90o) is all you would get out of this motor if it weren't for the split-ring commutator"
• Current Flow Visualization: The simulation allows users to visualize the direction of current flow (conventional current vs. electron flow). Users can use a checkbox to switch between the two visualizations. The direction of force can be determined by the Left Hand Rule.
• Interactive Controls: Users can control:
• The current (I) using a slider, observing the effects of reversed current.
• Play and Pause the 3D view for detailed inspection and force analysis.
• Motor vs. Generator: The resource explains that "A electric motor is a device for transforming electrical energy into mechanical energy; an electric generator does the reverse, using mechanical energy to generate electricity." It notes that the same device can be used as either a motor or generator. When a coil rotates in a magnetic field it can generate electricity: "ε = -NBA d(cos(wt))/dt = wNBA sin(wt) = εo sin(wt)"
• AC and DC Generation: The document explains the difference between AC and DC electricity generation, highlighting how the split-ring commutator is used in DC generation to "ensure the polarity of the voltage is always the same." It also details an alternative generation method of moving magnets instead of coils. "Rather than using a spinning coil in a constant magnetic field, another way to utilize electromagnetic induction is to keep the coil stationary and to spin permanent magnets (providing the magnetic field and flux) around the coil."

3. Educational Applications & Features

• Target Audience: Primarily aimed at secondary and junior college students studying physics, specifically electromagnetic induction and motor operation.
• Learning Objectives:Understand how current-carrying coils in a magnetic field experience a turning effect.
• Explain the function of a split-ring commutator.
• Describe how this turning effect results in continuous rotation in a motor.
• Discuss the relationship between motors and generators.
• Interactive Elements: The simulation allows for active, inquiry-based learning. Students can change variables and see the results directly. This makes "virtual lab" experimentation possible.
• Teacher Support: The resource links to worksheets and source codes, aiding educators in integrating the simulation into their lesson plans. There are also exercises provided for students to work through using the simulation to test hypotheses and understand physics principles.
• Advanced Learner Opportunities: The simulation is presented as remixable by advanced learners by changing parts of the source code and even sharing it through other online educational platforms.
• O Level Syllabus Alignment: The resource is explicitly linked to specific learning outcomes in the O Level syllabus, including:
• "explain how a current-carrying coil in a magnetic field experiences a turning effect"
• "discuss how this turning effect is used in the action of an electric motor"
• "describe the action of a split-ring commutator"
• Video Support: It includes a link to a video where physicists explain how to construct a simple DC motor.

4. Key Quotes & Supporting Ideas

• "Electric motors turn electricity into motion by exploiting electromagnetic induction."
• "A simple direct current (DC) motor is illustrated here. ABCD is mounted on an axle PQ."
• "The key to producing motion is positioning the electromagnet within the magnetic field of the permanent magnet..."
• "The purpose of the commutator is to reverses the direction of the current in the loop ABCD for every half a cycle."
• "A electric motor is a device for transforming electrical energy into mechanical energy; an electric generator does the reverse, using mechanical energy to generate electricity."

5. Software & Credits

• The resource requires Java to run.
• The simulation was developed by Fu-Kwun Hwang and Loo Kang Wee.

6. Additional Resources The document provides a list of additional resources and articles on DC motors and related concepts from several different sources.

7. Conclusion

The EJS Direct Current Motor 3D Model is a valuable educational resource, providing a dynamic and interactive way to understand the operation of DC motors. Its strength lies in its ability to visualize abstract concepts like electromagnetic induction, force, and torque, making them more tangible for students. The resource is well-supported with teacher materials, exercises, and links to additional learning tools. It can be used to understand how both AC and DC electricity is generated. The combination of interactive simulation, clear explanations, and syllabus alignment makes it a useful tool for physics education.

 

Direct Current Electrical Motor Model

Electric motors turn electricity into motion by exploiting electromagnetic induction. A current-carrying loop that is placed in a magnetic field experiences a turning effect.A simple direct current (DC) motor is illustrated here. ABCD is mounted on an axle PQ. The ends of the wire are connected to a split ring commutator at position X & Y. The commutator rotates with the loop. Two carbon brushes are made to press lightly against the commutators. 
The motor features a external magnet (called the stator because it’s fixed in place) and an turning coil of wire called an armature ( rotor or coil, because it rotates). The armature, carrying current provided by the battery, is an electromagnet, because a current-carrying wire generates a magnetic field; invisible magnetic field lines are circulating all around the wire of the armature.
The key to producing motion is positioning the electromagnet within the magnetic field of the permanent magnet (its field runs from its north to south poles). The armature experiences a force described by the left hand rule. This interplay of magnetic fields and moving charged particles (the electrons in the current) results in the magnetic force (depicted by the green arrows) that makes the armature spin because of the torque. Use the slider current I to see what happens when the flow of current is reversed. The checkbox current flow & electron flow alows different visualization since I = d(Q)/dt and Q= number of charge*e. The Play & Pause button allows freezing the 3D view for visualizing these forces, for checking for consistency with the left hand rule .

Description:

the following case describe a postive current i, postive B field, θ start = 90^o , split-ring commutator gap β₂= 80^o
The split-ring commutator allows electricity flows from the positive terminal of the battery through the circuit, passes through a copper brush [rectangle black boxes] to the commutator, then to the armature. 
Postive current runs through ABCD as shown in the diagram (select the checkbox labels?), a +y direction force would act on AB. An -y direction force would act on CD. Taking moments about the axle conveniently, reveals a resultant torque T = Fmag*AD*cosθ acts on the coil loop. The coil loop rotates in an clockwise manner (view from battery side) starting 90o until it reaches the θ = 170^o position (assuming that split ring angle are default at β2 = 80^o). At this θ = 170+^o position, the current is cut off. However, the momentum of the loop carries it past the horizontal position until the coil loop reaches θ = 190o position. Contact between loop and split ring commutator is established again and the current in the coil loop is now reversed (note that current i is still positive). A -y direction force now acts on AB while a +y direction force acts on CD. The rotation motion is reinforced clockwise (view from battery side) as θ continues to rotate from 190^o to 350^o. At this θ = 350+^o position, the current is cut off. However, the momentum of the loop carries it past the verticall position until the coil loop reaches θ = 10^o position. Contact between loop and split ring commutator is established again and the current in the coil loop is now reversed back to same as at θ = 90^o. A a +y direction force would act on AB. An -y direction force would act on CD and the loop reaches θ = 90^o . The cycle repeats after θ = 90^o allowing the armature to experience torque in the reinforced direction at the right time to keep it spinning. 

Function of split-ring commutator:

The purpose of the commutator is to reverses the direction of the current in the loop ABCD for every half a cycle. 
A swing back and fro motion (maybe θ = 90^o increase to 270^o and decrease back to 90^o) is all you would get out of this motor if it weren't for the split-ring commutator — the circular metal device split into parts (shown here in teal with a gap of β₂) that connects the armature to the circuit.

 

In other words

A electric motor is a device for transforming electrical energy into mechanical energy; an electric generator does the reverse, using mechanical energy to generate electricity. At the heart of both motors and generators is a wire coil in a magnetic field. In fact, the same device can be used as a motor or a generator.

When the device is used as a motor, a current is passed through the coil. The interaction of the magnetic field with the current causes the coil to spin. To use the device as a generator, the coil is spun, inducing a current in the coil.

Let's say we spin a coil of N turns and area A at a constant rate in a uniform magnetic field B. By Faraday's law, the induced emf is given by:

ε = -N d(BA cos(Φ))/dt

B and A are constants, and if the angular speed w of the loop is constant the angle is:
θ = wt

The induced emf is then:

ε = -NBA d(cos(wt))/dt = wNBA sin(wt) = εo sin(wt)

Spinning a loop in a magnetic field at a constant rate is an easy way to generate sinusoidally oscillating voltage...in other words, to generate AC electricity. The amplitude of the voltage is:
εo = wNBA

In North America, AC electricity from a wall socket has a frequency of 60 Hz. but in Singapore is 50 Hz The angular frequency of coils or magnets where the electricity is generated is therefore 60 Hz in USA or 50 Hz in Singapore.

To generate DC electricity, use the same kind of split-ring commutator used in a DC motor to ensure the polarity of the voltage is always the same. In a very simple DC generator with a single rotating loop, the voltage level would constantly fluctuate. The voltage from many loops (out of synch with each other) is usually added together to obtain a relatively steady voltage.

Rather than using a spinning coil in a constant magnetic field, another way to utilize electromagnetic induction is to keep the coil stationary and to spin permanent magnets (providing the magnetic field and flux) around the coil. A good example of this is the way power is generated, such as at a hydro-electric power plant. The energy of falling water is used to spin permanent magnets around a fixed loop, producing AC power.

 

Direct Current Motor Study Guide

Quiz

1. What is the primary function of a direct current (DC) motor? A DC motor transforms electrical energy into mechanical energy, specifically rotational motion, by leveraging the principles of electromagnetism. It uses the interaction between magnetic fields and electric currents to generate torque.
2. Explain the role of the armature in a DC motor. The armature is the rotating coil of wire within the motor that carries the electrical current, making it an electromagnet. This electromagnet interacts with the external magnetic field to produce a force and a torque, which causes the armature to spin.
3. What is a stator and its function in a DC motor? The stator is the stationary component of the DC motor, typically a permanent magnet. Its purpose is to provide a constant magnetic field that interacts with the magnetic field generated by the current in the armature to create motion.
4. Describe how the magnetic field generated by the armature interacts with the external magnetic field. The armature's magnetic field interacts with the external magnetic field of the stator, resulting in a magnetic force on the current-carrying wires of the armature. This force, described by the left-hand rule, produces torque, which causes the armature to rotate.
5. What is the function of the split-ring commutator in a DC motor? The split-ring commutator is a mechanical switch that reverses the current's direction in the armature coil every half rotation. This reversal is necessary to maintain continuous rotation of the motor in a single direction.
6. How does the split-ring commutator ensure continuous rotation of the motor? By reversing the current direction in the armature coil every half-cycle, the commutator ensures that the force acting on the armature continues to produce a torque in the same direction, allowing the motor to rotate continuously rather than oscillating back and forth.
7. Explain the concept of torque in relation to the operation of a DC motor. Torque is a rotational force that causes the armature to spin. It results from the magnetic force acting on the current-carrying wires in the armature coil. The torque is maximized when the armature is perpendicular to the magnetic field.
8. What is electromagnetic induction? Electromagnetic induction is the process by which a changing magnetic field creates an electric current. In a motor, this principle is reversed as current moving through the magnetic field creates a force and therefore motion.
9. What is the difference between the DC generator and a DC motor? A DC motor transforms electrical energy into mechanical motion while a DC generator converts mechanical energy into electrical energy. Both devices work based on the principles of electromagnetic induction and using similar components.
10. How is AC electricity generated in a simple generator? AC electricity is generated by rotating a coil within a magnetic field. This motion induces a current in the coil. With a single coil, this produces a sinusoidally oscillating voltage, the hallmark of alternating current.

Quiz Answer Key

1. A DC motor transforms electrical energy into mechanical energy, specifically rotational motion, by leveraging the principles of electromagnetism. It uses the interaction between magnetic fields and electric currents to generate torque.
2. The armature is the rotating coil of wire within the motor that carries the electrical current, making it an electromagnet. This electromagnet interacts with the external magnetic field to produce a force and a torque, which causes the armature to spin.
3. The stator is the stationary component of the DC motor, typically a permanent magnet. Its purpose is to provide a constant magnetic field that interacts with the magnetic field generated by the current in the armature to create motion.
4. The armature's magnetic field interacts with the external magnetic field of the stator, resulting in a magnetic force on the current-carrying wires of the armature. This force, described by the left-hand rule, produces torque, which causes the armature to rotate.
5. The split-ring commutator is a mechanical switch that reverses the current's direction in the armature coil every half rotation. This reversal is necessary to maintain continuous rotation of the motor in a single direction.
6. By reversing the current direction in the armature coil every half-cycle, the commutator ensures that the force acting on the armature continues to produce a torque in the same direction, allowing the motor to rotate continuously rather than oscillating back and forth.
7. Torque is a rotational force that causes the armature to spin. It results from the magnetic force acting on the current-carrying wires in the armature coil. The torque is maximized when the armature is perpendicular to the magnetic field.
8. Electromagnetic induction is the process by which a changing magnetic field creates an electric current. In a motor, this principle is reversed as current moving through the magnetic field creates a force and therefore motion.
9. A DC motor transforms electrical energy into mechanical motion while a DC generator converts mechanical energy into electrical energy. Both devices work based on the principles of electromagnetic induction and using similar components.
10. AC electricity is generated by rotating a coil within a magnetic field. This motion induces a current in the coil. With a single coil, this produces a sinusoidally oscillating voltage, the hallmark of alternating current.

Essay Questions

1. Discuss the critical role of the split-ring commutator in the functionality of a DC motor. Explain how it ensures continuous rotation, and consider the consequence of its absence on the motor's performance. Include details of how the current reversal affects the direction of the torque.
2. Using the principles of electromagnetic induction, explain the similarities and differences between how a DC motor and a DC generator operate. Explain how both devices use similar structures, but accomplish opposite functions.
3. Describe the interaction of magnetic fields, moving charges, and resultant forces within a DC motor. Include a discussion of the left-hand rule, magnetic force, and the production of torque on the armature and explain why only the forces on AB and CD contribute to the rotation.
4. Explain how varying the current in the armature and the magnitude of the external magnetic field can affect the turning effect of a DC motor. Consider the implications of both increases and decreases of the variables.
5. Compare and contrast the methods of generating AC and DC electricity using the principles of electromagnetic induction. Include a discussion of the components used in each type of generator, paying specific attention to the role of the split-ring commutator.

Glossary

• Armature: The rotating part of a DC motor, typically a coil of wire, which carries the electric current and is acted upon by the magnetic field.
• Stator: The stationary part of a DC motor, often a permanent magnet, that provides the external magnetic field.
• Split-ring commutator: A mechanical device in a DC motor that reverses the direction of current in the armature every half rotation, allowing for continuous rotation.
• Electromagnetic induction: The phenomenon where a changing magnetic field induces an electric current in a conductor, as described by Faraday's law.
• Torque: A rotational force that causes an object to rotate around an axis; in a DC motor, it's the force that makes the armature spin.
• Left-hand rule: A mnemonic used to determine the direction of the magnetic force on a current-carrying wire in a magnetic field, based on the direction of the current and the magnetic field.
• DC Motor: A device that converts electrical energy into mechanical energy using direct current.
• DC Generator: A device that converts mechanical energy into electrical energy producing direct current.
• AC Electricity: Alternating current, where the direction of electrical flow changes periodically, usually in a sinusoidal fashion.
• Magnetic Field: A field of force generated by moving electric charges that exerts a force on other moving charges.

Video

 http://www.aps.org/programs/education/teachers/teachers-days/presentations/upload/090819-DC-motor-annotated-web.pdf Watch physicists Becky Thompson-Flagg and Ted Hodapp trade quips as they show how to take apart a small DC motor and find out how it works. They get the armature of the motor spinning with just a battery, a few wires, and a permanent magnet. The experiment in this video is the same one described in the DC Motor Annotated Activity Handout.

 

 

contribution to Wikipedia

Thumbnail	Date	Name	User	Size	Description
	08:56, 8 July 2011	Ejs Open Source Direct Current Electrical Motor Model Java Applet ( DC Motor ) 50 degree split ring.gif (file)	Lookang	884 KB
	08:56, 8 July 2011	Ejs Open Source Direct Current Electrical Motor Model Java Applet ( DC Motor ) 20 degree split ring.gif (file)	Lookang	1.21 MB
	08:56, 8 July 2011	Ejs Open Source Direct Current Electrical Motor Model Java Applet ( DC Motor ) 80 degree split ring.gif (file)	Lookang	858 KB

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For Teachers

1. http://iwant2study.org/lookangejss/05electricitynmagnetism_22electromagneticinduction/ejs/ejs_model_DCmotor10.doc Worksheet by Loo Kang Wee
2. http://iwant2study.org/lookangejss/05electricitynmagnetism_22electromagneticinduction/ejs/ejs_src_DCmotor10.zipsource codes

O level Syllabus

This helps students learn
explain how a current-carrying coil in a magnetic field experiences a turning effect and that the effect is increased by increasing
(i) the number of turns on the coil,
(ii) the current
discuss how this turning effect is used in the action of an electric motor
describe the action of a split-ring commutator in a two-pole, single-coil motor and the effect of winding the coil on to a soft-iron cylinder

Exercises:

The external magnetic field Bz can be varied using the slider Bz. When Bz is positive, it is in the direction vertically up. Vary Bz until it is negative, what is the direction of the Bz then?
The current comes from the battery higher potential end and travels in a wire forming a closed circuit and travels back to the lower potential end of the battery. When θ = 0o current flows from the battery higher potential end, to the top brush, to the RED split ring, through the coil loop in order ABCD, back to BLUE split ring, bottom brush and lower potential end of the battery. What is the direction of the current flow in wire AB? What is the direction of the current flow in wire CD? using Fleming's left-hand rule, deduce the relative directions of force acting on i) AB ii) CD iii) BC iv) DA. hint: note that Fmag = I*B*L*sin(I&B) may be useful.
By taking moments about the axle PQ, consider the forces on AB and CD, deduce the direction of the torque and the motion if the coil loop was initially at rest (ω = 0 deg/s). Select the suitable sliders of your choice and verify your hypothesis for 2 angles. Discuss with your partner what you have discovered. Ask your teacher if there are any problem/issues faced using this virtual lab.
Explain and show the equations involving T ( in earlier part of question), why the forces on wire BC and DA did not contribute to the calculation of rotating torque about axle PQ?
By considering the forces in the x direction for wire BC and DA, suggest what can happen to the coil loop if the forces are large enough.  Suggest why it does not happen in terms of the  properties of the wires in the coil loop.
Explain how a current-carrying coil in a magnetic field experiences a turning effect and that the effect is increased by increasing (i) the number of turns on the coil, (ii) the current (iii) increasing the magnitude of the external Bz field
After conducting some inquiry learning on the virtual DC motor model discuss how this turning effect is used in allowing the coil loop to rotate. You may right-click within a plot, and select "Open EJS Model" from the pop-up menu to examine the model equations of the motion. You must, of course, have EJS installed on your computer.
Describe the action of a split-ring commutator in a two-pole magnet setup, single-coil motor. Suggest the effect adding a soft-iron cylinder in the winding the coil.

Advanced Learner:

Please submit your remix model that model features that are not available in the existing virtual lab and share your model with the world through NTNUJAVA Virtual Physics Laboratory http://www.phy.ntnu.edu.tw/ntnujava/index.php?board=28.0. Impacting the world with your model today!

Software Requirements

Java

Credits

Fu-Kwun Hwang and Loo Kang Wee

 

Other resources

1. Physics on a Shoestring: A pop-up electric motor by Martin Monk 2003 Phys. Educ. 38 61 doi: 10.1088/0031-9120/38/1/404 http://iopscience.iop.org/0031-9120/38/1/404so this is how is looks like! adapted from Physics on a Shoestring: A pop-up electric motor by Martin Monk 2003 Phys. Educ. 38 61
2. http://www.fairlysimple.com/applets/21Electromagnetism.dcr like. give context to use of dc motor
3. http://www.walter-fendt.de/ph14e/electricmotor.htm most popular java applet on DC motor simulation by W. Fendt
4. http://webphysics.davidson.edu/physlet_resources/bu_semester2/c18_generators.html Wolfgang's explanation
5. http://imej.wfu.edu/articles/2001/2/02/demo/demo1-ac/ac.html Korea version of DC motor

Versions

1. http://iwant2study.org/lookangejss/05electricitynmagnetism_22electromagneticinduction/ejs/ejs_model_DCmotor10.jarby Fu-Kwun Hwang and Loo Kang Wee Java version from Digital Library
2. http://weelookang.blogspot.sg/2010/06/ejs-open-source-direct-current.html by Loo Kang Wee blogpost
3. http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1266.0 by Fu-Kwun Hwang and Loo Kang Wee Java version from NTNU Virtual Lab

4. http://physci.kennesaw.edu/mzoughi/Simulations.shtm using this model too http://physci.kennesaw.edu/ejs/ejs_TM_NTNU_DCmotor.jar Taha Mzoughi's implementation of the torque looks ok but i don't understand why his model the inertia of the DC motor affects the magnetic force.

5. http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=912.0 by Fu-Kwun Hwang original Java version

 

Frequently Asked Questions about DC Motors

1. How does a DC motor work to convert electrical energy into motion? A DC motor uses the principles of electromagnetism to create rotational motion. When an electric current flows through a wire placed in a magnetic field, it experiences a force. In a DC motor, a current-carrying coil (armature) is positioned within the magnetic field of a permanent magnet (stator). This interaction between the magnetic field and the moving charged particles (electrons) in the current results in a magnetic force, creating a torque that causes the armature to rotate.
2. What is the purpose of the split-ring commutator in a DC motor? The split-ring commutator is essential for continuous rotation in a DC motor. It acts as a switch, reversing the direction of the current in the armature every half rotation. Without the commutator, the torque would reverse every half-cycle, and the motor would simply swing back and forth. The commutator ensures the torque always acts in the same direction, enabling continuous rotational motion.
3. Explain the role of the stator and the armature in a DC motor? The stator is a fixed permanent magnet that creates the external magnetic field in the motor. The armature, also known as the rotor or coil, is a coil of wire that rotates within the stator's magnetic field. The armature is connected to the power supply via the commutator and brushes. The interaction between the magnetic field of the stator and the magnetic field generated by the current in the armature produces the force that causes the armature to rotate.
4. How does the left-hand rule relate to the operation of a DC motor? The left-hand rule is a tool used to determine the direction of the force on a current-carrying wire in a magnetic field. In a DC motor, the left-hand rule helps determine the direction of the magnetic force on the wires of the armature. When the current direction and magnetic field direction are known, the left-hand rule determines the direction of the force that causes the armature to spin. The rule dictates that the thumb points in the direction of the force, the index finger in the direction of the magnetic field, and the middle finger in the direction of the current.
5. Why is a torque produced on the armature of a DC motor? Torque is produced due to the magnetic forces acting on the current-carrying wires of the armature within the external magnetic field. Specifically, the forces on opposite sides of the coil are equal in magnitude but act in opposite directions, thus creating a rotational force, or torque, around the axle of the motor. The magnitude of the torque depends on the current, the magnetic field strength, the area of the loop, and the angle between the loop and the magnetic field.
6. How do you increase the turning effect or the force on the armature of a DC motor? The turning effect of a DC motor can be increased by several methods: (i) Increasing the number of turns in the coil (armature) increases the overall magnetic field and therefore the force; (ii) increasing the current flowing through the coil intensifies the magnetic field created by the coil, strengthening the interaction and the force; (iii) increasing the magnitude of the external magnetic field (Bz) results in a greater force. These factors combine to increase the torque and thereby the turning effect on the motor.
7. What is the relationship between electric motors and generators? Electric motors and generators are closely related devices that perform opposite functions. A motor converts electrical energy into mechanical energy (motion), while a generator converts mechanical energy (motion) into electrical energy. Both devices rely on the interaction between a wire coil and a magnetic field. In fact, the same physical device can be used as either a motor or a generator depending on whether a current is applied (motor) or the coil is spun (generator).
8. How is AC and DC electricity generated using the principles of electromagnetic induction? AC (alternating current) electricity is generated by spinning a coil of wire within a constant magnetic field. This induces an electromotive force (emf) in the coil, which varies sinusoidally as the coil rotates. The amplitude of the induced emf is determined by the speed of rotation, the number of turns in the coil, and the strength of the magnetic field. For generating DC (direct current) electricity, a split-ring commutator, similar to that in a DC motor, is used to maintain the same polarity of the voltage. In simple DC generators, the voltage level fluctuates; multiple loops out of sync are often used to produce a steadier voltage output. Another way to generate AC power is by rotating permanent magnets around a fixed coil, as seen in hydro-electric power plants.