Practical Physics: Analysing the Force in Motor Coils


Discover how universal motors optimize torque regardless of current direction, suitable for both AC and DC applications.



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Unlock the fundamentals of electromagnetic interactions in motors with our engaging PDF slide file, titled “Practical Physics: Analysing the Force in Motor Coils.” This meticulously crafted educational resource aims to deepen high school students’ understanding of how forces within motor coils influence performance and efficiency.

Discover the Dynamics of Motor Coils

Our slides delve into the science behind motor coils, starting with a clear explanation of magnetic fields and their interaction with electric currents. We take learners on a journey through the basic principles, such as the right-hand rule and Fleming’s left-hand rule, ensuring they grasp the direction of forces involved.

Engage with Interactive Learning

We’ve designed each slide to challenge and engage learners. Interactive elements like animations demonstrate the effect of altering variables such as current strength, coil density, and magnetic field intensity on the force experienced by a motor coil. This dynamic approach helps students visualize and understand complex concepts more effectively.

Simplify Complex Concepts

The resource breaks down complex formulas and theories into understandable segments. By presenting information in a step-by-step format, we make challenging topics accessible. Each section builds upon the previous one, reinforcing learning and ensuring students grasp the intricacies of motor coil forces without feeling overwhelmed.

Quizzes and Practical Examples

To solidify understanding and assess comprehension, we incorporate quizzes and practical examples throughout the presentation. These activities encourage students to apply their knowledge in various scenarios, enhancing their problem-solving skills and preparing them for more advanced studies in physics and engineering.

A Tool for Educators

For educators, this slide file is an invaluable teaching asset. It comes equipped with detailed notes and guidance on how to effectively deliver content to stimulate curiosity and participation. The slides are also adaptable for different teaching approaches, whether it’s in a classroom, as part of a flipped lesson, or for remote learning sessions.

Optimised for Classroom Engagement

Designed with the classroom environment in mind, “Practical Physics: Analysing the Force in Motor Coils” enhances learning experiences and fosters academic excellence. Its clear visuals, concise definitions, and engaging content are optimized to keep students interested and involved throughout the learning process.


This PDF slide file is not just a teaching tool; it’s a comprehensive educational experience that transforms theoretical knowledge into practical understanding. It’s an essential resource for any educator looking to inspire and educate their students on the fascinating topic of motor coils and the forces at play within them.

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Additional information

Motors and Generators

Question 16
What is the difference between a DC motor and a universal
Universal motors contain electromagnets with windings in
series with the coil, so that if the direction of the current
reverses, the direction of the magnetic field also reverses.
This means that the torque on the coil will always act in the
same direction, regardless of the direction of the current
through the coil, so that an AC power supply can cause the
motor to turn.

Question 17
(a) What is the purpose of the brushes in a DC motor?
The brushes provide a sliding contact between the
commutator on the motor’s armature and the power supply.↙
(b) Why is graphite commonly used for these brushes?
Graphite, as well as being conductive, is a lubricant.
It keeps the motor’s commutator slippery, so that it does not
slow down when in contact with the brushes. ↙

Question 18
A transformer has a primary coil with 2000 turns. If the
transformer is designed to step down a 10 kV signal to a
240 V signal, find the number of turns in the secondary coil.
48 turns

Question 19
An electric current of 5 A flows through a hair dryer that has
a resistance of 75 Ω.
(a) What power does the hair dryer radiate?
(b) What current would be required to increase the hair
dryer’s power by a factor of 100?

Question 20
It takes about 78 kJ of energy to bring 250 mL of water to the
boil. An electric kettle is able to boil this much water in 40 s.
(a) Find the kettle’s power, assuming no energy is lost.
(b) Find the current through the kettle if it has a resistance
of 20 Ω.

Question 21
(a) Write down an equation showing the flux through a generator coil of n turns and area A forming an angle of
with a magnetic field of strength B.
(b) Write down an equation for the emf induced in the coil
in terms of the flux through it.

Question 22
A current of 0.5 A flows through 25 turns of wire on a
motor’s coil. The coil is in a magnetic field of strength 0.02 T and has an area of 0.03 m2. Find the torque on the coil when:
(a) the coil is parallel to the magnetic field.
(b) the coil is perpendicular to the magnetic field.