The Motor Effect
Overview
Stop reading for a moment and count the electric motors within ten metres of you. The fan in a laptop. The buzz in a phone. The pump in a fridge, the drum of a washing machine, the passenger window of a car, the disc that spins a hard drive, the wipers, the fuel pump. A family car carries more than thirty and almost nobody could name five. Every one runs on a single idea small enough to fit in a sentence: put a current through a wire that is already sitting in a magnetic field, and something shoves the wire sideways.
This lesson is about that shove. You will find out where it comes from, why it acts sideways to both the current and the field rather than along either, and why the magnet gets shoved just as hard the other way. You will learn to read a force direction straight off an arrangement with nothing but your own left hand, a skill the specification names outright. Then you will bend the wire into a loop and watch a push turn into a spin, which is the whole of an electric motor in one step. One thing has to be said before any of it: on this course every single statement of this topic is printed in bold type, which means the whole of it is Extension Tier material. The next section explains exactly what that does and does not mean for you.
Objectives
- A current carrying conductor has a magnetic field around the wire. When a current carrying conductor is placed in a magnetic field so that it cuts lines of magnetic force, the magnet and the conductor exert a force on each other. This is called the motor effect. The conductor will not experience a force if it is parallel to the magnetic field.
- The size of the force can be increased by: increasing the strength of the magnetic field; increasing the size of the current; increasing the length of the conductor in the magnetic field.
- The direction of the force is reversed if either the direction of the current or the direction of the magnetic field is reversed. Students should be able to identify the direction of the force using Flemings left-hand rule.
- A coil of wire carrying a current in a magnetic field tends to rotate. This is the basis of an electric motor.
Mind map
This topic is mapped out so you can see how the ideas connect.
Open the mind map in the app
Lesson Note
Complete Note Available on the Green Bridge App
Get the Green Bridge CBT app on your phone or computer for the complete IGCSE library: past papers, mark schemes, mind maps, flashcards and audio lessons.
Lesson Evaluation
Congratulations on completing the lesson on The Motor Effect. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- In Fleming's left-hand rule, what does the first finger point along? A. The direction of the force on the conductor B. The direction of the magnetic field C. The direction of the conventional current D. The direction of the flow of electrons Answer: B
- A straight wire lies between the poles of a magnet, parallel to the magnetic field lines. A large current is passed through the wire. What force acts on the wire? A. No force at all B. A force at right angles to the field C. A force along the direction of the current D. A force twice the size of the force when the wire is at right angles to the field Answer: A
- Which change would NOT increase the size of the force on a current-carrying wire in a magnetic field? A. Using a stronger magnetic field B. Increasing the current in the wire C. Increasing the length of the wire that lies inside the field D. Turning the wire so that it lies along the magnetic field lines Answer: D
- The current in a wire in a magnetic field is reversed, and the magnet is also turned round so that its poles trade places. What happens to the direction of the force on the wire? A. It is reversed B. It is unchanged C. It becomes zero D. It turns through 90 degrees Answer: B
- Why does a rectangular coil carrying a current in a magnetic field tend to rotate? A. Its two long sides carry current in opposite directions, so they are pushed in opposite directions on opposite sides of the axle B. Its two long sides carry current in the same direction, so they are pushed the same way C. The magnet is attracted to the coil D. The coil becomes an induced magnet and is attracted to the pole faces Answer: A
Work through these questions in the app
Work through these questions in the app
Recommended Books
Practice Mock Questions
Want to practice mock questions on The Motor Effect? Download the Green Bridge CBT app to access mock questions and full practice assessments for this topic.
Download The App On Google Playstore
Everything you need to excel in your exams
