Electromagnetic Induction,Motors and Transformers
It’s common for some students to struggle when learning about transformers, motors and electromagnetic induction. It requires the combination of an understanding of the relationships between current, potential difference (and resistance) as well as the interaction between magnetic fields and charge carrying conductors. It is also common for the magnetic effect of a current, the electric motor and the generator (dynamo) to be taught a separate phenomena rather than all part of the same set of ideas and so this can cause challenges as the connections between these are not clear in the student's mind.
The building of electric motors can be a fun and engaging activity but equally the physical complexity of the activity can create barriers to understanding. The simple electric motor shown first in the list below (the homopolar motor) can help to show the interaction between a current carrying ‘wire’ and a magnetic field as a principle although can become quite complex if you look too closely at the magnetic fields involved.
The PhET simulation Faraday’s Electromagnetic Lab is very helpful is walking students and teachers through the ideas that are at the core of all of these ideas. The resources below should provide practical ideas to introduce these topics to students.
Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS, SSERC or recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance
Electric Motor
This little practical for students is ace, they will love it! Using just a battery, a magnet and a coil of wire, students make their own electric motor. Just make sure you use the new neodymium magnets, as older, traditional magnets simply aren’t strong enough.
You could use it in lots of different ways and here are two suggestions. Use it as a hook to engage students with the topic by getting them to make the motor before attempting any explanation. Alternatively, students could build the motor after having completed some theoretical work. Challenge them to present to each other or a small group, how this motor works.
Introducing Magnetic Fields and the Electric Motor Effect
Using the same kit as in the resource above, here’s a rather different approach to introducing electric motors. Rather than explain or give instructions about how to build a motor, students are encouraged to investigate and share their ideas with each other in small groups, before feeding back to the rest of the class at the end of the lesson. It’s a nice approach if you have the time since students are likely to be intrigued and want to know more. Make sure that you provide the new, strong neodymium type magnets. The resources consist of a lesson plan and teacher notes. The equipment they are provided with allows them to build a motor along the lines of the motor in activity in the activity at the top of this page so choose for yourself how to use this practical work best.
Motors and Electromagnetism
This material from the Science Enhancement Programme will prove valuable to teachers looking for a bit of support when teaching motor and dynamos. It starts by explaining the motor effect clearly and goes on to suggest demonstrations and practical work with lots of teaching tips. You are unlikely to have enough time to use all the suggestions for investigative work but two activities are particularly recommended:
• Building an electric motor. The MUTR kit referred to here is still available from Mindsets. Go to www.mindsetsonline.co.uk and search for self assembly motor kit. It’s recommended because all the parts are clearly visible and the completed motors always work.
• Building a loudspeaker.
Mini DC Generator
First published well over a decade ago, this booklet looks it’s age but the mini generator it is referring to is still alive and kicking and available from mindsets for less than £10 ex VAT Find it at http://www.mindsetsonline.co.uk and type "mini dc motor" into the search facility. Students will enjoy building the motors and the booklet suggests some simple, and not so simple activities, for using them. The book gives plenty of background physics including the use of diodes to rectify the voltage.
Electromagnetic Induction *suitable for home teaching*
Alom Shaha does a good job of explaining electromagnetic induction in this film and his demonstration makes a great introduction to the topic. The equipment he uses can be built fairly easily but similar set ups can be readily purchased from school suppliers. Students will see the immediate connection between the energy put in by the operator and the output of the bulb and the spinning magnets are very visible which aids understanding too.
Transformer Simulation
This simulation was written by practising teachers to help students see what happens when you change the primary input or turn on a transformer. You could use it after students have built transformers for themselves so that they can recongnise the different parts of the device. Follow this up with the worksheet where students carry out the calculations for themselves.
Power Lines
This film talks teachers through a classic demonstration; why transformers are used in conjunction with power lines. It’s great for showing exactly how to set up and operate the model and it will help teachers to feel more confident if they are demonstrating it for the first time. There are some good safety tips at the end of the film and notes on an alternative approach in the accompanying teacher notes.
You can use this at the start of the topic to introduce the need for transformers or alternatively use it towards the end so that students can apply what they have already learnt.
Most schools will already have all the equipment necessary for the demonstration but, as it is a bit fiddly and time consuming to set up, they may like to consider purchasing a kit such as that available from Mindsets (National Grid Transmission Model) which makes the whole process even easier and does lots of other stuff besides.
Physics on Earth and Mars
Hold on to those old TV sets! These films from the National Space Centre provide a novel and really interesting context in which to explore the motor effect. The TV and magnets demonstration is highly recommended and really helps students to understand how the motor effect comes about. Anu Ojha’s expertise allows him to provide clear, lucid explanations and the two follow up films (Motors and Solar Weather, and Mars Electric Field) take the key ideas further and apply them to situations students (and many teachers) are unlikely to have come across before.
