Lesson: Magnets and Compasses 101

Year 8 Physics Lesson Plan

Learning outcomes for ALL students ("MUST" and "SHOULD"):

*Understanding that there are only 4 naturally occurring - and metallic - materials commonly in existence

*Discovering the basic properties of magnets - that like poles repel and unlike poles attract.

*To plot the magnetic field pattern around a simple bar magnet using a plotting compass.

Book References:

Physics for You - Keith Johnson 

Experiments/Demonstrations:

*Experiment 1: Magnetic or non-magnetic: need 10 items of which 4-5 should be magnetic (nickel, iron, steel, cobalt?, 1or 2p coin).  Must be labelled else Al and Zn get confused etc. OR order up H.Shaw Magnet sets - just metals and all labelled A-L for them!

*Experiment 2: Blocking Magnetic Fields: Clamp stand holding a magnet.  Tie a paperclip to a 1m length of string, which you tie to the base of the clamp stand.  The paperclip should be able to levitate about 1cm below the magnet.  Offer in the space between: sheet of paper or very thin sheet of iron/steel etc.

*Demo 1: Attraction or Repulsion: Need clamp stand (from Experiment 2) with paper cradles for free standing rotation of magnet hanging within.  Offer a second magnet such that alike poles cause rotation away and unlike poles cause rotation towards the student.  

*Experiment 4: Plotting magnetic fields: Drawing around a magnet and tracking the magnetic field with a small circular plotting compass.

*Demo 2: Magnetic fields around a bar magnet: 'Magnetic Field Pattern Window': transparent plastic with Fe filings trapped inside oil and bar magnet is placed on the outside (I don't think this is very good) OR plastic casings with small grid of compasses and you can connect these together in 3 planes to see the field in 3D (see Notes - Magnetic Field Demonstrator  - fantastic piece of kit)).

Lesson notes: (brief, relevant description of lesson where Class Practicals (CP), Class Demos (CD), Worksheets (WS) etc can be referred to by the initials and the numbers assigned in boxes above)

Starter:

1. Back of books: True/False quiz.  No releasing of answers - we will return to this at the end of the lesson. Last question leads on to the first Main. 

Main:

1.  Experiment 1: Magnetic or non-magnetic.  (WS Are you Magnetic?) Test the materials and record in a table.  Should discover that Iron (steel), Nickel and Cobalt and Magnetic.  Also some rare earth elements, such as Gadolinium that are magnetic (don't need to worry about Ferro- and Para- magnetism differences at this age!). Recording the appearance is a useful skill - they cannot distinguish between anything that is silvery and shiny - despite the difference in surface quality, tarnish, specula reflection and weight! 
2. Experiment 2: Blocking Magnetic Fields.  Get students to set up themselves.  Leave the paperclips levitating whilst they draw and annotate their diagrams.  Introduce student to Free Body Diagrams by drawing one of the forces involved - get them to work out what the forces involved are.  Reinforce that the stationary aspect of their set up implies no NET force. 
3. Demo1 : Attraction or Repulsion: using the same clamp stand etc.  Again once done, draw the set up - get them to use lots of colour to make the experience more memorable and less tedious. This could be done as an experiment, but they don't get anything from it and it takes up valuable time. 
4. Now make sure that each student has a magnet and a compass and remove the clamp stands and paperclip-strings.  They will play with these endlessly otherwise. 

Plenary:

1. Experiment 4: Plotting magnetic fields: This is very hard for quite a few, so be incredibly encouraging and praise even the worst of diagrams but the best of efforts! Allocate about 25 minutes. Use WS Plotting the Magnetic Field around a Bar Magnet to really structure what they are going to do.  In fact, print the sheet as A5 sized on the left hand side of a blank piece of paper, so that they can draw around their magnet on the blank side and move their compass around - whilst drawing a circle for where the compass was and then adding and LINE to mark where the compass arrow was.  Can use the Phet - Magnets and compasses simulation to help. Once this is done, as a class use Demo 2  - draw over the set up, so that they understand how to draw the field lines and then put arrows on, determining the N and S poles of their magnet.
2. Highlight the rules for drawing lines: lines may not touch, there is 2 fold symmetry, direction of arrows is N->S, only one set of straight lines  - all others are curved. When drawing the field lines on the board, colour coordinate each rule with a feature of the diagram: 1) 1 set of straight lines, 2)2 sets of symmetry, arrows N->S , 4) no crossing nor touching of lines.

Language for learning, including key words, units and formulae:

iron filings

Suggested homework tasks (differentiated where appropriate):

1. P6b/3 Magnetic Field Questions
2. Lonsdale Questions - History of the compass