Teacher notes - Prior knowledge • Describe the shape of a field around a straight wire, solenoid • Describe that a current carrying wire at right angles to a magnetic field experiences a force • Use Fleming’s left hand rule to predict the direction of a force on a current carrying conductor • Use the right hand rule to predict the direction of field around a current carrying conductor motors P2 Success Criteria • Build a simple dc motor • Use Fleming’s left hand rule to explain how your motor spins • Use the idea of combining fields to explain how your motor spins 1 Minute Presentation (Mr) (Fleming’s) (Cat) Teacher notes • Provide class with a selection of motors collected from old / broken household items (eg. hairdryer, food mixer, tape recorder, video player, drill etc.) Thinking about motors • What do they have in common? • How do you think they work? • Where do you think they are used? Teacher notes • Can demo ‘paper clip motor’, ‘screw motor’ and or ‘spiral motor’. Several other examples on you tube http://www.youtube.com/watch?v=UhMkUOWaN3M Teacher notes • Introduce the motor kit apparatus. • Take pupil suggestions as to how to constuct. • Pupil activity: Build motors • 2 challenges with appropriate help/explanations follow 25-Mar-16 25-Mar-16 CHALLENGE • Use Fleming’s LEFT hand rule to explain how your motor works. Motion (Mr) Field (Fleming’s) (cat) N S N = current out of page = current into page S N S http://www.youtube.com/watch?v=FjNnRyLexNM CHALLENGE • Draw fields around the wires and between the magnets. • How do they combine to make your motor spin? Direction of current N Direction of field S extension The right hand rule • You can work out the direction of the field using your right clenched fist. Direction of current • Reversing the direction of the current will reverse the magnetic field direction. Direction of field Forces caused by fields SOUTH DECREASED FIELD INCREASED FIELD MOTION NORTH N Field reduced S Field increased Use key ideas from today’s lesson to annotate your diagram Homework activity • What is a split ring commutator? • Why do practical motors have curved pole pieces?