# OCR - P3: Electric circuits

 P3.6 How do electric motors work? Background to the topic What you should be able to do: The magnetic fields of a current-carrying wire and a nearby permanent magnet will interact and the wire and magnet exert a force on each other. This is called the 'motor effect'. If the current-carrying wire is placed at right angles to the magnetic field lines, the force will be at right angles to both the current direction and the lines of force of the field. The direction of the force can be inferred using Fleming's left-hand rule. The size of the force is proportional to the length of wire in the field, the current and the strength of the field. The motor effect can result in a turning force on a rectangular current-carrying coil placed in a uniform magnetic field; this is the principle behind all electric motors. The invention and development of practical electric motors have made an impact on almost every aspect of daily life 1. Describe the interaction forces between a magnet and a current-carrying conductor to include ideas about magnetic fields In your practical lessons you will: Investigate the motor effect for a single wire in a magnetic field and apply the principles to build a simple electric motor. Build a simple electric motor and explain how it works. You should be able to: Describe and explain examples of uses of electric motors that have made significant improvements to people's lives. 2. Show that Fleming's left-hand rule represents the relative orientations of the force, the conductor and the magnetic field 3. Select and apply the equation that links the force (F) on a conductor to the strength of the field (B), the size of the current (I) and the length of conductor (l) to calculate the forces involved: force (N) = magnetic flux density (T) × current (A) × length of conductor (m) 4. Explain how the force on a conductor in a magnetic field is used to cause rotation in the rectangular coil of a simple electric motor - Detailed knowledge of the construction of motors not required