physics

physics

1. magnetism

   • induced magnet
     • When a piece of unmagnetised magnetic material touches or is brought near to the pole of a permanent magnet, it becomes a magnet itself.
   • magnetic material
     • iron
     • nickel
     • cobalt
   • magnetic field
     • how the size and direction of a conductor in a magnetic field can be changed?
       • This can be done when making simple motors by wrapping more wire around, increasing the p.d. or using stronger magnets.
     • A magnet creates a magnetic field around it. You cannot see a magnetic field, but you can observe its effects. A force is exerted on a magnetic material brought into a magnetic field. The force is a non-contact force because the magnet and the material do not have to touch each other.
   • magnetic flux density
     • Magnetic flux density is defined as the amount of magnetic flux in an area taken perpendicular to the magnetic flux's direction. An example of magnetic flux density is a measurement taken in teslas.

2. motor effect

   • right hand thumb rule
     • The direction of the cross product may be found by application of the right hand rule as follows: The index finger points in the direction of the velocity vector v. The middle finger points in the direction of the magnetic field vector B. The thumb points in the direction of the cross product F.
   • what is it?
     • The motor effect is the term used when a current-carrying wire in the presence of a magnetic field experiences a force
   • why a motor spins
     • Inside an electric motor, permanent magnets are set onto a ring surrounding a coil of wire. When the appliance's switch is flicked on, electrons flow through the wire, turning it into an electromagnet. The attractive and repulsive forces of the permanent magnets around it make the electromagnet spin
   • fleming's left hand rule
     • thumb = thrust or motion. index finger = field. middle finger = current
   • how a moving coil loud speaker and headphones work
     • When a fluctuating electric current flows through the coil, it becomes a temporary electromagnet, attracted and repelled by the permanent magnet. As the coil moves, it moves the cone back and forth, pumping sound waves into the air

3. induced potential

   • generators
     • what they do
       • generate electric current from kinetic energy
     • ways of increasing the size of the induced potential difference of a generator
       • Increase the amount of coils around the solenoid
     • how to make a simple generator out of wire and permanent magnets
       • Step 1 Make up two cardboard circles about 3cm in diameter (1-2 mm thick). Carefully pierce a hole in the middle of the circles. Find a large (10-15 cm long, 6 mm wide) clean (unrusty) nail having a large head. Thread one of the circles onto the nail and push right up to the head. Step 2 Cover the last 3-4 cm of the nail with a single layer of insulation tape (leave the nail head uncovered). Push the second circle onto the nail but only so far as the insulation tape. Add more tape onto the other side of the circle to fix the circle in place. You should now have a ready made 'spool' on which to wind the coil. Step 3 Obtain some thin insulated copper wire (say 25m or so of 30SWG, aprox. 0.3mm diameter) leave about 20-30 cm free and start to wind turns onto the insulated part of the nail between the two circles. Wind 1000-1500 turns (the exact number does not matter much and will depending on how neat you can get them on before they spill over the restraining cardboard circles). Leave a

4. national grid

   • transformers