Magnetism 1

Magnetism unlike poles attract a broken magnet creates new poles Magnetism = attraction or repulsion due to the arrangement of electrons like poles repel unlike poles attract a broken magnet creates new poles

Magnetic Field Magnetic Field area around a magnet where magnetic forces are detected field lines show direction of field (NS)‏

Use of Magnetism 1

Electromagnet Electromagnet strong, temporary magnet formed when current is passed through a coil of wire surrounding an iron core acts like a bar magnet when current is on

electromagnet rotates between the poles of a fixed magnet Poles on C. Motor Motor electrical energy  mechanical energy electromagnet rotates between the poles of a fixed magnet Poles on electromagnet switch in intervals making it spin

Creating Electricity 1

Electric Generator Electric Generator mechanical energy  electrical energy armature is rotated between magnet poles magnetic field induces a current in the wire coil

DC & AC Alternating Current (AC)‏ Direct Current (DC)‏ current flows in one direction dry cells Alternating Current (AC)‏ current reverses its direction at regular intervals electrical outlets

Transformer Transformer increases or decreases AC voltage primary coil AC produces a magnetic field that induces AC in the secondary coil voltage ratio = ratio of turns in each coil

D. Transformer Step-down Transformer Step-up Transformer increases the voltage more turns power plants Step-down Transformer decreases the voltage fewer turns household appliances (hairdryers, etc.)‏

Transformer Equation Is = Vp = Np Ip = Vs = Ns Primary Coil (p) – where the initial electrical current comes into the transformer Secondary Coil (s) – where the electricity leaves the transformer N - Number of turns in the coil

Transformers Step–up Transformer Vp < Vs Ip > Is Np < Ns Step-Down Transformer Vp > Vs Ip < Is Np > Ns

Example Problem A step-up transformer has a primary coil consisting of 200 turns and a secondary coil consisting of 3000 turns. The primary coil is supplied by an effective AC voltage of 90.0 V. What is the voltage in the secondary circuit? The current in the secondary circuit is 2.0 A. What is the current in the primary coil?

Example Continued Np = 200; Ns = 3000; Vp = 90.0 V; Is = 2.0 A Solve for Vs (Vs/Vp) = (Ns/Np)  (Vs/90) = (3000/200) Vs/90 = 15  Vs = 90 x 15 = 1350 V

Example Continued 2.0 / Ip = (90 / 1350) 2.0 / Ip = 0.0667 (multiply Ip out of denominator) 2.0 = 0.0667 x Ip (divide by 0.0667) 2.0 / 0.0667 = Ip = 30 A