P3.3 KEEPING THINGS MOVING 3

P3.3 KEEPING THINGS MOVING 3

1. TRANSFORMERS

   • STEP UP TRANSFORMER:
     • Have MORE TURNS on Secondary coil than primary coil
     • Potential Difference across Secondary coil is GREATER than potential difference across the Primary coil
   • STEP DOWN TRANSFORMER:
     • Have MORE TURNS on Primary coil than secondary coil
     • potential difference across Secondary coil is LESS than the potential difference across the Primary coil
   • IRON CORE:
     • carries magnetic field
     • No electricity flows around the iron core

2. HOW TRANSFORMERS WORK:

   • 1. Primary coil produces magnetic field which stays within iron core
   • 2. so nearly all of it passes through the secondary coil
   • 3. AC current in Primary coil, field in iron core is constantly changing direction
     • changing magnetic field
   • 4. Rapidly changing magnetic field felt by secondary coil
   • 5. changing field induces Alternating Potential difference across secondary coil
     • (electromagnetic induction)
   • to induce V need changing field so CANT use DC only AC

3. SWITCH MODE TRANSFORMER

   • WHAT? type of transformer that operate @ higher frequencies than traditional transformers
   • operate at HIGH FREQUENCY, often between 50 kHz - 200 kHz
   • much lighter & smaller than traditional transformers working from a 50 Hz mains supply
     • so Useful as MOBILE PHONE CHARGERS & power supplies (laptop)
   • use very little power when they are switched on but no load is applied
     • so more EFFICIENT