Transformers

Transformers

1. What do they do?

   • Transformers change the POTENTIAL DIFFERENCE- but only AC potential difference

2. Step-up transformers

   • Has 2 coils, the PRIMARY AND SECONDARY, joined with an IRON CORE
     • Step the voltage UP
       • MORE TURNS on the SECONDARY COIL than the primary coil

3. Step-down transformers

   • Has 2 coils, the PRIMARY AND SECONDARY, joined with an IRON CORE
     • Step the voltage DOWN
       • MORE TURNS on the PRIMARY COIL than on the secondary

4. How do they work?

   • Transformers work by electromagnetic induction
     • 1. The primary coil PRODUCES A MAGNETIC FIELD which stays WITHIN THE IRON CORE. This means NEARLY ALL of it passes through the SECONDARY COIL and hardly any is lost
       • 2. Because there is ALTERNATING CURRENT in the PRIMARY COIL,the field in the iron core is constantly CHANGING DIRECTION- induces a CHANGING MAGNETIC FIELD
         • 3. This RAPIDLY CHANGING MAGNETIC FIELD is then felt by the SECONDARY COIL
           • 4. The changing field INDUCES an ALTERNATING POTENTIAL DIFFERENCE across the secondary coil (with the same frequency as the alternating current in the primary)- ELECTROMAGNETIC INDUCTION of a potential difference

5. Iron core

   • 1. Iron core purely for transferring the CHANGING MAGNETIC FIELD from the primary coil to the secondary
     • 2. NO ELECTRICITY flows round the iron core

6. Coils

   • Transformers have more turns on one coil than another
     • 1. The RELATIVE NUMBER OF TURNS on the 2 coils determines whether the potential difference is induced in the secondary is GREATER or LESS than the potential difference in the primary
       • 2. In a STEP-UP TRANSFORMER, the POTENTIAL DIFFERENCE across the SECONDARY COIL is GREATER than the POTENTIAL DIFFERENCE across the PRIMARY COIL
         • 3. In a STEP-DOWN TRANSFORMER, the POTENTIAL DIFFERENCE across the SECONDARY COIL is LESS than the potential difference across the PRIMARY COIL
           • 4. Direct current= nothing out of the secondary coil- no constantly changing magnetic field- no induction in secondary coil- transformers only work with AC

7. Switch-mode transformers

   • Used in chargers
     • 1. Switch-mode transformers are a type of transformer that OPERATE AT HIGHER FREQUENCIES than traditional transformers
       • 2. Usually operate at between 50 kHz and 200 kHz
         • 3. Because they work at HIGHER FREQUENCIES- made much LIGHTER, SMALLER than traditional transformers that work from a 50 Hz MAINS SUPPLY
           • 4. This makes them more useful in things like MOBILE PHONE CHARGERS and pOWER SUPPLIES e.g. for laptops
             • 5. MORE EFFICIENT- VERY LITTLE POWER