1. Load Transformers These are electromagnetic devices which can ‘step up’ or ‘step down’ ac voltages. A 240 volt supply can be converted to (for example) either 2400 volts or 24 volts using a transformer. They work as shown below: Primary Coil with number of turns = ‘ N 1 ’ Soft iron laminated Core. (Iron for maximum flux, soft for easy magnetisationLaminated to prevent ‘eddy currents’) The alternating voltage causes an alternating current in the primary coil. This causes an alternating flux in the core Secondary Coil with number of turns = ‘ N 2 ’ This causes an alternating current to flow in the load. Alternating Voltage V1V1 The secondary coil is now linked to a changing flux, so an alternating voltage is induced in it

2. The Transformer Formula The Voltages at each end of the transformer, and the numbers of turns in the coils at each end are related by the formula: Example: A transformer has 200 turns on its primary coil and 1000 turns on its secondary coil. The voltage applied to the primary coil is 240 volts ac. What is the voltage at the secondary coil NB transformers do not work on DC, only on AC, because they must have CHANGING voltages and currents

3. Transformer Efficiency Most transformers are almost 100% efficient, so: Useful power out = Total power in The formula for Power is: P = VI So for a transformer which is100% efficient: For transformers which are not 100 % efficient, the standard formula for efficiency is:

4. Load Transformers These are electromagnetic devices which can ‘step up’ or ‘step down’ ac voltages. A 240 volt supply can be converted to (for example) either 2400 volts or 24 volts using a transformer. They work as shown below: Primary Coil with number of turns = ‘ N 1 ’ Soft iron laminated Core. (Iron for maximum flux, soft for easy magnetisation)Laminated to prevent ‘eddy currents’ The alternating voltage causes an alternating current in the primary coil. This causes an alternating flux in the core Secondary Coil with number of turns = ‘ N 2 ’ This causes an alternating current to flow in the load. Alternating Voltage V1V1 The secondary coil is now linked to a changing flux, so an alternating voltage is induced in it

5. The Transformer Formula The Voltages at each end of the transformer, and the numbers of turns in the coils at each end are related by the formula: Example: A transformer has 200 turns on its primary coil and 1000 turns on its secondary coil. The voltage applied to the primary coil is 240 volts ac. What is the voltage at the secondary coil

6. Transformer Efficiency Most transformers are almost 100% efficient, so: The formula for Power is: So for a transformer which is100% efficient: For transformers which are not 100 % efficient, the standard formula for efficiency is: