The given statement is false. The efficiency of a full wave rectifier using a center tapped transformer is not twice that of a full wave bridge rectifier. In fact, the efficiency of both rectifiers is similar, with slight differences due to the different configurations.

1. Full Wave Rectifier using Center Tapped Transformer:
- In a full wave rectifier using a center tapped transformer, the input AC voltage is applied to the center tap of the transformer, and two diodes are connected to the opposite ends of the secondary winding.
- During the positive half-cycle of the input AC voltage, the upper diode conducts and allows the current to flow through the load.
- During the negative half-cycle, the lower diode conducts and again allows the current to flow through the load.
- As a result, the entire AC waveform is rectified, and both halves of the input cycle contribute to the output.
- However, there is a voltage drop across the diodes, resulting in a slightly lower output voltage compared to the input voltage.
- The efficiency of this rectifier is typically around 81% to 86%.

2. Full Wave Bridge Rectifier:
- In a full wave bridge rectifier, four diodes are connected in a bridge configuration, with the input AC voltage connected to the two opposite corners of the bridge.
- During the positive half-cycle of the input AC voltage, two diodes conduct and allow the current to flow through the load.
- During the negative half-cycle, the other two diodes conduct and again allow the current to flow through the load.
- Similar to the center tapped rectifier, both halves of the input cycle contribute to the output, and there is a voltage drop across the diodes.
- The efficiency of this rectifier is also typically around 81% to 86%, which is similar to the center tapped rectifier.

Conclusion:
The efficiency of a full wave rectifier using a center tapped transformer is not twice that of a full wave bridge rectifier. Both rectifiers have similar efficiencies, typically ranging from 81% to 86%.

Same efficiency