Final answer:
A condenser can significantly increase the efficiency of a turbine, however, the answer choices given (50%, 30%, 80%, 15%) do not directly relate to a standard increase attributable solely to the addition of a condenser. Efficiency gains from condensers are substantial but vary based on original power plant conditions.
Step-by-step explanation:
A condenser is used in power plants to increase the efficiency of a turbine by converting the exhaust steam from the turbine into liquid to be cycled back into the steam generator or boiler. This process creates a lower pressure on the exhaust side of the turbine, which increases the turbine's efficiency.
While the exact percentage can vary depending on the original design and operating conditions, none of the options provided (50%, 30%, 80%, 15%) directly correspond to a typical increase in efficiency due to a condenser alone.
However, as a rule of thumb, the use of a condenser generally increases the overall efficiency of thermal power plants by a significant margin.
Looking at the other examples provided, a generic representation of efficiency improvement is shown. For instance, the upgrade of turbines in a coal-powered power plant is assumed to improve efficiency by 3.32%, which is a more realistic figure for such enhancements.
The subsequent calculations in those examples would show the benefits in terms of electrical energy produced and the reduction of heat transfer to the environment due to such an upgrade.