Answer:
75 %
Step-by-step explanation:
Total energy capacity of battery = 12 V
energy converted into electrical = 9 V
(Note: this energy will be utilized by the battery )
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Energy converted into thermal = 12 V - 9 V = 3V
Note: this energy will be wasted by the battery \
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Efficiency of battery is determined by fraction of energy which is actually utilized out of total energy
since only 9 v of energy is utilized out of 12 v available energy
efficiency of battery = 9/12 = 3/4 = 0.75
Efficiency of battery in percentage = 0.75 * 100 % = 75 %