A 1.5 v cell supplies 0.20 a to a lamp for seven hours before the lamp goes out. what is a sensible estimate for the initial chemical energy content of the cell?
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Let us neglect all the heat losses during the supply.
We assume that the cell voltage will not change during the discharge.
According to the law of conservation of energy:
The initial chemical energy content of the cell is the same as the electrical energy transferred to the lamp.
The last energy supplied to the lamp is given by :
E = Pt
Where P is the power of the lamp and t the time for discharge in seconds.
Power of the lamp equals :
P = VI, where V is the voltage and I the current supplied.
Adjusting the equation :
E = VIt
Convert the 7 hours to seconds
7 × 3600 = 25200
Substituting in the formula :
E = 0.2 × 1.5 × 25200 = 7560J
Answer :
7560 J
We assume that the cell voltage will not change during the discharge.
According to the law of conservation of energy:
The initial chemical energy content of the cell is the same as the electrical energy transferred to the lamp.
The last energy supplied to the lamp is given by :
E = Pt
Where P is the power of the lamp and t the time for discharge in seconds.
Power of the lamp equals :
P = VI, where V is the voltage and I the current supplied.
Adjusting the equation :
E = VIt
Convert the 7 hours to seconds
7 × 3600 = 25200
Substituting in the formula :
E = 0.2 × 1.5 × 25200 = 7560J
Answer :
7560 J
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