Modern NiMH rechargeable batteries of size AA have a maximum charge capacity of

Question

Modern NiMH rechargeable batteries of size AA have a maximum charge capacity of 2300 mAh and an emf equal to 1.20 V. A flashlight has three of these batteries connected in series. The 3.6 V bulb in the flashlight draws a current of 0.3 A. Assume that both the emf and the current do not change with time.

Part A

Calculate how long the flashlight will operate using these rechargeable batteries.

Modern NiMH rechargeable batteries of size AA have a maximum charge capacity of 2300 mAh and an emf equal to 1.20 V. A flashlight has three of these batteries connected in series. The 3.6 V bulb in the flashlight draws a current of 0.3 A. Assume that both the emf and the current do not change with time.

Part A

Calculate how long the flashlight will operate using these rechargeable batteries.

Explanation / Answer

The energy produced by each battery is,

E = (2300 mAh)(1.20V) = (2.3*3600 s)(1.20 V) = 9936 J

The total energy produced by three batteries is,

E = 3(9936J) = 29808 J

The energy consumed by buld per hour is,

       P = VI = (3.6 V)(0.3A) = 1.08 W

The power is defined as,

      P = E/t

Therefore, the flashlight will operate for a time is,

    t = E/P = 29808 J/1.08 W = 27600 s (or) 7.67 hours.

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