"The battery of a mobile phone is rated as $4.2 \mathrm{~V}, 5800 \mathrm{~mAh}$. How much energy is stored ir it when fully charged?"

Question

Accepted Answer

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To find the energy stored in the battery, follow these steps:

Convert mAh to Ah:

The battery capacity is given as 5800 mAh. Since

$1\,\text{Ah} = 1000\,\text{mAh},$

we have

$5800\,\text{mAh} = 5.8\,\text{Ah}.$

Calculate energy in watt-hours (Wh):

The energy in Wh is given by the product of the voltage and the capacity in Ah. Thus,

$\text{Energy (Wh)} = 4.2\,\text{V} \times 5.8\,\text{Ah} = 24.36\,\text{Wh}.$

Convert watt-hours to joules (J):

Since

$1\,\text{Wh} = 3600\,\text{J},$

the total energy in joules is:

$$24.36\,\text{Wh} \times 3600\,\text{J/Wh} = 87,696\,\text{J} \approx 87.7\,\text{kJ}.$$

Thus, the energy stored in the battery when fully charged is about 87.7 kJ.

The correct answer is Option A: 87.7 kJ.

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The battery of a mobile phone is rated as $4.2 \mathrm{~V}, 5800 \mathrm{~mAh}$. How much energy is stored ir it when fully charged?