JEE Main 2025 — Current Electricity Question with Solution

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.