A parallel plate capacitor with plate separation \( 5 \, \text{mm} \) is charged up by a battery. It is found that on introducing a dielectric sheet of thickness \( 2 \, \text{mm} \), while keeping the battery connections intact, the capacitor draws \( 25\% \) more charge from the battery than before. The dielectric constant of the sheet is \( \_\_\_\_\_\_\_\_ \).
