Technology has significantly helped humans overcome natural obstacles by:
1. Improving Accessibility: Technologies like bridges, tunnels, and railways have made previously inaccessible terrains reachable.
2. Agricultural Advancements: Irrigation, fertilizers, and machinery have enabled farming in arid and difficult regions.
3. Weather Predictions: Satellites and forecasting systems help mitigate disasters like cyclones and floods.
A battery of emf \( E \) and internal resistance \( r \) is connected to a rheostat. When a current of 2A is drawn from the battery, the potential difference across the rheostat is 5V. The potential difference becomes 4V when a current of 4A is drawn from the battery. Calculate the value of \( E \) and \( r \).