Refer to the Activity 3 in the chapter. Start with distilled water. The LED would not glow. Add two drops of some acid to distilled water and check the glow of LED. Add two more drops and check the intensity of the glow. Repeat the activity 5 to 6 times by adding 2 drops of the same acid each time. Do you see any difference in the intensity of glow with increasing acid content of water? What can be inferred from the above observations? Repeat the entire activity by taking a solution of baking soda and adding drops of it to distilled water instead of acid. Write differences and similarities.

Explain the process of coating copper on iron key. Draw the circuit diagram.

Make a battery from four lemons and test it with a LED in the circuit.

In many of the activities in this chapter, we have used a tester made up of LED. Can we avoid LED and use something else as a tester? Magnetic compass needle could be an alternative tester. We know that when we take a current carrying wire near magnetic compass needle, it shows deflection. Use this property to make a tester of magnetic compass needle. You may refer to the following figure.

How do you appreciate the efforts of Luigi Galvani and Alessandro Volta in discovering a cell and making a stored Electric energy available to human beings?