NCERT Solutions Curiosity Chapter 4 Activity 4.6: Let us construct — Voltaic cell
Book page 56 Updated on2026-09-05
Q1.
Connect the LED between the copper wire of the first lemon and the iron nail of the last lemon, using connecting wires. What do you observe? Does the LED glow?
Answer
If the LED is the right way round, it glows — faintly, but clearly visible in a shaded corner of the room. A glowing LED indicates that your cell is working.
The lemon cells are joined copper-to-nail in a chain; the LED goes between the copper of the first lemon and the nail of the last.
Why it glows: in each lemon the copper wire and the iron nail are two different electrodes and the lemon juice is the electrolyte, so each lemon is a small Voltaic cell. Chemical reactions at the two metals drive a current round the outside circuit, and that current is what makes the LED glow. Joining several lemons in a chain adds their pushes and gives enough to light the LED.
Q2.
If the LED does not glow, reverse its connections. Does the LED glow now?
Answer
Yes. Turn the LED round in the circuit and it lights up.
Why the direction matters: an LED lets current pass through it in one direction only. As you learnt earlier, current can pass through the LED only when its positive terminal (the longer wire) is connected to the positive terminal of the battery, and its negative terminal (the shorter wire) is connected to the negative terminal. If it was joined the wrong way round, no current passed and there was nothing to see — the cell was working all along.
Tip: an LED that fails to glow is therefore not proof that the lemon cell has failed. Always try reversing the LED before deciding that your set-up does not work.