NCERT Solutions Curiosity Chapter 3 Activity 3.5: Let us observe — Electric lamp
Book page 27 Updated on2026-09-05
Q1.
Take an LED of any colour (Fig. 3.6) and observe. Do you see any filament inside it?
Answer
No. Unlike an incandescent lamp, an LED has no filament (Fig. 3.6).
Inside the small coloured dome you can only see a tiny cup holding a speck of material, joined to the two wires. That speck gives out light directly when current passes through it — nothing has to get red-hot first.
Did you know? LED stands for Light Emitting Diode. Because it does not waste energy in heating a filament, an LED gives the same brightness while using far less electricity, and it lasts much longer. That is why most new torches, street lights and home bulbs are LEDs.
Q2.
Notice the length of two wires attached to the LED. Do you find one of those longer than the other?
Answer
Yes. Of the two wires coming out of an LED, one is clearly longer than the other, and this difference in length is a code for the terminals.
Wire of the LED
Terminal it is
Must be joined to
Longer wire
Positive (+) terminal
+ terminal of the battery
Shorter wire
Negative (–) terminal
– terminal of the battery
Why it happens: Current can pass through an LED in one direction only. The makers therefore leave one wire longer so that you can identify the direction even without any printing on the LED. Join it the wrong way round and the LED simply stays dark — it does not glow dimly, it does not glow at all.