3.2.3 Electric Lamp

Last updated at April 25, 2026 by

What is Electric Lamp?

It is a device that produces light when electric current passes through it.

Key Facts and Examples
  • Incandescent lamp has thin wire called filament inside glass bulb .
Example: Torch bulb, table lamp bulb, ceiling light bulb
  • Filament gets hot and glows to produce light when current passes .
Example: Torch light glowing, room light bulb glowing
  • LED has no filament inside but two terminals .
Example: LED bulb, LED torch, LED indicator lights
  • LED positive terminal is attached to longer wire .
Example: Red LED, green LED, blue LED with long and short wires
  • LED negative terminal is attached to shorter wire .
Example: LED components showing wire length difference
Incandescent Lamp vs LED Property Incandescent Lamp LED Filament Has thin wire filament No filament inside Light source Hot glowing filament Electronic light emission Terminals Two thick support wires Two wires - long and short Direction Works both directions Works one direction only Heat Gets very hot Stays cool

Activity 3.4: Examining Incandescent Lamp (Page 30)

What you need:

  • Torchlight with incandescent lamp

What to do:

  • Step 1: Confirm torchlight uses incandescent lamp
  • Step 2: Examine the lamp in torch
  • Step 3: Look for thin wire in glass bulb
  • Step 4: Switch on torch and observe which part glows
  • Step 5: Take out lamp with teacher help
  • Step 6: Inspect lamp from all sides

Observations

What you see:

  • Thin wire filament visible inside glass bulb
  • Filament glows when torch is switched on
  • Two thick wires support the filament
  • One thick wire connects to metal case at lamp base
  • Other thick wire connects to metal tip at centre of base

Why this happens:
We have studied that incandescent lamps use filament to produce light . This is why filament glows .

  • Electric current heats the filament
  • Hot filament glows and produces light
How Incandescent Lamp Works Current flows Through filament wire Filament heats Wire gets very hot Hot wire glows Produces bright light Lamp lights up!

🌟 Fascinating Fact: Sometimes, an incandescent lamp does not glow even when connected to a cell. We say the lamp has 'fused' usually due to a broken filament. A broken filament stops the flow of current, preventing the lamp from glowing.

Working vs Fused Lamp Working Lamp Fused Lamp Complete filament Broken filament Current flows No current flow Lamp glows Lamp does not glow

Activity 3.5: Examining LED (Page 30)

What you need:

  • LED of any colour

What to do:

  • Step 1: Take an LED of any colour and observe
  • Step 2: Look inside for filament
  • Step 3: Notice the length of two wires attached to the LED
  • Step 4: Compare wire lengths

Question (Page 30): Do you see any filament inside it?

Answer:
We have studied that LED is different from incandescent lamp . This is why it has no filament .

  • LED uses electronic method to produce light
  • No thin wire is needed for light production

Question (Page 30): Do you find that one wire is longer than the other?

Answer:
We have studied that LED has two terminals with different wire lengths . This is why we can see the difference.

  • Longer wire connects to positive terminal
  • Shorter wire connects to negative terminal
LED Terminal Identification Positive Terminal Negative Terminal Longer wire Shorter wire Connect to + of battery Connect to - of battery Current enters here Current exits here

Observations

What you see:

  • No filament visible inside LED
  • One wire is longer than the other wire
  • LED body is small and solid

Why this happens:
We have studied that LED works differently from incandescent lamps . This is why design is different .

  • LED needs correct polarity to work
  • Wire lengths help identify positive and negative terminals
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