Sources Of Light

• Objects that give off their own light are called luminous objects, such as the Sun, a burning candle, a bulb, and the stars.
• Objects that do not give off their own light are called non-luminous objects, such as the Moon, a book, or a mirror.
• The Sun is the biggest natural source of light and heat for the Earth.
• Artificial sources of light, made by people, include a bulb, a torch, a candle, and a tube light.
• Light travels in a straight line and travels far faster than sound.

Level 1 - Core idea

Verbal: Objects that produce their own light are luminous, like the Sun and a bulb. Objects that only reflect light, like the Moon, are non-luminous. Light travels in straight lines and moves much faster than sound.

Symbolic: luminous object -> makes own light; non-luminous object -> only reflects light from elsewhere

Visual: On a dark night, a torch (luminous) lights up a wall, and the Moon (non-luminous) shines only because it reflects sunlight.

Level 2 - NCERT anchor

NCERT Looking Around 5 links this to everyday observation of the Sun, Moon, and lamps as sources of light in daily life.

Why does the Moon appear to shine at night even though it does not make its own light?

Step 1 - The Moon is a non-luminous object.
Step 2 - Sunlight falls on the Moon's surface.
Step 3 - The Moon reflects this sunlight toward Earth.
Answer: The Moon shines because it reflects sunlight, not because it makes its own light.

You see lightning in the sky before you hear the thunder that happened at the same instant. Why?

Step 1 - Both light and sound start together during lightning.
Step 2 - Light travels far faster than sound.
Step 3 - So light from the flash reaches your eyes almost instantly.
Answer: Light reaches you first because it travels much faster than sound.

• Name two luminous objects and two non-luminous objects.
• Why does the Moon appear bright at night?
• Give one example of an artificial source of light.
• In what path does light normally travel?
• Stretch: Why do we see lightning before we hear thunder?

Revision tip: Look around your room and label five objects as luminous or non-luminous.

Open the Practice tab for graded questions on Sources Of Light.