46. Visible Light and Colour

1. The Visible Light Spectrum

Visible light is a range of electromagnetic waves that our eyes can detect.

• Colors: Form a spectrum: Red, Orange, Yellow, Green, Blue, Indigo, Violet (RoyGBiv).

• Properties: * Red: Longest wavelength, lowest frequency.

  • Violet: Shortest wavelength, highest frequency.

• White & Black:

  • White Light: A combination of all wavelengths in the visible spectrum.

  • Black: The absence of light (all wavelengths are absorbed).

2. Colour of Objects

How an object appears depends on which wavelengths it reflects, absorbs, or transmits.

Opaque Objects (Do not transmit light)

• They absorb some wavelengths and reflect others.

• The color we see is the wavelength reflected.

  • A Red Apple reflects red and absorbs everything else.

  • Yellow Cheese reflects both red and green wavelengths (which combine to make yellow).

Transparent & Translucent Objects

• Transparent: Transmit most light (clear glass). Their color is determined by the wavelengths they transmit.

• Translucent: Transmit some light but scatter it, making the image blurry (frosted glass).

  • A Green Glass Bottle appears green because it transmits green light and absorbs other colors.

3. Colour Filters

Filters are materials that only transmit specific wavelengths of light.

Primary Colour Filters (Red, Green, Blue)

• They only allow their own color to pass through.

  • White light through a Green filter: Only green light is transmitted.

  • Looking at a Blue object through a Green filter: The object appears black because the blue light reflected by the object is blocked by the green filter.

Non-Primary Colour Filters (e.g., Yellow, Violet)

• They transmit their own wavelength plus the primary colors that mix to create that color.

  • Yellow Filter: Transmits yellow, red, and green light.

  • Violet Filter: Transmits violet, red, and blue light.

4. Summary Table: Object Interactions