42. Visible & Ultraviolet Light

GCSE Physics: Visible & Ultraviolet Light

1. Visible Light

Visible light is the range of the electromagnetic spectrum that human eyes can detect.

Characteristics

• Colors: Different wavelengths appear as different colors.

• Order: Remember the order from longest to shortest wavelength using ROY G BIV (Red, Orange, Yellow, Green, Blue, Indigo, Violet).

Uses: Optical Fibers

• Function: Thin glass or plastic fibers that transmit pulses of light over long distances.

• Mechanism: Light bounces back and forth along the fiber through specular reflection.

• Advantages:

  • Transmits much more information than copper wires.

  • Signals are less likely to be distorted.

  • Data travels very quickly over long distances.

2. Ultraviolet (UV) Radiation

UV radiation has a shorter wavelength and higher frequency than visible light.

Fluorescence

• Definition: Certain chemicals absorb UV light and re-emit the energy as visible light.

• Fluorescent Lights: UV radiation is generated inside the bulb and absorbed by a phosphorus coating, which then emits visible light. These are highly energy-efficient.

• Fluorescent Paints: These appear extra bright because they are actually emitting their own light rather than just reflecting it.

Security and Identification

• Security Pens: Used to mark property with "invisible" ink that only glows under UV light.

• Banknotes & Passports: Contain special UV-sensitive markings to help detect forgeries.

Other Uses

• Sunbeds & Suntans: UV radiation is emitted by the sun (and artificial sunbeds) to give skin a tan, though overexposure leads to sunburn.

• Sterilization: UV light is used to sterilize water by destroying microorganisms.

3. Summary Table