Spectrum Short notes and Selected PYQs | SmartScience ICSE Class 10

Dispersion: The splitting of white light into its constituent colors when passed through a prism.
Cause: Different colors of light travel at different speeds in a medium, causing different amounts of refraction.
Spectrum: The band of colors obtained (VIBGYOR: Violet, Indigo, Blue, Green, Yellow, Orange, Red).
Angle of Deviation: Varies with wavelength; violet deviates most, red deviates least.
Pure Spectrum: A spectrum in which colors do not overlap and are clearly distinct.

Newton's Experiment: White light dispersed by one prism can be recombined by an inverted second prism to produce white light.
Conclusion: White light consists of seven colors, and dispersion is due to refraction, not prism material.
Color Disk: A disk with seven colors rotated fast appears white, demonstrating recombination.
Importance: Proves that white light is composite, not monochromatic.

Monochromatic Light: Light of single wavelength/color (e.g., sodium vapor lamp - yellow).
Polychromatic Light: Light consisting of multiple wavelengths/colors (e.g., white light).
No Dispersion: Monochromatic light does not disperse when passed through a prism.
Applications: Monochromatic light used in optical experiments to avoid dispersion effects.

Definition: The complete range of all electromagnetic radiations arranged in order of wavelength or frequency.
Nature: All EM waves are transverse waves that travel at speed of light (3 × 10⁸ m/s) in vacuum.
Order (increasing wavelength): Gamma rays → X-rays → UV → Visible → Infrared → Microwaves → Radio waves.
Order (increasing frequency): Radio waves → Microwaves → Infrared → Visible → UV → X-rays → Gamma rays.
Visible Light: Only a small portion of EM spectrum visible to human eye (400-700 nm approximately).

Radio Waves: Longest wavelength, used in broadcasting, communication, radar.
Microwaves: Used in mobile phones, satellite communication, microwave ovens.
Infrared (IR): Heat radiation, used in remote controls, night vision, thermal imaging.
Visible Light: Enables vision, wavelength range ~400-700 nm (violet to red).
Ultraviolet (UV): Causes tanning, vitamin D production; harmful in excess (skin cancer). Used in sterilization.
X-rays: Used in medical imaging, airport security, detecting fractures.
Gamma Rays: Most penetrating, used in cancer treatment, sterilization of medical equipment, produced in nuclear reactions.

Energy and Frequency: Energy of EM wave is directly proportional to its frequency. Gamma rays have highest energy.
Penetrating Power: Increases with frequency. Gamma rays most penetrating, radio waves least.
Scattering: Shorter wavelengths scatter more (Rayleigh scattering). Blue light scatters more than red, explaining blue sky.
Harmful Effects: High-energy radiations (UV, X-rays, gamma rays) can damage cells and DNA.
Speed: All EM waves travel at same speed in vacuum but at different speeds in different media.

Spectrum