Physics Keypoints: Dispersion of light and colours; This study material is suitable for students sitting for the following exams: JAMB, WAEC, NECO, GCE, IJMB, and JUPEB. Light is a fascinating and complex phenomenon. It encompasses the dispersion of colors, the creation of pure spectrums, color mixing, the colors of objects, and the beautiful natural occurrence of rainbows.

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Additionally, understanding the electromagnetic spectrum allows us to explore the vast range of electromagnetic waves and their applications in our daily lives.

(a) Dispersion of Light and Colors

(i) Dispersion of White Light by a Triangular Prism

White light is actually a mixture of different colors. When white light passes through a triangular prism, it is dispersed. This happens because each color in the light spectrum has a different refractive index, which causes them to bend by varying amounts. As a result, the white light is separated into its constituent colors, forming a spectrum called a dispersion spectrum. The sequence of colors, in order of increasing wavelength, is red, orange, yellow, green, blue, indigo, and violet (ROYGBIV).

(ii) Production of a Pure Spectrum

To obtain a pure spectrum, a prism can be used to disperse white light. A single slit can also create a pure spectrum when light passes through it, producing a series of discrete lines or bands. This process is known as diffraction and is commonly used in spectroscopy to analyze the composition of light sources.

(iii) Color Mixing by Addition and Subtraction

Colors can be mixed in two primary ways: additive color mixing and subtractive color mixing.

• Additive Color Mixing: This method is used with colored light sources, such as those in television or computer screens. The primary colors of additive mixing are red, green, and blue (RGB). Mixing these colors in various intensities creates a wide range of colors.
• Subtractive Color Mixing: Subtractive mixing occurs when pigments or dyes are mixed. The primary subtractive colors are cyan, magenta, and yellow (CMY). Mixing these colors subtracts wavelengths and results in different colors. For example, mixing magenta and yellow pigments produces red.

(iv) Color of Objects and Color Filters

The color of an object is determined by the colors it reflects and the colors it absorbs. For example, an apple appears red because it reflects red light and absorbs other colors. Color filters work by selectively transmitting certain colors while blocking others. For instance, a red filter allows red light to pass through while absorbing other colors.

(v) Rainbow

A rainbow is a meteorological phenomenon that results from the dispersion, reflection, and refraction of sunlight in water droplets in the air. It forms a circular arc of colors, with red on the outer edge and violet on the inner edge. The order of colors in a rainbow is the same as in a dispersion spectrum: ROYGBIV.

(b) Electromagnetic Spectrum

(i) Description of Sources and Uses of Various Types of Radiation

The electromagnetic spectrum encompasses a wide range of electromagnetic waves, each with its own source and uses:

• Radio Waves: Generated by electronic circuits and used for communication and broadcasting.
• Microwaves: Produced by microwave ovens and used in telecommunications, radar, and satellite communication.
• Infrared Radiation: Emitted by hot objects and used in remote controls, thermal imaging, and cooking.
• Visible Light: The spectrum of light our eyes can perceive, used in vision and a wide range of technologies.
• Ultraviolet (UV) Radiation: Emitted by the sun and used in sterilization, tanning, and fluorescent materials.
• X-rays: Produced in X-ray machines and used in medical imaging, security screening, and materials analysis.
• Gamma Rays: Emitted by nuclear reactions and used in medical imaging, radiation therapy, and nuclear physics.

Understanding the electromagnetic spectrum allows us to harness various forms of radiation for countless applications, from communication to healthcare and scientific research.

In conclusion, the dispersion of light, colors, and the electromagnetic spectrum are interconnected and play fundamental roles in our daily lives. From understanding why objects have certain colors to the vast range of electromagnetic waves and their applications, these concepts are crucial in both science and technology.