Question

The spectrum of white light ranging from red to violet is called a continuous spectrum because (a) different colours are seen as different bands in the spectrum (b) the colours continuously absorb energy to form a spectrum (c) the violet colour merges into blue, blue into green, green into yellow and so on (d) it is a continuous band of coloured and white light separating them.

Short answer

The correct answer is (c) because the continuous spectrum is characterized by the seamless merging of each color into the next.

Step-by-step solution

Understanding the Continuous Spectrum

A continuous spectrum is one where there are no gaps; all colors blend seamlessly into one another. In the context of white light, when it is passed through a prism, it splits into its component colors (such as red, orange, yellow, green, blue, indigo, and violet) without any interruption or discrete bands between them.

Evaluating the Options

To solve this exercise, consider the nature of a continuous spectrum and which option best describes why the spectrum of white light is considered continuous. Option (a) states different colors appear as distinct bands, which is characteristic of a non-continuous spectrum, whereas option (b) provides an irrelevant explanation about colors absorbing energy. Option (d) is incorrect as it suggests the presence of white light separate from the colored bands. Therefore, consider option (c) which correctly explains the seamless merging of one color into another.

Selecting the Correct Answer

Based on the definition of a continuous spectrum, option (c) is the correct answer because it accurately describes how each color in the white light spectrum merges into the next without any gaps, creating a continuous range of colors.

Key concepts

White Light Dispersion

When white light enters a prism, a fascinating transformation occurs. This phenomenon, known as white light dispersion, is the process whereby a beam of white light is separated into its constituent colors. Imagine holding a prism up to sunlight. As the light passes through the angled surfaces of the prism, each wave of light bends—or refracts—at a slightly different angle, depending on its wavelength.

Red light, with its longer wavelength, bends the least, while violet light, with its shorter wavelength, bends the most. This spread of colors is what we observe as a rainbow-like band, a continuous spectrum ranging from red to violet. The reason for this is that white light is actually a combination of all the visible colors. Dispersion occurs due to the varying degrees to which different wavelengths of light are slowed down and refracted as they enter a denser medium, like glass or water.

Prism and Light Spectrum

The relationship between a prism and light spectrum is a visual delight that has fascinated scientists and artists alike for centuries. A prism, typically a triangular block of transparent material, acts as a gatekeeper, bending and spreading out the components of white light. The glass prism's geometry is particularly important because it determines the angles at which different wavelengths of light are refracted.

As white light passes through a prism, the light within separates into a multicolored band called the spectrum. The most remarkable aspect of this is the creation of a seamless, gradual transition from one color to the next—the very essence of what we call a continuous spectrum. This observation laid the groundwork for understanding that light consists of a range of electromagnetic waves, each color representing a different wave frequency.

Visible Light Spectrum

What we perceive with our naked eye is just a small part of the electromagnetic spectrum, known as the visible light spectrum. This spectrum is composed of the array of colors that can be observed by the human eye. These colors include red, orange, yellow, green, blue, indigo, and violet, commonly remembered by the acronym ROYGBIV.

The visible light spectrum falls within wavelengths approximately ranging from 380 to 750 nanometers. Each color has a specific wavelength—red has the longest, violet the shortest. When white light is dispersed, each wavelength reveals itself as a distinct hue, yet they blend without interruption to create what we perceive as 'white' light. This seamless blending is why the spectrum is known as 'continuous', distinguishing it from other types of spectra that may have gaps or lines, as seen in the emission spectra of gases. The continuous nature of the visible light spectrum is essential for various optical phenomena and technologies, including photography, spectroscopy, and even digital displays.