Question

Which has the higher energy: blue light or violet light?

Short answer

Violet light has higher energy than blue light.

Step-by-step solution

Understand the Concept of Light Frequency and Energy

The energy of electromagnetic waves, including light, is directly related to their frequency. The formula to determine the energy of a photon is given by \[ E = h \cdot f \] where \( E \) is the energy, \( h \) is Planck's constant (approximately \( 6.626 \times 10^{-34} \) Js), and \( f \) is the frequency of the light. Higher frequency means higher energy.

Identify the Frequency of Blue and Violet Light

The electromagnetic spectrum consists of various colors of light, with violet light having higher frequency than blue light. In general, blue light has a wavelength range of about 450 to 495 nm, while violet light ranges from 380 to 450 nm. Since energy is directly related to frequency and inversely related to wavelength (\( f = \frac{c}{\lambda} \)), violet light, with a shorter wavelength, has a higher frequency than blue light.

Apply the Energy Formula

Using the relationship \( E = h \cdot f \) and knowing that the frequency \( f \) is inversely proportional to the wavelength \( \lambda \), we conclude that shorter wavelengths (higher frequencies) result in higher energy. Thus, violet light, having a higher frequency than blue light, possesses higher energy.

Key concepts

Light Frequency

Light frequency is a crucial concept in understanding how we perceive different colors within the electromagnetic spectrum. The frequency of light refers to how frequently the waves of light pass a specific point in a given amount of time. It is measured in Hertz (Hz), which is equivalent to one cycle per second. In the spectrum of visible light, different colors correspond to different frequencies.
Light frequency is directly linked to its energy, which means the higher the frequency, the more energy the photons of that light possess. This is why colors that have higher frequencies, such as violet and ultraviolet, carry more energy compared to colors with lower frequencies, like red and orange. The visible light spectrum on the electromagnetic scale is a small part that ranges from around 400 terahertz (THz) for red light to about 800 terahertz for violet light.
In practice, this means that when we are comparing colors, such as blue and violet, the higher frequency of violet light indicates it has more energy.

Photon Energy

Photon energy is a fundamental characteristic of light that can be understood through the equation \[ E = h \cdot f \]where \( E \) represents the energy of a photon, \( h \) is Planck's constant (approximately \( 6.626 \times 10^{-34} \) Js), and \( f \) is the frequency of the light. This relationship highlights how critical frequency is in determining the energy carried by light photons.

• **Planck's Constant:** It is a physical constant that plays a significant role in the quantum world, particularly in the calculation of photon energy.
• **Frequency:** Directly proportional to energy, meaning as frequency increases, so does the photon energy.

For instance, when considering blue and violet light, violet light's higher frequency suggests a correspondingly higher photon energy. This principle also illustrates why the effects of UV radiation are more pronounced than that of blue light, due to its higher energy potential.

Wavelength and Frequency Relationship

The relationship between wavelength and frequency is an inverse one. This means that as the wavelength decreases, the frequency increases. The formula representing this relationship is \[ f = \frac{c}{\lambda} \]where \( f \) stands for frequency, \( c \) is the speed of light in a vacuum (approximately \( 3 \times 10^8 \) m/s), and \( \lambda \) is the wavelength.
This inverse relationship is paramount in understanding the electromagnetic spectrum. For example, violet light, which has a wavelength range of 380 to 450 nanometers (nm), exhibits a higher frequency compared to blue light, with a wavelength range of 450 to 495 nm. As frequency increases with decreasing wavelength, the energy of the light also increases.

• **Speed of Light:** Constant factor that helps in calculating the frequency when the wavelength is known.
• **Inverse Relationship:** Essential for understanding why shorter wavelengths equate to higher frequencies and consequently higher energies.

This relationship explains why violet light is more energetic than blue light despite their closeness on the spectrum. The shorter the wavelength, the higher the energy.