Problem 15
Question
A photon has a wavelength of \(624 \mathrm{nm}\). Calculate the energy of the photon in joules.
Step-by-Step Solution
Verified Answer
The energy of the photon in Joules can be calculated by following three main steps which includes: conversion of wavelength to meters, calculation of frequency using speed of light and wavelength and finally, finding the energy using Planck's constant and frequency.
1Step 1: Convert Wavelength to Meters
Since the speed of light, c, is normally given in meters per second, and the wavelength is given in nanometers (nm), convert the wavelength from nanometers to meters. 1 meter = \(10^9\) nanometers, so \(λ = 624nm = 624 * 10^-9 m\).
2Step 2: Calculate the Frequency
Use the formula \(v = c / λ\) to compute the frequency. The speed of light, c, is approximately \(3.00 * 10^8 m/s\), so substituting the values we have \(v = (3.00 * 10^8 m/s) / (624 * 10^-9 m)\).
3Step 3: Compute the Energy
Use the formula for energy \(E = h * v\), where h is Plank's constant, which is approximately \(6.626 * 10^-34 Js\). Substitute the computed frequency from Step 2 into the formula to find the energy in Joules.
Key Concepts
Wavelength ConversionFrequency CalculationPlanck's ConstantSpeed of Light
Wavelength Conversion
Understanding how to convert wavelengths from one unit to another, such as from nanometers to meters, is crucial when dealing with light and other forms of electromagnetic radiation. A wavelength is the distance between identical points in the adjacent cycles of a waveform signal propagated in space or along a wire, which can be measured in various units. Nanometers (m\text{nm}) are often used to express wavelengths of light, especially in the field of optics, because they are suitable for reflecting the scale of visible light (which ranges approximately between 400 nm and 700 nm).
However, in many scientific formulas, such as those used in physics for calculating photon energy, the fundamental unit of length is the meter (\text{m}). Converting nanometers to meters is straightforward; since there are 1 billion nanometers in a meter, we use the relationship where 1 nm is equal to \(10^{-9}\) meters. For example, a photon with a wavelength of 624 nm is equivalent to 624 x \(10^{-9}\) meters.
To ease understanding and avoid confusion during calculations, always remember that conversion is simply a multiplication process, involving a conversion factor - in this case, the factor is \(10^{-9}\) for nanometers to meters.
However, in many scientific formulas, such as those used in physics for calculating photon energy, the fundamental unit of length is the meter (\text{m}). Converting nanometers to meters is straightforward; since there are 1 billion nanometers in a meter, we use the relationship where 1 nm is equal to \(10^{-9}\) meters. For example, a photon with a wavelength of 624 nm is equivalent to 624 x \(10^{-9}\) meters.
To ease understanding and avoid confusion during calculations, always remember that conversion is simply a multiplication process, involving a conversion factor - in this case, the factor is \(10^{-9}\) for nanometers to meters.
Frequency Calculation
The frequency of a photon is directly related to its wavelength by the inverse relationship described by the formula v = \(c / \lambda\), where \(v\) is the frequency, \(c\) the speed of light, and \(\lambda\) the wavelength. Frequency, measured in hertz (Hz), represents the number of times a wave's cycle repeats per second.
To calculate the frequency of a photon, one must know its wavelength and the speed at which the wave travels through the medium, which for light in a vacuum is approximately \(3.00 \times 10^8\) meters per second. With this information, simply divide the speed of light by the wavelength (in meters) to get the frequency in Hz. For a photon with a 624 nm wavelength, after conversion to meters, the frequency can be calculated, leading to a better understanding of the photon's characteristics such as energy.
To calculate the frequency of a photon, one must know its wavelength and the speed at which the wave travels through the medium, which for light in a vacuum is approximately \(3.00 \times 10^8\) meters per second. With this information, simply divide the speed of light by the wavelength (in meters) to get the frequency in Hz. For a photon with a 624 nm wavelength, after conversion to meters, the frequency can be calculated, leading to a better understanding of the photon's characteristics such as energy.
Planck's Constant
Planck's constant (\(h\)) is a fundamental quantity in quantum mechanics. It represents the proportionality constant between the minimum increment of energy, E, associated with a particle and the frequency, \(v\), of its associated wave. This constant has a value of approximately \(6.626 \times 10^{-34}\) joule-seconds (Js) and serves as a fundamental building block in formulas used for calculating the energy of a photon.
The relationship is given by the equation E = \(h \times v\), where E is the energy of the photon in joules. This equation implies that energy, like matter, can exhibit particle-like properties and is quantized, existing in discrete 'packets' or quanta. Understanding Planck's constant allows students to comprehend the particle-wave duality and the quantization of energy, which are key concepts within the realm of modern physics.
The relationship is given by the equation E = \(h \times v\), where E is the energy of the photon in joules. This equation implies that energy, like matter, can exhibit particle-like properties and is quantized, existing in discrete 'packets' or quanta. Understanding Planck's constant allows students to comprehend the particle-wave duality and the quantization of energy, which are key concepts within the realm of modern physics.
Speed of Light
The speed of light (denoted as \(c\)) is one of the most important constants in physics. It is the velocity at which light propagates through a vacuum and is exactly \(299,792,458\) meters per second (m/s). In calculations involving electromagnetic phenomena, the speed of light provides a link between space and time and appears in various key equations including those of wavelength and frequency calculations.
The finite, unvarying speed of light underpins Einstein's theories of special and general relativity and has further implications in understanding the nature of the universe. In practical terms for photon energy calculations, assuming the speed of light as \(3.00 \times 10^8\) m/s is a close approximation that simplifies the arithmetic, while still providing results that are accurate enough for most educational purposes.
The finite, unvarying speed of light underpins Einstein's theories of special and general relativity and has further implications in understanding the nature of the universe. In practical terms for photon energy calculations, assuming the speed of light as \(3.00 \times 10^8\) m/s is a close approximation that simplifies the arithmetic, while still providing results that are accurate enough for most educational purposes.
Other exercises in this chapter
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A photon has a frequency of \(6.0 \times 10^{4} \mathrm{~Hz}\). (a) Convert this frequency into wavelength (nm). Does this frequency fall in the visible region?
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