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Two starships, the Enterprise and the Constitution, are approaching each other head-on from a great distance. The separation between them is decreasing at a rate of \(722.5 \mathrm{~km} / \mathrm{s}\). The Enterprise sends a laser signal toward the Constitution. If the Constitution observes a wavelength of \(\lambda=670.3 \mathrm{~nm}\), what wavelength was emitted by the Enterprise?

Short Answer

Expert verified
The emitted wavelength was approximately 671.9 nm.

Step by step solution

01

Understanding the Problem

We know two starships are moving towards each other, and we need to find the emitted wavelength from one of the starships, the Enterprise, given the wavelength observed by the Constitution. This scenario involves the Doppler effect for light.
02

Doppler Effect Formula

For light, the Doppler effect for wavelength when two objects are moving towards each other is given by the formula \( \lambda' = \frac{\lambda}{1 - \frac{v}{c}} \), where \( \lambda \) is the observed wavelength, \( \lambda' \) is the emitted wavelength, \( v \) is the relative velocity, and \( c \) is the speed of light.
03

Assign Known Values

We have the observed wavelength \( \lambda = 670.3 \) nm, the relative velocity \( v = 722.5 \) km/s, and the speed of light \( c = 299,792 \) km/s. These values will be substituted into the Doppler effect formula.
04

Substitute Values into Formula

Substituting the known values into the Doppler effect formula, we get:\[ \lambda' = \frac{670.3}{1 - \frac{722.5}{299,792}} \] This formula will allow us to solve for the emitted wavelength \( \lambda' \).
05

Calculate the Emitted Wavelength

Calculate the denominator:\[ 1 - \frac{722.5}{299,792} \approx 1 - 0.00241 = 0.99759 \]Then, calculate the emitted wavelength:\[ \lambda' = \frac{670.3}{0.99759} \approx 671.9 \text{ nm} \]
06

Conclusion

The emitted wavelength \( \lambda' \) from the Enterprise is approximately 671.9 nm.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Wavelength
Wavelength is a fundamental concept in understanding how light and other forms of electromagnetic radiation propagate through space. It represents the distance between consecutive peaks (or troughs) in a wave, typically measured in nanometers (nm) for visible light. In the context of the Doppler effect, wavelength plays a pivotal role in determining how we perceive the emitted light from an object moving towards us or away from us.

When an object emitting light is moving towards an observer, the waves are compressed, leading to a shorter observed wavelength, resulting in what is known as "blue shift." Conversely, if the object moves away, the waves stretch, resulting in a longer wavelength, or "red shift." In our exercise, the challenge is to find the emitted wavelength when a starship moves toward another, causing the observed wavelength to change.

Understanding the relationship between the emitted and observed wavelengths helps us detect motion in astronomy and physics, thus providing insights into cosmic velocity and distances of celestial bodies.
Light
Light is a type of electromagnetic radiation that is visible to the human eye. It travels in waves and is characterized by its wavelength and frequency. Visible light in the electromagnetic spectrum ranges from about 380 nm (violet) to 750 nm (red).

When we solve problems involving the Doppler effect for light, we focus on how the wavelength of light changes due to relative motion between the source and the observer. This principle not only helps in everyday observations but is also crucial in astrophysics for understanding how celestial bodies move.

Through exercises like the given problem, students can appreciate how light, when emitted by high-speed moving objects like starships or stars, reveals valuable information about the dynamics and properties of the universe. The changes in light's wavelength can help us determine their velocity and direction of travel, pushing the boundaries of what we can observe from far-off places.
Relative Velocity
Relative velocity plays a crucial role in the study of motion and waves. It is the velocity of an object as observed from another moving object. In the context of the Doppler effect problem, it is the effective speed at which the two starships are moving towards each other.

Calculating the relative velocity is essential because it affects how we perceive the wavelength of light. In our problem, the relative velocity given is 722.5 km/s, which signifies how fast the separation between the starships decreases. This relative movement causes a shift in the observed wavelength of light due to the Doppler effect.

Relative velocity helps us understand true movement between two bodies, crucial for navigation in space and interpreting signals from fast-moving sources. It allows us to decode the real speed and direction of such sources based on how their emitted light is perceived.
Speed of Light
The speed of light in a vacuum is a constant and one of the fundamental constants of nature. It is approximately 299,792 kilometers per second (km/s), or about 186,282 miles per second. This constant speed is central to many theoretical frameworks in physics, including the theory of relativity.

When examining the Doppler effect, the speed of light ( c ) is crucial for calculating changes in wavelength as an object moves relative to an observer. It serves as a denominator in the Doppler formula, affecting the perception of light's wavelength as emitted and observed by different sources moving at high speeds.

Understanding the speed of light enables us to calculate the delay in receiving signals, determine distances in space, and comprehend how light's behavior changes under different conditions. As seen in the problem at hand, using the speed of light involves precise calculations that help us deduce the physics of high-speed travel and communication across vast distances in space.

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Most popular questions from this chapter

A typical home may require a total of \(2.00 \times 10^{3} \mathrm{kWh}\) of energy per month. Suppose you would like to obtain this energy from sunlight, which has an average daily intensity of \(1.00 \times 10^{3} \mathrm{~W} / \mathrm{m}^{2}\). Assuming that sunlight is available \(8.0\) hours per day, 25 days per month (accounting for cloudy days) and that you have a way to store energy from your collector when the Sun isn't shining, determine the smallest collector size that will provide the needed energy, given a conversion efficiency of \(25 \%\).

Michelson's Speed Measurement In 1926 Albert Michelson measured the speed of light with a technique similar to that used by Fizeau. In place of a toothed wheel, Michelson used an eight-sided mirror rotating at \(528 \mathrm{rev} / \mathrm{s}\), as illustrated in Figure 15.38. The distance from the rotating mirror to the fixed reflector was \(35.5 \mathrm{~km}\). If the light completed the \(71.0-\mathrm{km}\) round-trip in the time it took the mirror to complete one-eighth of a revolution, what is the speed of light?

A TV screen is half magenta, half green. The screen has \(3,000,000\) pixels, each with one red color dot, one green color dot, and one blue color dot. How many red dots are lit? How many green dots are lit? How many blue dots are lit?

Ablation In radiofrequency (RF) ablation, a small needle is inserted into a cancerous tumor. When radiofrequency oscillating currents are sent into the needle, ions in the neighboring tissue respond by vibrating rapidly, causing local heating to temperatures as high as \(100^{\circ} \mathrm{C}\). This kills the cancerous cells but, because of the small size of the needle, relatively few of the surrounding healthy cells. A typical RF ablation treatment uses a frequency of \(750 \mathrm{kHz}\). What is the wavelength that such radio waves would have in a vacuum?

Moon-Based Reflector One experimental apparatus placed on the Moon's surface by Apollo 11 astronauts was a reflector that is used to measure the Earth-Moon distance with high accuracy. A laser beam on Earth is bounced off the reflector, and its round-trip travel time is recorded. If the travel time can be measured to within an accuracy of \(0.030 \mathrm{~ns}\), what is the uncertainty in the measured Earth-Moon distance?

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