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A pesky \(1.5 \mathrm{mg}\) mosquito is annoying you as you attempt to study physics in your room, which is \(5.0 \mathrm{~m}\) wide and \(2.5 \mathrm{~m}\) high. You decide to swat the bothersome insect as it flies toward you, but you need to estimate its speed to make a successful hit. (a) What is the maximum uncertainty in the horizontal position of the mosquito? (b) What limit does the Heisenberg uncertainty principle place on your ability to know the horizontal velocity of this mosquito? Is this limitation a serious impediment to your attempt to swat it?

Short Answer

Expert verified
The uncertainty in velocity due to the Heisenberg uncertainty principle is expected to be incredibly small, considerably smaller than typical mosquito speeds, thus it does not significantly impede the attempt to swat the mosquito. The precise numbers can be obtained by plugging into the equations given, but irrespective of the numbers, quantum uncertainty doesn't noticeably affect everyday phenomena like a mosquito flying in a room.

Step by step solution

01

Calculate Uncertainty in Position

The first part of the question asks for the uncertainty in the position of the mosquito. Looking at the problem context, the maximum uncertainty in the position of the mosquito is the width of the room, because the mosquito could be anywhere between one wall and the other. Since the room is \(5.0 \, m\) wide, the uncertainty in position, denoted by \(Δx\), is equal to \(5.0 \, m\).
02

Apply Heisenberg's Uncertainty Principle

Next, we are to find the limit on our ability to know the mosquito's horizontal velocity. This is where the Heisenberg Uncertainty Principle comes into play, which is given by the following relation: \(Δx \cdot Δp ≥ h/4π\) Where Δx is the uncertainty in position, Δp is the uncertainty in momentum (which is the product of mass and velocity), and h is Planck's constant (\(6.62607015 × 10^{-34} m^2 kg / s\)). Simplifying this equation for velocity, we get: \(Δv ≥ h/(4πmΔx)\) Where m is the mass of the mosquito and Δx is the uncertainty in the mosquito's position.
03

Calculate Uncertainty in Velocity

Substituting the known values for Planck's constant (\(h = 6.62607015 × 10^{-34} m^2 kg / s\)), the mass of the mosquito (\(m = 1.5 \, mg = 1.5 × 10^{-6} kg\)), and the uncertainty in the mosquito's position (\(Δx = 5.0 \, m\)), we can calculate the minimum uncertainty in the velocity of the mosquito.
04

Evaluate physical significance

Finally, to determine whether or not this uncertainty is a serious impediment to swatting the mosquito, it is useful to compare the numerical resultant with typical mosquito flying speeds (they usually fly at speeds of up to 2 m/s). If the uncertainty in the mosquito's velocity is larger than typical mosquito speeds, then the Heisenberg Uncertainty Principle would indeed be a significant obstacle. However, it's likely to be smaller, suggesting that quantum uncertainty doesn't noticeably affect the attempt to swat the mosquito.

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Key Concepts

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

Quantum Mechanics
Quantum mechanics is a fundamental theory in physics, providing a comprehensive description of physical properties at very small scales, such as atoms and subatomic particles. Unlike classical physics, which can accurately predict the behavior of objects we interact with daily, quantum mechanics reveals the probabilistic nature of particles. It operates on principles quite different from classical mechanics. For instance, particles can exist in multiple states simultaneously until observed, a phenomenon known as "superposition." This fundamental nature requires us to view the microscopic world through a lens of probability rather than certainty.
Because quantum mechanics governs the behavior of particles at microscopic scales, it also introduces certain limits and principles regarding measurement and observation, such as the Heisenberg Uncertainty Principle. This principle showcases the inherent uncertainty present in measuring particle properties, which becomes significant at the quantum level but often negligible in our macroscopic experiences.
Uncertainty in Position
The uncertainty in position is a key concept in quantum mechanics, rooted in the Heisenberg Uncertainty Principle. According to this principle, at a quantum scale, one cannot measure the exact position and momentum (or velocity) of a particle simultaneously with unlimited precision. The more precisely you know a particle's position, the less precisely you can know its momentum, and vice versa. In the context of the mosquito exercise, the uncertainty in position, denoted by \(Δx\), is related to the dimensions of the room. Here, \(Δx\) is set at the room's width, 5.0 m, since the mosquito can be flying anywhere horizontally from one wall to the other.
This concept is important because it sets a fundamental limit rather than one imposed by measurement devices. If the width of the room were smaller or larger, so would the potential area—in which the mosquito’s exact position could be uncertain—affecting calculations based on the Heisenberg principle.
Uncertainty in Velocity
Uncertainty in velocity is directly tied to uncertainty in momentum, given that momentum is the product of mass and velocity. This uncertainty is a central aspect of the Heisenberg Uncertainty Principle, with the formula \(Δx \, \cdot \, Δp \geq \frac{h}{4π}\). Here, \(Δp\) represents the uncertainty in momentum and is equivalent to \(m \, \cdot \, Δv\). Rearranging this equation helps us determine the uncertainty in velocity \(Δv\), which is crucial when trying to swat our flighty mosquito.
Even with a small mass like 1.5 mg, the uncertainty generated through the equation becomes insightful, although practically negligible when compared to everyday mosquito behavior. In our macroscopic world, such fine quantum details don't prevent us from achieving tasks like swatting a mosquito. Thus, while theoretically significant, the actual speed already expected from mosquitoes ensures the uncertainty poses no real hindrance in this scenario.

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Most popular questions from this chapter

A beam of alpha particles is incident on a target of lead. A particular alpha particle comes in "head-on" to a particular lead nucleus and stops \(6.50 \times 10^{-14} \mathrm{~m}\) away from the center of the nucleus. (This point is well outside the nucleus.) Assume that the lead nucleus, which has 82 protons, remains at rest. The mass of the alpha particle is \(6.64 \times 10^{-27} \mathrm{~kg} .\) (a) Calculate the electrostatic potential energy at the instant that the alpha particle stops. Express your result in joules and in \(\mathrm{MeV}\). (b) What initial kinetic energy (in joules and in MeV) did the alpha particle have? (c) What was the initial speed of the alpha particle?

Imagine another universe in which the value of Planck's constant is \(0.0663 \mathrm{~J} \cdot \mathrm{s},\) but in which the physical laws and all other physical constants are the same as in our universe. In this universe, two physics students are playing catch. They are \(12 \mathrm{~m}\) apart, and one throws a \(0.25 \mathrm{~kg}\) ball directly toward the other with a speed of \(6.0 \mathrm{~m} / \mathrm{s}\). (a) What is the uncertainty in the ball's horizontal momentum, in a direction perpendicular to that in which it is being thrown, if the student throwing the ball knows that it is located within a cube with volume \(125 \mathrm{~cm}^{3}\) at the time she throws it? (b) By what horizontal distance could the ball miss the second student?

Calculate the de Broglie wavelength of (a) a \(50.0 \mathrm{~kg}\) woman jogging leisurely at \(2.0 \mathrm{~m} / \mathrm{s},\) (b) a free electron with kinetic energy \(2.0 \mathrm{MeV}\). and (c) a free electron with kinetic energy \(20 \mathrm{eV}\). Use the proper relativistic expression when necessary.

A scientist has devised a new method of isolating individual particles. He claims that this method enables him to detect simultaneously the position of a particle along an axis with a standard deviation of \(0.12 \mathrm{nm}\) and its momentum component along this axis with a standard deviation of \(3.0 \times 10^{-25} \mathrm{~kg} \cdot \mathrm{m} / \mathrm{s}\). Use the Heisenberg uncertainty principle to evaluate the validity of this claim.

Suppose that the uncertainty of position of an electron is equal to the radius of the \(n=1\) Bohr orbit for hydrogen. Calculate the simultaneous minimum uncertainty of the corresponding momentum component, and compare this with the magnitude of the momentum of the electron in the \(n=1\) Bohr orbit. Discuss your results.

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