Chapter 28: Problem 1
A proton traveling at \(23.0^{\circ}\) with respect to the direction of a magnetic field of strength \(2.60 \mathrm{mT}\) experiences a magnetic force of \(6.50 \times 10^{-17} \mathrm{~N}\). Calculate (a) the proton's speed and (b) its kinetic energy in electron-volts.
Short Answer
Expert verified
The proton's speed is approximately \(6.53 \times 10^6 \text{ m/s}\) and its kinetic energy is approximately \(2.24 \times 10^6 \text{ eV}\).
Step by step solution
01
Understanding the Magnetic Force Formula
The magnetic force experienced by a charged particle moving through a magnetic field can be calculated using the formula: \[ F = qvB\sin(\theta) \]where:- \( F \) is the magnetic force experienced by the particle,- \( q \) is the charge of the proton (\(1.6 \times 10^{-19} \text{ C}\)),- \( v \) is the speed of the proton,- \( B \) is the magnetic field strength here \(2.60 \text{ mT}\) (or \(2.60 \times 10^{-3} \text{ T}\)),- \( \theta \) is the angle between the velocity and the magnetic field direction.
02
Rearrange the Formula to Solve for Speed
We need to find the speed \( v \) of the proton. Rearrange the formula for \( v \):\[ v = \frac{F}{qB\sin(\theta)} \]
03
Substitute Known Values and Calculate Speed
Substitute \( F = 6.50 \times 10^{-17} \text{ N} \), \( q = 1.6 \times 10^{-19} \text{ C} \), \( B = 2.60 \times 10^{-3} \text{ T} \), and \( \theta = 23.0^{\circ} \):\[ v = \frac{6.50 \times 10^{-17}}{1.6 \times 10^{-19} \times 2.60 \times 10^{-3} \times \sin(23.0^{\circ})} \]Calculate:\[ \sin(23.0^{\circ}) \approx 0.3907 \]\[ v \approx \frac{6.50 \times 10^{-17}}{1.6 \times 10^{-19} \times 2.60 \times 10^{-3} \times 0.3907} \]\[ v \approx 6.53 \times 10^6 \text{ m/s} \]
04
Calculate Kinetic Energy in Joules
Kinetic energy \( KE \) is given by:\[ KE = \frac{1}{2}mv^2 \]where \( m \) is the mass of the proton \( (1.67 \times 10^{-27} \text{ kg}) \).\[ KE = \frac{1}{2} \times 1.67 \times 10^{-27} \times (6.53 \times 10^6)^2 \]Calculate:\[ KE \approx 3.58 \times 10^{-13} \text{ J} \]
05
Convert Kinetic Energy to Electron-Volts
To convert the kinetic energy from joules to electron-volts (eV), use the conversion:1 eV = \( 1.6 \times 10^{-19} \text{ J} \).\[ KE \approx \frac{3.58 \times 10^{-13}}{1.6 \times 10^{-19}} \]\[ KE \approx 2.24 \times 10^6 \text{ eV} \]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Proton Speed
The speed of a proton is a critical concept when dealing with problems that involve magnetic fields and forces. Knowing the speed helps us understand how a proton navigates through a magnetic field. In this scenario, the proton travels at an angle of \(23.0^{\circ}\) to the magnetic field. The formula used to determine the proton's speed originates from the magnetic force equation:\[ F = qvB \sin(\theta) \]Here:- \( F \) is the magnetic force (\(6.50 \times 10^{-17} \text{ N}\)).- \( q \) is the charge of the proton, approximately \(1.6 \times 10^{-19} \text{ C}\).- \( B \) is the magnetic field's strength (\(2.60 \text{ mT} = 2.60 \times 10^{-3} \text{ T}\)).- \( \theta \) is the angle (\(23.0^{\circ}\) in this case).To find the speed \( v \), we rearrange the equation:\[ v = \frac{F}{qB \sin(\theta)} \]Plugging in the known values and calculating the speed yields \( v \approx 6.53 \times 10^6 \text{ m/s} \). That means the proton is moving incredibly fast, showcasing how subatomic particles can travel at high speeds when influenced by a magnetic field.
Kinetic Energy
Kinetic energy (KE) represents the energy that a particle possesses because of its motion. For the proton in question, its kinetic energy is directly related to its speed. The formula for kinetic energy is:\[ KE = \frac{1}{2} mv^2 \]Where:- \( m \) is the mass of the proton, approximately \(1.67 \times 10^{-27} \text{ kg}\).- \( v \) is the speed of the proton (\(6.53 \times 10^6 \text{ m/s}\)).Substituting these values into the kinetic energy equation gives:\[ KE = \frac{1}{2} \times 1.67 \times 10^{-27} \times (6.53 \times 10^6)^2 \]After performing the calculation, we find that \( KE \approx 3.58 \times 10^{-13} \text{ J}\). This amount of kinetic energy may seem small, but given the proton's tiny mass, it reveals that even light particles can have significant energy due to their high speeds.
Electron-Volts
An electron-volt (eV) is a convenient unit for measuring energy on the scale of subatomic particles. One electron-volt is the amount of kinetic energy gained by a single electron when it is accelerated through an electric potential difference of one volt. This conversion is useful because it allows us to express particle energy in a more intuitive way than using joules.In our calculation, the proton's kinetic energy in joules \( (3.58 \times 10^{-13} \text{ J}) \) must be converted to electron-volts. The conversion factor is:1 eV = \( 1.6 \times 10^{-19} \text{ J} \).To convert, simply divide the kinetic energy in joules by this conversion factor:\[ KE \approx \frac{3.58 \times 10^{-13}}{1.6 \times 10^{-19}} \]Which results in approximately \( 2.24 \times 10^6 \text{ eV} \). Expressing kinetic energy in electron-volts provides a clearer understanding of the energy scales involved in subatomic physics.