Chapter 25: Problem 31
A proton \(\left(q=e, m_{p}=1.67 \times 10^{-27} \mathrm{~kg}\right)\) is accelerated from rest through a potential difference of \(1.0 \mathrm{MV}\). What is its final speed?
Short Answer
Expert verified
The final speed of the proton is approximately \(1.38 \times 10^7\) m/s.
Step by step solution
01
Calculate the energy gained by the proton
When a proton is accelerated through a potential difference, it gains kinetic energy equal to the electric potential energy. The energy gained is given by the formula: \[E = qV\] where \(q\) is the charge of the proton, \(e = 1.6 \times 10^{-19} \text{ C}\), and \(V = 1.0 \text{ MV} = 1.0 \times 10^6 \text{ V}\). Thus, \[E = 1.6 \times 10^{-19} \text{ C} \times 1.0 \times 10^6 \text{ V} = 1.6 \times 10^{-13} \text{ J}\].
02
Relate kinetic energy to velocity
The kinetic energy gained by the proton can be related to its velocity (\(v\)) using the kinetic energy formula: \[E = \frac{1}{2} m v^2\] where \(m\) is the mass of the proton, \(m_p = 1.67 \times 10^{-27} \text{ kg}\).
03
Solve for velocity
Set the expressions for kinetic energy equal to solve for \(v\): \[\frac{1}{2} m v^2 = 1.6 \times 10^{-13} \text{ J}\]. Rearranging gives: \[v^2 = \frac{2E}{m} = \frac{2 \times 1.6 \times 10^{-13}}{1.67 \times 10^{-27}}\]. Calculate \(v^2 \): \[v^2 = \frac{3.2 \times 10^{-13}}{1.67 \times 10^{-27}} \approx 1.917 \times 10^{14} \].
04
Calculate final speed
Take the square root of the result to find \(v\): \[v = \sqrt{1.917 \times 10^{14}} \approx 1.38 \times 10^7 \text{ m/s}\].
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Proton Acceleration
Proton acceleration occurs when a proton (\(q = e, \ m_p = 1.67 \times 10^{-27}\text{kg}\)) is subjected to an electric field, gaining speed and kinetic energy. When we apply a potential difference to a proton, the force exerted by the electric field accelerates the proton from rest. This force changes the proton's speed by converting potential energy into kinetic energy. The equation \(F = qE\) cannot be ignored, but for potential difference calculations, we focus on energy transformations.
- Acceleration means an increase in velocity over time.
- An electric field causes the proton to accelerate.
- Force is a product of charge and electric field \(F = qE\).
Potential Difference
The concept of potential difference, often referred to as voltage, is crucial in understanding how protons are accelerated. A potential difference, measured in volts (V), represents the work done per unit charge to move a charge between two points.
When a proton is accelerated by a potential difference, it gains energy. For a potential difference \(V\) of \(1.0 \text{ MV} = 1.0 \times 10^6 \text{ V}\), the proton gains energy equal to its charge \(q\) multiplied by the potential difference \(V\): \(E = qV\). For a proton, \(q = 1.6 \times 10^{-19}\text{C}\), so the energy gained is given by:
\[E = 1.6 \times 10^{-19} \text{ C} \times 1.0 \times 10^6 \text{ V} = 1.6 \times 10^{-13} \text{ J}\]
When a proton is accelerated by a potential difference, it gains energy. For a potential difference \(V\) of \(1.0 \text{ MV} = 1.0 \times 10^6 \text{ V}\), the proton gains energy equal to its charge \(q\) multiplied by the potential difference \(V\): \(E = qV\). For a proton, \(q = 1.6 \times 10^{-19}\text{C}\), so the energy gained is given by:
\[E = 1.6 \times 10^{-19} \text{ C} \times 1.0 \times 10^6 \text{ V} = 1.6 \times 10^{-13} \text{ J}\]
- Potential difference is measured in volts (V).
- 1 MV equals \(1.0 \times 10^6\) volts.
- The proton gains energy when crossing this potential difference.
Kinetic Energy Calculation
Kinetic energy is the energy of motion. When a proton is accelerated through a potential difference, its electric potential energy converts into kinetic energy. Kinetic energy (KE) is calculated using the formula,\(KE = \frac{1}{2} mv^2\), where \(m\) is the mass of the proton. Substituting in the provided data,
- Mass of proton, \(m_p = 1.67 \times 10^{-27}\text{ kg}\)
- Kinetic energy gained \(E = 1.6 \times 10^{-13}\text{ J}\)
Velocity Determination
To determine the velocity of a proton after acceleration, we use the calculated kinetic energy. Start with the formula\[\frac{1}{2} m v^2 = 1.6 \times 10^{-13} \text{ J}\].Rearranging the formula for \(v^2\):\[v^2 = \frac{2 \times 1.6 \times 10^{-13} \text{ J}}{1.67 \times 10^{-27} \text{ kg}}\],we find that\(v^2 = \frac{3.2 \times 10^{-13}}{1.67 \times 10^{-27}} \approx 1.917 \times 10^{14} \). To find the velocity \(v\), take the square root:\[v = \sqrt{1.917 \times 10^{14}} \approx 1.38 \times 10^7 \text{ m/s}\].This result shows the velocity of a proton after being accelerated by a potential difference of 1.0 MV. The relationship between the potential difference, energy, and velocity clearly illustrates the conversion of potential to kinetic energy in an easily measurable velocity.