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Ch 37: The Foundations of Modern Physics
Knight Calc - Physics for Scientists and Engineers 5th Edition
Knight Calc5th EditionPhysics for Scientists and EngineersISBN: 9780137344796Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoKnight Calc 5th EditionCh 37: The Foundations of Modern PhysicsProblema 16a
Capitolo 37, Problema 16a

Express in eV (or keV or MeV if more appropriate): The kinetic energy of an electron moving with a speed of 5.0 x 10⁶ m/s .

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Step 1: Recall the formula for kinetic energy, which is given by \( KE = \frac{1}{2}mv^2 \), where \( m \) is the mass of the electron and \( v \) is its velocity.
Step 2: Substitute the known values into the formula. The mass of an electron \( m \) is approximately \( 9.11 \times 10^{-31} \; \text{kg} \), and the velocity \( v \) is given as \( 5.0 \times 10^6 \; \text{m/s} \).
Step 3: Calculate the kinetic energy in joules using the formula \( KE = \frac{1}{2}mv^2 \). This involves squaring the velocity, multiplying by the mass, and then dividing by 2.
Step 4: Convert the kinetic energy from joules to electronvolts (eV). Use the conversion factor \( 1 \; \text{eV} = 1.602 \times 10^{-19} \; \text{J} \). Divide the kinetic energy in joules by this factor to express it in eV.
Step 5: If the resulting value is very large or very small, express it in keV (\( 1 \; \text{keV} = 10^3 \; \text{eV} \)) or MeV (\( 1 \; \text{MeV} = 10^6 \; \text{eV} \)) for convenience.

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Kinetic Energy

Kinetic energy is the energy an object possesses due to its motion, calculated using the formula KE = 0.5 * m * v², where m is the mass and v is the velocity of the object. For an electron, this energy can be expressed in electronvolts (eV), a unit commonly used in particle physics to represent small energy values.
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Mass of an Electron

The mass of an electron is approximately 9.11 x 10⁻³¹ kg. This small mass is crucial for calculating the kinetic energy of the electron when it is moving at high speeds, as even small changes in velocity can result in significant changes in kinetic energy due to the squared term in the kinetic energy formula.
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Conversion to Electronvolts

Electronvolts (eV) are a unit of energy defined as the amount of kinetic energy gained by an electron when it is accelerated through an electric potential difference of one volt. To convert kinetic energy from joules to electronvolts, one can use the conversion factor 1 eV = 1.602 x 10⁻¹⁹ joules, allowing for easier interpretation of energy values in the context of atomic and subatomic processes.
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