Electron Volts and Kinetic Energy

The lecture introduces the electron volt as a unit of energy suitable for subatomic particles, contrasting it with joules. It explains how to calculate energy in electron volts and convert it to joules. Two examples are provided: one calculating the potential difference needed for a helium nucleus to gain kinetic energy, and another determining the velocity of an electron with a given kinetic energy.

Why is the electron volt used instead of joules when dealing with subatomic particles?

• Because joules are too large for microscopic energy levels.

• Because joules are not a standard unit of energy.

• Because electron volts are easier to calculate.

• Because electron volts are a larger unit of energy.

What is the definition of one electron volt?

• The energy gained by an electron moving through a potential difference of one joule.

• The energy gained by a proton moving through a potential difference of one volt.

• The energy gained by an electron moving through a potential difference of one volt.

• The energy lost by an electron moving through a potential difference of one volt.

How many joules are equivalent to one electron volt?

• 1.6 x 10^-19 joules

• 1.6 x 10^19 joules

• 1.6 x 10^-9 joules

• 1.6 x 10^9 joules

What is the first step in calculating the potential difference for a helium nucleus to gain kinetic energy?

• Convert joules to electron volts.

• Convert electron volts to joules.

• Calculate the charge of the helium nucleus.

• Determine the mass of the helium nucleus.

What is the charge of the helium nucleus used in the example?

• 2.4 x 10^-14 coulombs

• 3.1 x 10^-19 coulombs

• 7.7 x 10^4 coulombs

• 1.6 x 10^-19 coulombs

Why is the calculated potential difference negative in the helium nucleus example?

• Because the nucleus loses kinetic energy.

• Because the nucleus moves from higher to lower potential.

• Because the nucleus moves from lower to higher potential.

• Because the nucleus gains potential energy.

What is the first step in calculating the velocity of an electron given its kinetic energy?

• Convert the kinetic energy from joules to electron volts.

• Determine the charge of the electron.

• Convert the kinetic energy from electron volts to joules.

• Calculate the mass of the electron.

What is the mass of the electron used in the velocity calculation example?

• 2.7 x 10^7 kilograms

• 3.2 x 10^-16 kilograms

• 1.6 x 10^-19 kilograms

• 9.11 x 10^-31 kilograms

What is the final velocity of the electron calculated in the example?

• 2.7 x 10^7 meters per second

• 3.2 x 10^16 meters per second

• 9.11 x 10^-31 meters per second

• 1.6 x 10^-19 meters per second

Why does the negative sign disappear in the velocity calculation of the electron?

• Because the electron gains kinetic energy.

• Because the electron loses potential energy.

• Because the electron gains potential energy.

• Because the electron loses kinetic energy.