Which statement correctly defines a joule?

Which statement correctly defines a joule?

• A. The rate of doing work per second.
• B. The amount of work done when a force of one newton moves an object one meter along the direction of the force.
• C. The energy stored by a magnetic field.
• D. The potential energy of a charged particle.

Answer: (B)

A joule is the unit of work and energy, defined as the product of force and the distance over which that force acts in the same direction. So if a force of one newton moves an object one meter along the force’s direction, the work done is 1 N × 1 m = 1 joule. This directly matches the definition of a joule. The other ideas describe related concepts but not the unit itself: the rate of doing work per second is a watt (power), magnetic energy is a form of energy stored in a magnetic field, and potential energy of a charged particle is another form of energy—measured in joules but not defining what a joule is.

A joule is the unit of work and energy, defined as the product of force and the distance over which that force acts in the same direction. So if a force of one newton moves an object one meter along the force’s direction, the work done is 1 N × 1 m = 1 joule. This directly matches the definition of a joule.

The other ideas describe related concepts but not the unit itself: the rate of doing work per second is a watt (power), magnetic energy is a form of energy stored in a magnetic field, and potential energy of a charged particle is another form of energy—measured in joules but not defining what a joule is.