Question

In the early 1900s, it was proposed that the law of conservation of mass should be simultaneously considered with the law of conservation of energy to explain particular phenomena. Thus, a theory of conservation of mass-energy was proposed. Which of the following reasons could provide evidence to support the proposed theory?
A. After charged particles travel a complete loop around a circuit, the electric potential energy of the charged particles does not change, but the number of available charged particles that can move through the circuit is reduced. This is because charged particles are used in order for circuit elements to operate correctly.
B. After a photon of light is absorbed by certain metals, electrons are found to be ejected from the metals. This is because the energy contained in the massless photon is used to eject an electron with mass out of the metal.
C. After particles of a hot gas collide with other particles in the gas, the initial combined mass of all particles of the gas immediately before the collisions occur is not equal to the final combined mass of all particles immediately after the collisions. This is because some of the particles in the gas are destroyed in the collisions.
D. After the decay of certain unstable nuclei, the initial mechanical energy of an unstable nucleus is not equal to the final mechanical energy of the resultant particles immediately after the decay process. This is because some of the available mechanical energy is converted into a particle that was originally not accounted for.

Answer 1

Answer:

B. After a photon of light is absorbed by certain metals, electrons are found to be ejected from the metals. This is because the energy contained in the massless photon is used to eject an electron with mass out of the metal.

Explanation:

Before, in the early days, it was proposed to form a combined theory by joining the theory of conservation of mass and the theory of conservation of energy and form a combined theory of conservation of mass-energy. It was done to explain a particular theory of $\text{photoelectric effect}$.

The $\text{photoelectric effect}$ is the emission of the electrons form the surface of a metal when light energy strikes on it. Here, in this phenomenon, both mass and energy is conserved.

When the light strikes a metal surface, electrons gets ejected from the surface. The energy of the photon is used to eject the electron form the metal surface.