Question

Which of the statements concerning light are true? The speed of light is the same no matter what material it is traveling through. Its propagation direction is parallel to both the electric field and the magnetic field. The speed of light in matter is greater than the speed of light in a vacuum. Its propagation direction is perpendicular to both the electric field and the magnetic field. It moves at a constant speed through a vacuum. The speed of light in matter is less than the speed of light in a vacuum.

Answer 1

Answer:

The statements that are true concerning light are the last three statements:

• Its propagation direction is perpendicular to both the electric field and the magnetic field.

• It moves at a constant speed through a vacuum.

• The speed of light in matter is less than the speed of light in a vacuum.

Explanation:

Light is electromagnetic waves.  

The properties of the electromagnetic waves were established by James Clerk Maxwell.

They included that they are the result of the oscillation of a magnetic field in phase with an electric field which are always is always perpendicular to each other.

Also, the electromagnetic waves propagate at right-angles to the direction of both the magnetic and the electric field,  meaning that they are a type of transverse wave.

Thus, the second statement ("Its propagation direction is parallel to both the electric field and the magnetic field") is false, and the fourth statement ("Its propagation direction is perpendicular to both the electric field and the magnetic field") is true.

On the other hand, it is a postulate of the special theory of relativity that the speed of light is a constant (absolute value) in vacuum: nothing can travel faster than what light travels in vacuum. Thus, the fifth statement, "It moves at a constant speed through a vacuum" is true.

About the speed of light in matter, it is always less than the speed of light in vacuum. Thus, the first statement, "the speed of light is the same no matter what material it is traveling through", and the third statement "the speed of light in matter is greater than the speed of light in a vacuum" are false; while the last statement, "the speed of light in matter is less than the speed of light in a vacuum" is true.

The explanation on why the speed of light is less in a medium than in vacuum is related with the fact that at nanoscopic level the waves suffer polarization which means deviations from the straighi path, which makes that the net straight propagation is slower.