Which statement gives the condition for an EMF to be induced in a conductor?
Selby watches a star whose light has traveled for years through empty space. Nothing carried the wave, and it kept going the whole way.
The last lesson said that electromagnetic waves need no medium. This lesson explains why.
Starlight crosses light-years of vacuum with nothing to carry it.
A mechanical wave could never do that: it needs a medium, and in a vacuum there is nothing to oscillate.
In magnetism you saw induction: when the magnetic field through a conductor changes, a voltage appears in the conductor.
The fields of an electromagnetic wave go one step further. They need no conductor and no material at all.
In empty space, a changing electric field creates a changing magnetic field.
And a changing magnetic field creates a changing electric field.
Each field creates the next a little farther along, and the wave carries itself forward.
In an electromagnetic wave crossing a vacuum, what creates the wave's changing magnetic field?
The wave carries a changing electric field.
A changing electric field creates a changing magnetic field.
The wave's own changing electric field creates it.
Light from a distant galaxy crosses millions of years of empty space. Explain why it never needs a material to keep going.
The wave's changing electric field creates a changing magnetic field.
That changing magnetic field creates a changing electric field.
Each field creates the next, so the wave regenerates itself as it travels.
The wave keeps itself going, so it needs no medium.
In an electromagnetic wave crossing empty space, what does the wave's changing electric field create?
Quenby says: 'Each changing field in an electromagnetic wave creates the other, so the wave keeps itself going.' Is Quenby correct?
Light from a distant star crosses empty space for years. What carries the wave along the way?
Why can an electromagnetic wave travel where there is no material at all?
Rurik remembers that induction needed a conductor. An electromagnetic wave crosses empty space with no conductor anywhere. Which statement is correct?
In an electromagnetic wave traveling through a vacuum, the magnetic field at one point is changing. What does that changing magnetic field create?