Electromagnetic Waves: common misconceptions

If your child says… “The wire and gap currents add together.”

Ask together

Are we counting the same charging twice?

What’s true

For this loop, choose a surface through the wire or through the gap. Each gives current i. Do not add results from different surfaces.

If your child says… “Any moving charge gives off waves.”

Ask together

Does moving straight at steady speed change a charge’s speed or direction?

What’s true

Charges radiate when their velocity changes, including changes of direction.

If your child says… “I find the travel direction using B × E.”

Ask together

Curl your right-hand fingers from the electric towards the magnetic field. Where does your thumb point?

What’s true

Reversing the order reverses the predicted direction; reversing both fields leaves travel unchanged.

If your child says… “I multiply electric amplitude by light’s speed to find magnetic amplitude.”

Ask together

Which operation isolates magnetic amplitude in the last line?

What’s true

In vacuum, magnetic amplitude equals electric amplitude divided by light’s speed.

If your child says… “Doubling the field strength doubles the intensity.”

Ask together

When a quantity is squared, does doubling it give twice or four times the result?

What’s true

A vacuum plane wave shares energy equally between its fields, and doubling amplitude quadruples intensity.

If your child says… “Longer wavelengths mean more energy.”

Ask together

Which side shows longer wavelengths, and which side gives each photon more energy?

What’s true

Longer wavelengths mean less photon energy.

If your child says… “Longer wavelengths make a narrower radar beam.”

Ask together

If longer wavelengths spread more, which wavelengths would help this dish select a narrower direction?

What’s true

For the same antenna width, beam spreading grows with wavelength.

If your child says… “Nuclei make X-rays; electrons make gamma rays.”

Ask together

Which panel shows a nuclear process?

What’s true

Their wavelengths overlap, but their sources differ.