Wave Optics: common misconceptions

If your child says… “Light travels along the wavefront.”

Ask together

Does the propagation arrow run along the old wavefront or across it?

What’s true

In a medium identical in every direction, light travels perpendicular to its wavefront.

If your child says… “Slower light must vibrate less often.”

Ask together

Which sets the vibration rate: the incoming light or its speed inside glass?

What’s true

The incoming light sets the frequency, so slower travel means a shorter wavelength.

If your child says… “Same colour means steady bands.”

Ask together

Which wave pair keeps the same gap between corresponding crests?

What’s true

Random changes in relative phase make interference bands average out.

If your child says… “Half a wavelength gives half the maximum brightness.”

Ask together

What remains when equal opposite amplitudes add?

What’s true

Equal beams starting in phase cancel at a half-wavelength path difference when their polarisations match.

If your child says… “Different colours meet at the same fringe number.”

Ask together

How many gaps does each row cross before its marks first line up again?

What’s true

Different wavelengths need different nonzero orders to reach a shared bright position.

If your child says… “Delaying one beam changes the gaps.”

Ask together

In the shifted row, which gaps changed?

What’s true

A constant added phase shifts every fringe equally.

If your child says… “A wider slit spreads light more.”

Ask together

Would bringing the first dark boundaries closer make the central bright region wider or narrower?

What’s true

Narrowing the slit moves its first dark boundaries farther from the bright centre.

If your child says… “Half the field means half the intensity.”

Ask together

What happens to a half when you square it?

What’s true

Halving the electric-field amplitude leaves one quarter of the intensity.