Light - Reflection and Refraction: common misconceptions

If your child says… “The mirror image can land on paper.”

Ask together

Does the light actually meet behind the mirror, or only seem to?

What’s true

Reflected light only appears to come from behind the mirror, so its image is virtual.

If your child says… “The shiny side curves inward, so it is convex.”

Ask together

Does the shiny surface curve inward or bulge outward?

What’s true

Name the mirror from its reflecting side: concave curves inward, while convex bulges outward.

If your child says… “A concave mirror always gives an upside-down image.”

Ask together

Which image comes from actual ray crossings, and which comes from dashed extensions?

What’s true

An object between the pole and focus produces an upright, virtual image.

If your child says… “A convex mirror makes things bigger.”

Ask together

Which object is farther away, and which image is smaller?

What’s true

A convex mirror always gives an image smaller than the ordinary object in front of it.

If your child says… “I just add the two distances.”

Ask together

Would −30 cm give the reciprocal image distance we calculated?

What’s true

Use reciprocal distances with their signs; here, magnification is negative one, meaning equal height and inverted.

If your child says… “A higher refractive index means faster light.”

Ask together

When you divide the same number by something smaller, what happens to the answer?

What’s true

Dividing light’s vacuum speed by its speed in a material gives a number without units.

If your child says… “A convex lens spreads light out.”

Ask together

After the convex lens, does the parallel ray move towards the axis or away?

What’s true

A convex lens brings parallel light together, while a concave lens spreads it apart.

If your child says… “I divide by the focal length in centimetres.”

Ask together

Which unit must we use before dividing one by the focal length?

What’s true

Convert centimetres to metres before dividing, with convex power positive and concave power negative.