Katla stands a paper arrow 20 cm in front of a convex mirror whose focal length is 10 cm. This mirror has no focal point in front of it at all. The rules still build the diagram.
This lesson constructs the convex case: the beams reflect off the bulging surface, and everything virtual happens behind the mirror.
The skeleton changes in one way: the focal point's dot sits behind the mirror now, because a convex mirror's focal point is virtual.
Ray 1 leaves the arrow's tip parallel, strikes the mirror, and reflects directly away from the virtual focal point.
Its dashed trace-back runs behind the mirror, straight through the virtual focal point on the principal axis.
Ray 2 is the center ray: from the tip to the point where the axis meets the mirror, reflecting at an equal angle.
In front of the mirror the two reflected rays spread apart and never cross.
Behind the mirror, their dashed trace-backs cross between the mirror and the virtual focal point.
The crossing sits on the tip's side of the axis and closer to the axis than the tip. So the image is drawn right side up and smaller than the arrow.
An arrow stands 15 cm from a convex mirror with a focal length of 6 cm. Plan the rays that locate the image of its tip.
Ray 1: from the tip, parallel to the principal axis; it reflects directly away from the virtual focal point, its dashed trace-back passing through that point.
Ray 2: from the tip to the point where the axis meets the mirror; it reflects at an equal angle.
The dashed trace-backs cross behind the mirror, between the mirror and the virtual focal point.
The image of the tip sits at that crossing.
Two rays, both traced back: the tip's image is at the dashed crossing behind the mirror.
Jorun finishes the diagram for an arrow 9 cm from a convex mirror with a focal length of 5 cm. Where does the image arrow sit, and how is it drawn?
Only the dashed trace-backs cross, so the image is virtual and sits behind the mirror.
The crossing lies between the mirror and the virtual focal point, on the tip's side of the axis.
The crossing sits closer to the axis than the tip, so the image is drawn smaller, right side up.
An upright, reduced image arrow behind the mirror, between the mirror and the virtual focal point.
In the convex construction, ray 1 leaves the arrow's tip parallel to the principal axis. Which describes its reflection?
The two reflected rays spread apart in front of the convex mirror. Where is the image of the tip found?
Jorun says: 'In the finished convex mirror diagram, the image arrow sits behind the mirror and is smaller than the object.' Is Jorun correct?
Lennart completes the ray diagram for an arrow 18 cm from a convex mirror with a focal length of 8 cm. Which description fits the correct finished diagram?
Why must the image in a convex mirror diagram be drawn behind the mirror?
A birthday balloon floats 30 cm from a convex mirror with a focal length of 12 cm. Katla completes the diagram. Which describes the drawn image?