Student Exploration: Ray Tracing (Mirrors)
Vocabulary: concave mirror, convex mirror, focal point, magnification, real image,
reflect, virtual image
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
For th
...
Student Exploration: Ray Tracing (Mirrors)
Vocabulary: concave mirror, convex mirror, focal point, magnification, real image,
reflect, virtual image
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
For these questions, it would be helpful to have a metal spoon on hand. If you don’t
have one, try to imagine looking at yourself in a spoon.
1. Look at yourself in the front of the spoon (the side where the food sits). What do you
see?
I’m upside down.
The front of a spoon is an example of a concave mirror.
2. What do you see when you look at yourself in the back of a spoon? I am right side
up.
The back of a spoon is an example of a convex mirror.
Gizmo Warm-up
The Ray Tracing (Mirrors) Gizmo shows a side
view of a light bulb positioned to the left of a mirror.
Light rays passing from the light bulb to the mirror
are shown.
To begin, select the Concave mirror. Turn on
Colorize lines. Under Show lines, turn off the
Central line and the Line through focal point so
that only the Parallel line is showing.
1. The blue dot in front of the mirror is the focal point of the mirror. Move the light bulb
on the left around. What is always true about the ray that is reflected from the
parallel ray?
Whether the light source is closer or not, the light paths stay the same.
2. Turn off the Parallel line and turn on the Line through focal point. Move the light
bulb around. What do you notice about the reflected ray in this situation? The angle
changes as the height of the light source changes
Activity A:
Real and virtual
images
Get the Gizmo ready:
Check that the Concave mirror is selected.
Turn on the Parallel line, Central line, and
Line through focal point.
Place the light bulb above -24 on the central
axis, with the focal point at -12.
Introduction: A concave mirror is also called a “converging mirror” because it reflects
light rays into a point. A real image is formed where the reflected light rays converge at
a point. Unlike a virtual image that forms behind a mirror, a real image can be
projected onto a screen.
Question: How do mirrors create real and virtual images?
1. Observe: In its current configuration, the distance from the light bulb to the focal
point is slightly more than 12 units. The distance from the focal point to the mirror is
exactly 12 units.
A. What do you notice about the size of the light bulb’s image? it is only one line
B. What do you notice about the orientation of the light bulb’s image?
It’s converged into one line, same as the apparent image.
2. Investigate: Complete each action described in the table below, and state how that
action affects the image.
Action Effect on image
Move the light bulb to the left. The reflection gets smaller
Move the light bulb to the right. The reflection gets bigger
Move the focal point to the left. Reflection gets bigger and further away
Move the focal point to the right. Reflection gets smaller and closer to the mirror
3. Analyze: Examine the results recorded in your table.
A. In general, how do the size and position of the image change when the
distance between the light bulb and the focal point increases?
The reflection would get smaller along with getting closer towards the mirror
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