Alabama Science in Motion Optics: Locating an Image in a Plane Mirror
Pre-lab Questions:
Answer the following pre-lab questions in your student response section before continuing.
1.
How can you tell where an object is when you look into a mirror?
2.
Materials/Equipment:
Equipment Qty Equipment Qty
Copy paper
Cardboard
1
1-2
Plane mirror
Mirror support
1
2
1 Pins 5
Procedure:
Note: Refer to the photo below as needed when placing the pins.
ruler
1.
Lay the sheet of copier paper on top of a couple of pieces of corrugated cardboard. (You need to be able to push pins through the cardboard. Sometimes two pieces of cardboard work better than just one.)
2.
Using your ruler, draw a line that divides the paper into 2 equal sections. This is the
“mirror” line. Using two mirror supports, place your mirror so that its front edge is along the line.

Alabama Science in Motion Optics: Locating an Image in a Plane Mirror
3.
Locate the center of the mirror and insert a pin into the paper 5 cm from the mirror. Draw a circle around the pin and label it “object.”
4.
Looking from the left front corner of the paper, close one eye and sight toward the pin image in the mirror. Take another pin and line it up vertically with the image in the mirror at around 5 cm from the mirror. Insert the pin when the pin and the image in the mirror appear to be one. Draw a circle around the pin and label it “1.”
5.
Using another pin, sight with one eye and line this pin up with the “1” pin and the image in the mirror. Insert it 5 cm away from the “1” pin (towards you). Draw a circle around the pin and label it with a “1” also.
These two pins should now form a straight line pointed at the image of your object pin you saw in the mirror!
6.
Now we are going to repeat the procedure from the right side. Looking from the right front corner of the paper, repeat the sighting procedure as described in steps 5 and 6 and place 2 pins on the right side at the same distances. Again, try to make both inserted pins line up with the object image in the mirror. Draw a circle around each pin and label each “2.”
7.
Remove the mirror, book, and pins. Take the ruler, line up the two “1” circles on the left, and draw a straight line extending behind the “mirror” line. This is the “1” line.
8.
Line up the two “2” circles and draw a straight line extending behind the “mirror” line until it intersects with the “1” line. This is the “2” line.
9.
The intersection of the 2 lines behind the “mirror” line represents the position for the virtual image of the “object” pin that was placed in front of the mirror. Measure the distance in centimeters from the “object” circle to the “mirror” line and measure the distance from the virtual image (where the “1” and “2” lines intersect) to the “mirror” line.
Theoretically, they should be the same distance. This illustrates why a person’s image in a mirror always seems to be at the same distance behind the mirror as the person is in front of the mirror.
Data:
Distance from object pin to mirror (Object distance): ________________ cm
Distance from intersection of lines 1 and 2 to mirror (Image distance) ____________cm
Questions:
1.
Were your object distance and image distances the same?
2.
Look closely at your mirror – which surface is reflective – the front or the back of the mirror? How could this affect your results?
3.
What conclusion did you make about the distance an object is in front of a plane mirror as compared to the image distance behind the mirror?