Question Video: Rotating an Object in Front of a Mirror Science

Light from an object is reflected by a plane mirror. The shaded side of the object is marked with a symbol. The mirror produces an image of the object, as shown in the following figure. Which of the following figures correctly shows the object if it is rotated so that the shaded side of it faces away from the mirror? The base of the object remains in contact with the surface that it initially rests on while the object is rotated. [A] Figure A [B] Figure B

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Video Transcript

Light from an object is reflected by a plane mirror. The shaded side of the object is marked with a symbol. The mirror produces an image of the object, as shown in the following figure. Which of the following figures correctly shows the object if it is rotated so that the shaded side of it faces away from the mirror? The base of the object remains in contact with the surface that it initially rests on while the object is rotated. Is it option (A) or option (B)?

This question is asking if images seen in a mirror are reversed. It is sometimes said that an image in a mirror is the reverse of an object that is in front of the mirror.

To see if this is correct, let’s consider some light rays from an object in front of a plane mirror that reflect from the mirror. In this sketch, the object and image are both aligned parallel to the mirror. Notice that the top of the object and the top of the image can be connected by a line that is at 90 degrees to the mirror. The same thing is true for the bottoms of the object and image.

Let’s say that now we rotate the object around its center so the top and bottom are reversed. If we were observing the object from behind, we would see a color reversal as the object goes through its rotation. In the same way, when the object in the original diagram is rotated, the symbol on it will be reversed. Therefore, the symbol will not look like the symbol in option (B), which has not been reversed, but rather it will look like the symbol in option (A), which is reversed.

For our answer then we choose option (A). This is how the object would appear if it is rotated so its shaded side faces away from the mirror.

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