An object is what the rays of light have come from directly prior to striking the mirror. An image is the location from which the rays of light appear to be coming from. Object distance (u) is the distance between mirror and object. Image distance (v) is the distance between mirror and image.
Parallax is the relative movement of two objects due to the movement of the observer.
Note: The object is usually a pin or cross threads on a lamp box.
In practice, we are generally concerned with the parallax between an object (such as a search pin) and an image.
DEMONSTRATION 12.1
Demonstration of the No Parallax by Locating an Image in a Plane Mirror
Search pin
Virtual image in mirror
v
Observer Object pin
Plane mirror u Cardboard Fig 12.2
Apparatus Plane mirror, 2 pins, sheet of cardboard
Procedure Set up apparatus as illustrated in Fig 12.2. Position the search pin so that it is in line with the image (behind the mirror).
Move your head so that you are viewing the search pin and image from a different angle. If there is relative movement between them, they are not in the same location.
If the search pin appears to be moving faster than the image, move it back; if it moves slower bring it closer. Keep adjusting the search pin and viewing it and the image from different angles until there is no relative movement between them.
Observation A location is found where there is no parallax between the search pin and the image of the object pin.
Conclusion The search pin and the image are both at this location.
