Concave mirror and virtual image

[jnimagine]

we used a concave mirror and a candle for an experiment
when the candle wa placed between the vertex and the focus of the mirror (f=12.7cm) a virtual image appeared behind the mirror.
We measure the image distance approximately by pointing a finger towards where the image might be and got 6.0cm (-6.0 when used in mirror equation) and the object was at 6.35cm. However, when I use the mirror equation to calculate the focus, i get a negative answer that is not even close to the actual focus 12.7cm. Do u think this is just due to human errors of not measuring the image distance accurately or is there some other factors that can account for this? OR is the image distance supposed to be almost the same as the object distance in this case?

 

[jtbell]

For the given focal length (12.7) and object distance (6.35), you should get an image distance of -12.7.

So you must have either put the object in the wrong location, or else measured the image distance incorrectly. It sounds like you used the "parallax method" to locate the image. That is, you moved your finger around until you found a location where it appeared to line up with the image no matter what angle you looked at them from. I find that many students have trouble with this at first.

 

[astrokreng]

It is likely that the difference in the measured image distance and the calculated focus is due to human error in measurement. The mirror equation is an idealized mathematical equation and does not take into account factors such as imperfections in the mirror or slight variations in the placement of the candle and finger. Additionally, in this experiment, the object distance is close to the focal length of the mirror, so the image distance should also be close to the object distance. However, it is normal for there to be slight variations in the measured values due to experimental limitations. It is important to repeat the experiment multiple times and take an average of the values to reduce the impact of human error.