Question
In parallax method for the determination of focal length of a concave mirror, the object should always be placed :
The correct answer is
between the pole(P) and the focus(F) of the concave mirror ONLY
Parallax Method: Object Placement for Concave Mirror Focal Length
To determine the focal length ($f$) of a concave mirror using the parallax method, the object must be positioned correctly relative to the mirror's optical points.
Required Object Position
- The object should be placed between the pole ($P$) and the principal focus ($F$) of the concave mirror.
Principle of Parallax Method
This specific placement ($P < \text{object distance} < F$) is crucial because it generates a virtual, erect, and magnified image behind the mirror.
The parallax method relies on aligning the object with this virtual image. Precise alignment is achieved by observing the lack of relative movement (parallax) between the object and its image against a distant background. This allows for accurate measurement needed to calculate the focal length ($f$).
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