Magnification is a dimensionless quantity; therefore, it has no SI unit.
Magnification is defined as the ratio of the image size to the object size. Since both measurements are lengths, the units cancel out, resulting in a unitless value. It's essentially a scaling factor.
Explanation
Magnification describes how much larger or smaller an image appears compared to the actual object. This is calculated as:
Magnification = (Image Size) / (Object Size)
Both image size and object size are typically measured in units of length, such as meters (m), centimeters (cm), or millimeters (mm). When you divide one length by another, the units cancel out, leaving a pure number.
Types of Magnification
While the core concept of magnification is unitless, it's important to note different types:
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Linear Magnification: This is the most common type, referring to the ratio of the image height to the object height. As explained above, it's unitless.
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Angular Magnification: This type relates to the angle subtended by an object when viewed through an optical instrument compared to the angle subtended by the same object when viewed with the naked eye. While it deals with angles, the magnification value itself is still typically expressed as a dimensionless ratio.
Example
If an object is 1 cm tall and its image is 5 cm tall, the magnification is 5. There are no units associated with this value. It simply means the image is 5 times larger than the object.
Conclusion
Magnification, representing the ratio of image size to object size, is a dimensionless quantity and thus has no associated SI unit.
