An object is placed at a distance of 30 cm in front of a concave mirror of focal length 15 cm. What are the position, nature, and magnification of the image formed?
Answer and explanation
Correct answer: B. Image formed at 30 cm in front of the mirror (at center of curvature), real, inverted, with magnification m = -1
.
- Step 1: For a concave mirror, by Cartesian sign convention: and .
- Step 2: The mirror formula is: .
- Step 3: Substitute values:
- Step 4: The image is formed at in front of the mirror (at ).
- Step 5: Magnification is .
- Step 6: The negative sign indicates a real and inverted image of the exact same size as the object.
Answer
Image formed at 30 cm in front of the mirror (at center of curvature), real, inverted, with magnification m = -1
Why not the others: 'Image at 10 cm behind mirror' confuses mirror sign conventions or uses a convex mirror formula; 'Image at 15 cm' places the image at the focal point (which only occurs when object is at infinity); 'Image at infinity' occurs when the object is at the principal focus ().
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