A concave mirror forms real images with magnifications -4 and -6 at two object positions. If the corresponding image positions differ by 30 cm, the focal length magnitude is:
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A concave mirror forms real images with magnifications −4 and −6 at two object positions. If the corresponding image positions differ by 30 cm, the focal length magnitude is:

G1 Physics · Accepted Answer

For real image M, v=f(M+1). Thus v₁=5f and v₂=7f. Difference=2f=30, so f=15 cm.