Advertisements
Advertisements
प्रश्न
A concave mirror of focal length 12 cm forms three times the magnified virtual image of an object. Find the distance of the object from the mirror.
Advertisements
उत्तर
Given Data:
- Focal length (f) = −12 cm (Concave mirror → Focal length is negative)
- Magnification (m) = +3 (Virtual, magnified image → Positive magnification)
- Object distance (u) = ?
Use Magnification Formula
`m = -v/u`
`3 = -v/u`
v = −3u
`1/f = 1/v + 1/u`
Substituting f = −12 and v = −3u:
`1/-12 = 1/(-3u) + 1/u`
`1/-12 = (1+3)/(3u)`
`1/-12 = 4/(3u)`
−12 × 4 = 3u
−48 = 3u
u = −8 cm
The negative sign indicates that the object is placed in front of the mirror at a distance of 8 cm from the pole.
APPEARS IN
संबंधित प्रश्न
A man uses a concave mirror for shaving. He keeps his face at a distance of 25 cm from the mirror and gets an image which is 1.4 times enlarged. Find the focal length of the mirror.
A narrow pencil of parallel light is incident normally on a solid transparent sphere of radius r. What should be the refractive index is the pencil is to be focussed (a) at the surface of the sphere, (b) at the centre of the sphere.
A diverging lens of focal length 20 cm and a converging mirror of focal length 10 cm are placed coaxially at a separation of 5 cm. Where should an object be placed so that a real image is formed at the object itself?
A converging lens and a diverging mirror are placed at a separation of 15 cm. The focal length of the lens is 25 cm and that of the mirror is 40 cm. Where should a point source be placed between the lens and the mirror so that the light, after getting reflected by the mirror and then getting transmitted by the lens, comes out parallel to the principal axis?
How can the spherical aberration produced by a lens be minimized?
The focal length of a convex lens made of glass of refractive index (1.5) is 20 cm.
What will be its new focal length when placed in a medium of refractive index 1.25?
Is focal length positive or negative? What does it signify?
A spherical mirror is obtained as shown in the figure from a hollow glass sphere. if an object is positioned in front of the mirror, what will be the nature and magnification of the image of the object? (Figure drawn as schematic and not to scale)
Parallel rays striking a spherical mirror far from the optic axis are focussed at a different point than are rays near the axis thereby the focus moves toward the mirror as the parallel rays move toward the outer edge of the mirror. What value of incidence angle θ produces a 2% change in the location of the focus, compared to the location for θ very close to zero?
If an object is placed at a distance of 10 cm in front of a concave mirror of a focal length of 20 cm, the image formed will be ______.
Why does a car driver use a convex mirror as a rear-view mirror?
