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प्रश्न
At what distance from a concave mirror of focal length 10 cm should an object be placed so that:
its real image is formed 20 cm from the mirror?
उत्तर
Given
It is a concave mirror.
f=-10 cm
v=-20 cm
Since the image is real and forms in front of the mirror, the equation will be `1/f=1/v+1/u`
`1/-10=1/-20+1/u`
`2/u=1/-10+1/20`
`1/u=(-20+10)/200`
`1/u = (-10)/200`
`1/u=-1/20`
u=-20 cm
Therefore, the object should be placed at a distance of 20 cm from the mirror to form a real image.
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संबंधित प्रश्न
In the concave reflector of a torch, the bulb is placed:
(a) between the pole and focus of reflector
(b) at the focus of reflector
(c) between focus and centre of curvature of reflector
(d) at the centre of curvature of reflector
A concave mirror has a focal length of 25 cm. At which of the following distance should a person hold his face from this concave mirror so that it may act as a shaving mirror?
(a) 45 cm
(b) 20 cm
(c) 25 cm
(d) 30 cm
Give reason for your choice.
According to New Cartesian Sign Convention:
(a) focal length of concave mirror is positive and that of convex mirror is negative
(b) focal length of both concave and convex mirrors is positive
(c) focal length of both concave and convex mirrors is negative
(d) focal length of concave mirror is negative and that of convex mirror is positive
One of the following does not apply to a concave mirror this is:
(a) focal length is negative
(b) image distance can be positive or negative
(c) image distance is always positive
(d) height of image can be positive or negative
An object is placed at a large distance in front of a concave mirror of radius of curvature 40 cm. The image will be formed in front of the mirror at a distance:
(a) 20 cm
(b) 30 cm
(c) 40 cm
(d) 50 cm
A concave mirror cannot be used as:
(a) a magnifying mirror
(b) a torch reflector
(c) a dentist's mirror
(d) a real view mirror
Match the following.
| Convex mirror | Radio telescopes |
| Parobolic mirror | Rear – view mirror |
| Snell’s law | Kaleidoscope |
| Dispersion of light | sin i/sin r =μ |
| Refractive index | Rainbow |
The radius of curvature of a concave mirror whose focal length is 5cm is ______
Under which of the following conditions a concave mirror can form an image larger than the actual object?
In which of the following, the image of an object placed at infinity will be highly diminished and point sized?
