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प्रश्न
An object is placed (a) 20 cm, (b) 4 cm, in front of a concave mirror of focal length 12 cm. Find the nature and position of the image formed in each case.
उत्तर
Case (a)
Distance of the object from the mirror (u) = -20 cm
The focal length of the concave mirror (f) = -12 cm
We have to find the distance of the image (v).
Using the magnification formula, we get
`1/f=1/v+1/u`
so
`or 1/-12=1/v+1/-20`
`1/-12=1/v-1/20`
`or 1/20-1/12=1/v`
`or(3-5)/60=1/v`
`or -2/60=1/v`
`or v= 60/-2`
`v=-30` cm
The image will be at a distace of 30 cm in front of mirror.Again,
Magnification `(m)=(-v)/u `
`m=-(-30)/-20=-1.5`
Therefore, the image will be real, inverted and enlarged.
Thus the image is real, inverted and enlarged.
Case B
Distance of the object from the mirror (u) = -4 cm
The focal length of the concave mirror (f) = -12 cm
We have to find the distance of the image (v).
Using the mirror formula, we get
`1/f=1/v+1/u`
`1/-12=1/v+1/-4`
`or 1/4-1/12=1/v`
`or(3-1)/12=1/v`
`or 2/12=1/v`
Therefore, distance of image (v) is 6 cm.Now, using the magnification formula, we get
`m=-v/u`
`m=-6/-4=1.5`
Thus, the image is virtual and erect.
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संबंधित प्रश्न
A spherical mirror produces an image of magnification -1 on a screen placed at a distance of 50 cm from the mirror.
(a) Write the type of mirror.
(b) Find the distance of the image from the object.
(c) What is the focal length of the mirror?
(d) Draw the ray diagram to show the image formation in this case.
A student was asked by his teacher to find the image distance for various object distance in case of a given convex lens. He performed the experiment with all precautions and noted down his observations in the following table:
| S. No. |
Object distance (cm) |
Image distance (cm) |
| 1 | 60 | 15 |
| 2 | 48 | 16 |
| 3 | 36 | 21 |
| 4 | 24 | 24 |
| 5 | 18 | 36 |
| 6 | 16 | 48 |
After checking the observations table the teacher pointed out that there is a mistake in recording the image distance in one of the observations. Find the serial number of the observations having faulty image distance.
(A) 2
(B) 3
(C) 5
(D) 6
What is the difference between a real image and a virtual image? Give one example of each type of image
Linear magnification produced by a concave mirror may be:
(a) less than 1 or equal to 1
(b) more than 1 or equal than 1
(c) less than 1, more than 1 or equal to 1
(d) less than 1 or more than 1
A concave mirror produces magnification of +4. The object is placed:
(a) at the focus
(b) between focus and centre of curvature
(c) between focus and pole
(d) between the centre of curvature
Linear magnification (m) produced by a rear view mirror fitted in vehicles:
(a) is equal to one
(b) is less than one
(c) is more than one
(d) can be more less than one depending on the position of object
Explain what is meant by a virtual, magnified image.
An object of height 6 cm is placed perpendicular to the principal axis of a concave lens of focal length 5 cm. Use lens formula to determine the position, size and nature of the image if the distance of the object from the lens is 10 cm.
Give scientific reason.
Simple microscope is used for watch repairs.
In a reading glass what is the position of the object with respect to the convex lens used?
