We wish to obtain an erect image of an object, using a concave mirror of focal length 15 cm. What should be the range of distance of the object from the mirror? What is the nature of the image? Is the image larger or smaller than the object? Draw a ray diagram to show the image formation in this case.
Answer: When object is between principal focus and pole of a concave mirror, an erect, enlarged and virtual image is formed. So, we need to keep the object at a distance which is less than 15 cm (the given focal length).
Which one of the following materials cannot be used to make a lens?
The image formed by a concave mirror is observed to be virtual, erect and larger than the object. Where should be the position of the object?
Where should an object be placed in front of a convex lens to get a real image of the size of the object?
A spherical mirror and a thin spherical lens have each a focal length of –15 cm. The mirror and the lens are likely to be
No matter how far you stand from a mirror, your image appears erect. The mirror is likely to be
Which of the following lenses would you prefer to use while reading small letters found in a dictionary?
Name the type of mirror used in the following situations.
One-half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.
Answer: Covering the half portion of a convex lens will not affect the image making ability of the lens. The following two figures illustrate this.
Condition 1: When upper half of the lens is covered:
Condition 2: When the lower half of the lens is covered
An object 5 cm in length is held 25 cm away from a converging lens of focal length 10 cm. Draw the ray diagram and find the position, size and the nature of the image formed.
Answer: Given, height of object = 5cm
Position of object, u = - 25cm
Focal length of the lens, f = 10 cm
Hence, position of image, v =?
We know that;
Or, `v=(50)/(3)=16.66 cm`
Thus, distance of image is 16.66 cm on the opposite side of lens.
Now, magnification `= v/u`
Or, `m=(16.66 cm)/(-25 cm)=-0.66`
Or, `-0.66=(h_i)/(5 cm)`
Or, `h_i=-0.66xx5 cm=-3.3 cm`
The negative sign of height of image shows that an inverted image is formed.
Thus, position of image = At 16.66 cm on opposite side of lens
Size of image = - 3.3 cm at the opposite side of lens
Nature of image – Real and inverted.
A concave lens of focal length 15 cm forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram.
Answer: Given, focal length, f = - 15 cm
Distance of image, v = - 10 cm
Distance of object, v =?
Object distance can be calculated using the lens formula
Or, `u=-30 cm`
Negative sign shows that object is at 30cm in front of the lens.
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