Advertisements
Advertisements
प्रश्न
An object of height 4 cm is placed at a distance of 15 cm in front of a concave lens of power, −10 dioptres. Find the size of the image.
Advertisements
उत्तर
Object distance u = -15 cm
Height of object h = 4 cm
Power of the lens p = -10 dioptres
Height of image h' = ?
Image distance v = ?
Focal length of the lens f = ?
We know that:
`p=1/f`
`f=1/p`
⇒`f=1/-10`
⇒ `f=-0.1m =-10 cm`
From the lens formula, we have:
`1/v-1/u=1/f`
`1/v-1/-15=1/-10`
⇒`1/v+1/15=-1/10`
⇒`1/v=-1/15-1/10`
⇒`1/v=(-2-3)/30`
⇒`1/v=-5/30`
⇒`1/v=-1/6`
⇒`v=-6` cm
Thus, the image will be formed at a distance of 6 cm and in front of the mirror.
Now, magnification m =`v/u=(h')/h`
or `(-6)/(-15)=(h')/4`
`h'=(6x4)/15`
`h'=24/15`
∴`h'=1.6 cm`
संबंधित प्रश्न
Find the focal length of a lens of power −2.0 D. What type of lens is this?
A student uses a lens of focal length 40 cm and another of –20 cm. Write the nature and power of each lens
What can you see in a completely dark room? If you switch on an electric bulb in this dark room as a light source, explain how you could now see:
(a) the electric bulb
(b) a piece of white paper
What is the power of a convex lens of focal length 0.5 m?
A converging lens has focal length of 50 mm. What is the power of the lens?
A diverging lens has focal length of 3 cm. Calculate the power.
The power of a lens is + 0.2 D. Calculate its focal length.
The optician's prescription for a spectacle lens is marked +0.5 D. What is the:
(a) nature of spectacle lens?
(b) focal length of spectacle lens?
A convex lens of focal length 25 cm and a concave lens of focal length 10 cm are placed in close contact with one another.
(a) What is the power of this combination?
(b) What is the focal length of this combination?
(c) Is this combination converging or diverging?
What is the unit of power of a lens? Define the unit of power of a lens.
Define the term focal length of a lens.
Name the type of lens whose power is positive.
The image of an object formed by a lens is real, inverted and of the same size as the object. If the image is at a distance of 40 cm from the lens, what is the nature and power of the lens ? Draw ray diagram to justify your answer.
Mohan obtained a sharp inverted image of a distant tree on the screen placed behind the lens. He then moved the screen and tried to look through the lens in the direction of the object. He would see:
(1) a blurred image on the wall of the laboratory.
(2) an erect image of the tree on the lens.
(3) no image as the screen has been removed
(4) an inverted image of the tree at the focus of the lens.
A symmetric double convex lens in cut in two equal parts by a plane perpendicular to the principal axis. If the power of the original lens was 4 D, the power a cut-lens will be
A convex lens produces a double size real image when an object is placed at a distance of 18 cm from it. Where should the object be placed to produce a triple size real image?
A stick partly immersed in water appears to be bent. Draw a ray diagram to show the bending of the stick when placed in water and viewed obliquely from above.
The power of the magnifying glass depends on the distance of the magnifying glass from object.
If focal length of a convex lens is 20 cm at what is the power of the lens?
The focal length of a concave lens is 20 cm. The focal length of a convex lens is 25 cm. These two are placed in contact with each other. What is the power of the combination? Is it diverging, converging or undeviating in nature?
A point object is placed at O in front of a glass sphere as shown in figure.
Show the formation of the image by the sphere.
The focal length of a double convex lens is equal to the radius of curvature of either surface. What is the refractive index of its material?
In what unit is the power of a lens expressed?
1 D is equivalent to:
A negative power of a lens indicates a:
When a lens is placed in a liquid, light refracts at:
When a lens is placed in a liquid, the total power of the lens is:
If the lens material and the surrounding liquid have the same refractive index (\[n_2 = n_1\]), then:
If the refractive index of the lens material is less than that of the surrounding liquid (\[n_2 < n_1\]), then:
