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Mirror and Lens Problems for Class 10

This article present the general Glossary of Mirror and lens and step by step method to solve Mirror and Lens problems

Glossary of Mirror and Lens

Plane Mirror
A plane mirror is a mirror with a planar reflective surface. For light rays striking a plane mirror, the angle of reflection equals the angle of incidence.It always form virtual image

Concave or Converging Mirrors
A curved mirror that has its center farther away from you than its edges is called a concave mirror. A concave mirror tends to reflect parallel rays through a point called its focus – in other words a concave mirror converges light. Therefore concave mirrors are often referred to as converging mirrors. This converging effect makes sense if you imagine a concave mirror to be an array of small plane mirrors.You can demonstrate the converging of parallel light rays by a concave mirror quite dramatically for yourself. A relatively small concave mirror placed in the sun will gather enough light to ignite a small piece of paper quite quickly

Convex or Diverging Mirrors
It is  a curved mirror that has its center closer to you than its edges is called a convex mirror.A convex mirror tends to reflect parallel rays so that they spread out, or diverge. For this reason, convex mirrors are often referred to as diverging mirrors. This diverging effect makes sense if you think of a convex mirror as an array of small plane mirrors.

Convex lens
It is also called converging lens, real or virtual rays come together at a point

Concave lens

It is also called diverging lens because spreads light out

Real Image
when light really comes together-will show up on a screen

Virtual Image
light rays not really coming together-never on a screen

How to solve the Mirror and Lens Problems

Step 1) The concept of flats mirror,concave mirror/lens and convex mirror/lens should be clear. The formula used are Mirror equation/lens maker equation and Magnification equation.
Step 2) The sign convention and ray diagram should also be clear
Step 3) Read the Problem statement clearly and find out the clues in the problem. Find the known and unknown variable. This step is crucial and you need to apply the sign convention also.
Step 4) Draw a ray diagram. The more careful you are in constructing this, the better idea you’ll have of where the image is.
Step 5) Apply the appropriate  equation to determine the unknown. You may have solve two simultaneous equation in some case.
Step 6) The result of the steps 4 and 5 are consistent with each other.

How to solve Multiple Lenses Problem

Step 1)Do the first lens as if the others weren’t there.
Step 2)Use the image formed by this lens as the object of the next lens
step 3)Repeat this process for all the lenses in the system
Step 4)The total magnification is just the product of the individual magnifications of each lens.

Some Mirror and Lens Problems

Question (1)

An object is placed 25 cm in front of a concave mirror of focal length 60 cm. Calculate the image distance and the magnification. Characterize the image.

Question (2)

An object is placed 25 cm in front of a convex mirror of focal length 30 cm. Calculate the image distance and the magnification. Characterize the image.

Question (3)

Two plane mirrors are inclined to one another at an angle 30. A ray traveling in the plane as shown below is incident on one of the mirrors. Applying the Law of Reflection, show that the path of the ray after the two reflections is deviated by an angle which is independent of the angle of incidence.

Question (4)

Ram obtains a blurred image of an object on the screen by using the concave mirror, In order to obtain sharp sharp image on the screen, he will have to shift the mirror
(a)to a position very far from screen
(b)towards the screen
(c) away from the screen
(d) either away or towards depending on the position of the object

Question (5)

Refractive index of media A, B, C and D are
A 1.31
B 1.52
C 1.45
D 1.64

In which of the four media is the speed of light (i) maximum (ii) minimum?

Question (6)

An object of size 5 cm is kept at a distance of 25 cm from the optical center of a converging lens of
focal length 10cm. Calculate the distance of the image from the lens and size of the image.

Question (7)

Explain reasons for each of the following:
(i) The sky appears to be blue during day time to a person on earth.
(ii) The sky near the horizon appears to have a reddish heu at the time of sunset and sunrise.
(iii) The sky appears dark instead of blue to an astronaut.
(iv) The stars appears to twinkle.
(v) The planets do not twinkle.

Question (8)

How does the speed of light change as the index of refraction increases?

Question (9)

How does the size of the critical angle change as the index of refraction increases?

Question (10)

Could an index of refraction ever be less than 1? What would this imply about the speed of light in that medium?

Question (11)

A 2.25-cm-tall object is 8.5 cm to the left of a convex lens of 5.5-cm focal length. Find the image position and height

Question (12)

Does your bathroom mirror show you older or younger than your actual age?

Question (13)

A concave makeup mirror is designed so that a person 25 cm in front of it sees an upright image magnified by a factor of 2. What is the radius of curvature of the mirror?

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