Optical Instruments

Question 1

What happens when the object is outside F in concave lens (2)

Answer 1

-image is virtual
-reduced but upright

Question 2

What happens when the object is outside F in convex lens (3)

Answer 2

-image is real
-enlarged or reduced
-inverted

Question 3

What happens when the object is at F in convex lens (2)

Answer 3

-image formed at infinity
-no P ray

Question 4

What happens when the object is inside F in convex lens (5)

Answer 4

-No f ray as the ray does not pass focal point
-enlarged image
-example of magnifying glass
-upright
-virtual

Question 5

Define focal point (2)

Answer 5

-it is a specific point where the parallel rays of light either converge or appear to diverge after passing through or reflecting off an optical instrument

Question 6

State what is convex lens also called as (1)

Answer 6

-converging

Question 7

State what is concave lens also called as (1)

Answer 7

-diverging

Question 8

State the formula focal point (3)

Answer 8

1/ distance from object to lens + 1/distance between image and lens = 1/ focal point

(Di = + for real image , - for virtual)

(Do = + diverges)

Question 9

State the formula for magnification (3)

Answer 9

M = - (distance between image and lens / distance between object and lens )

Upside down = -
Right way up +

Question 10

What is the focal length convention for concave and convex lenses (2)

Answer 10

• f is positive for convex lenses
• f is negative for concave lenses

Question 11

What is the magnification convention for concave and convex lenses (4)

Answer 11

• m is + for upright images
• m is - for inverted images

If m less than one then it is reduced
If m greater than 1 its enlarged

Question 12

What is the image distance convention for concave and convex lenses (2)

Answer 12

• di is + real images
• do is - virtual images

Question 13

How does a human eye work (3)

Answer 13

-light passes through the cornea of the human eye
-it is then focused by the variable lens on the retina
-the eye produces a real, inverted image on the retina

Question 14

How does the human eye look at distanced or nearby objects (3)

Answer 14

-the ciliary muscle’s adjust the shape of the lens to alter at the focus point
-the ciliary muscles tense to focus on nearby objects
-they relax to focus on distant objects

Question 15

Define near point (1)

Answer 15

-it is the closest point to the eye that the lens is able to focus

Question 16

Define far point (1)

Answer 16

-it is the furthest point at which the eye can focus

Question 17

Go over lenses in combination (1)

Answer 17

-

Question 18

State and explain the concept of nearsightedness (5)

Answer 18

-a near sighted person has a far point that is finite distance away
-objects further away appear blurry
-this is due to the relaxed lens focusing too strongly
-so the image is formed in front of the retina
-after the far point the vision is fuzzy

Question 19

How to correct nearsightedness (2)

Answer 19

-a diverging lens is used (concave)
-it’s focal length is such that a distant object forms an image at the far point

Question 20

State the formula for refractive lower

Answer 20

= 1 / focal length
Si unit = m-1

Question 21

State and explain the concept of farsightedness(5)

Answer 21

• a person who has farsightedness can see the object far away easily
  -but cannot focus on closer objects
  -because the near point is too far away
  -the lens of the eye is not strong enough
  -fuzzy vision before the near point

Question 22

How to fix and correct farsightedness (3)

Answer 22

-a converging lens (convex)
-is used to increase the converging power
-the final image is last the near point

Question 23

What does the magnifying glass do with the near point (1)

Answer 23

-it moves the near point closer to the eye so the object appears closer and larger

Question 24

State the formula for angular size (1)

Answer 24

= height of the object / distance from the object to the eye

Question 25

What do you observe when object is far from the eye (1)

Answer 25

-smaller view hence smaller angle

Question 26

What do you observe when object is closer from the eye (3)

Answer 26

-larger view hence greater angle used
-angular angle size increases
-object can be seen with more detail when image taking up more space or retina

Question 27

State the formula for angular angle respective to near point (1)

Answer 27

Height of object / near point

Question 28

Look at the magnifying glass section

Answer 28

-

Question 29

State the formulas for maximum magnification (2)

Answer 29

M = angle with lens / angle without lens

= near point / focal length. (Image at infinity)

1 + near point / focal length (when image at near point)

Question 30

What does a compound microscope include (2)

Answer 30

Two converging lenses
-the eye pierce
-the objectives

Question 31

State the formula of magnification of objective (2)

Answer 31

M objective = - (distance b/w objective lens and image formed / distance from objective lens to object )
Or
- (distance b/w objective lens and image formed / focal length of objective

Question 32

State the formula for magnification of eye pierce (1)

Answer 32

Near point / focal length eye pierce

Question 33

Go over compound magnification (1)

Answer 33

-

Question 34

Lenses are generally used in air, however if a convex kens is placed in water how will its focal length change (3)

Answer 34

-in water the difference in refractive index of the lens and it’s surrounding is reduced
-the light will bend less in water
-as a result the focal length of a submerged kens is larger than the same lens in air