Microscope

Question 1

What does Fermat’s principle state?

Answer 1

the path taken by light in traveling from one point to another is such that the time of travel is a minimum

Question 2

What is the optical axis of a lens?

Answer 2

line connecting the centers of curvature of the spherical surfaces of the lens

Question 3

What is a converging lens?

Any other names?

Answer 3

= biconcave, positive lens

incident light parallel to the optical axis is focused at the rear focal point F

Question 4

What is a diverging lens?

Any other names?

Answer 4

= bi-convex, negative lens

incident light rays parallel with the optical axis emerges as if they originated from the front focal point

Question 5

What is the focal length?

Answer 5

f = distance of the focal point F to the principal plane

Question 6

What is the principal plane of a lens?

Answer 6

midline of the lens

Question 7

What is calculated by the Lens-makers equation?

Formula + Unit.

Answer 7

power of the lens = reciprocal of focal length

D = 1/f = (n₂₁ - 1) * (1/R₁ + 1/R₂)
in diopters [dpt] = [1/m]

• D = power of the lens
• n₂₁ = rel. index of refraction
• R = + if outside convex, - if concave

Question 8

What is a consequence of the lens-makers equation w/r/t the radii of the curvatures?

Answer 8

the smaller R → the shorter f → the larger D

Question 9

When does image formation occur?

What are the 3 principal rays in a diagram of image formation?

Answer 9

occurs, when a sufficient no. of light rays emerging from the object point converge at the image point

• parallel ray: parallel to optical axis
• focal ray: through front focal point
• central ray: through center of lens

(distance btw object/image point and principal plane is o and i, resp.)

Question 10

What are real and virtual images?

Answer 10

• real images = images where light actually converges
• virtual images = images from where light appears to have converged

Question 11

Differentiate btw imaging scenarios of a converging lens for different object distances.

Answer 11

• > 2f = real, inverted, diminished
• = 2f = real, inverted, same size
• f < 2f = real, inverted, magnified
• f = virtual, upright, magnified
• < f = virtual, upright, magnified

_{REMEMBER: <br></br>first 3: real + inverted<br></br>last 3: magnified<br></br> last 2: virtual + upright}

Question 12

What is lateral magnification of a lens?

How is it calculated?

Answer 12

M = lateral magnification = ratio of image and object size/ distance (I, O/ i, o resp.)

M = I/O = i/o

Question 13

Lens equation.

Answer 13

relates focal length with object and image distance

1/f = 1/o + 1/i

Question 14

How do 2 lenses in close contact to each other behave?

Answer 14

they add their power

D = 1/f₁ + 1/f₂ = D₁ + D₂

⇒ basis for correcting visual disorders

Question 15

What are the components of a microscope?

How does it work?

Answer 15

components:

• objective → objective lens
• eyepiece → eyepiece lens/ocular
• illuminating system
• specimen on specimen stage

function:

1. objective lens produces a real inverted magnified intermediate image M₀
2. ocular acts as a simple magnifier lens, produces a virtual erected magnified image Me of the intermediate image as an object
3. final image is virtual inverted and magnified

Question 16

How is the magnification power of a microscope calculated?

Answer 16

product of the magnification power of the objective and that of the eyepiece

M = M₀ * M_e

⇒ final image is virtual inverted and magnified