PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES

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Concave Lenses and Mirrors

Physics 1 – Concave Lenses and Mirrors

Concave LENSES AND MIRRORS


Aims



In this experimental tutorial you will first attempt a question which tests your knowledge and ability to draw principle ray diagrams concerning concave mirrors. Then you will perform the necessary experimental procedures to attain quality measurements, verifying theoretical prediction.


Part 1: Tutorial Question (10 mins)

PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES

    1. A real image is produced by a concave mirror on the same plane as the object as shown opposite. The size of a real image, i, is trebled if the object, o, distance is decreased from 0.75 m to 0.50 m.


  1. D

    Figure 1

    escribe the corresponding movement of the image.

  2. Calculate the radius of curvature of the mirror.

  3. Draw the principle ray diagram.

PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES

Part 2: Using a concave mirror on the optical bench (15 mins)


In this part of the experimental tutorial you will set up the necessary equipment on the optical bench and determine the focal length of a concave mirror via two different methods and therefore verify the answer.


Calculating f through the measurement of the radius of curvature of a concave mirror, R.



    1. Draw a ray diagram of this arrangement, showing the principle rays for an extended object transverse to the principle axis.


The distance from the mirror to the image is the radius of curvature of the mirror, R.



For a mirror, the radius of curvature is related to the focal length of the mirror, f, by the following equation:


R = 2f


    1. What is the focal length of your mirror?


Calculating f through the use of the mirror equation.



The mirror equation relates the focal length of a mirror, or lens, to the object and image distances as follows:


PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES


    1. Measure the object and image distances and hence calculate the mirrors focal length.



Part 3: Tutorial Question (10mins)


    1. PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES
      A thin diverging lens is placed on an optical bench. Parallel beams of light pass through the lens. On viewing the lens they appear as if they came from a point 20cm before the centre of the lens, as shown in figure 2. You want to use this lens to form a vertical virtual image that is a third of the height of the object.


(

Figure 2

a) Where should the object be placed?

(b) Draw a principle ray diagram.


Part 4: Using a concave lens on the optical bench (15 mins)


In this part of the experimental tutorial you will determine the focal length of a converging lens then observe the change when the same lens is used in conjunction with a diverging lens. Measuring this change accurately will enable you to calculate the focal length of the diverging lens.




    1. What is the focal length of the convex lens?



The power, P, of a lens is related to its focal length by the expression: PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES ,

where f is measured in metres, and the units of P are dioptres.



4.2 Calculate the power of this lens.



Beware of images formed by reflection, there will be two images formed by reflection from the lenses which you want to ignore.



4.3 Using your result for the power of the diverging lens calculate its focal length.


Part 5: Diverging lens and concave mirror (Optional)


PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES


Figure 3

    1. On the optical bench set up the arrangement shown in figure 3; use a concave mirror of known radius of curvature. Hence take measurements to obtain the focal length of the diverging lens.


Further work


The following questions are related to the topic covered by this experimental tutorial.



Demonstrators' Answers, Hints, Marking Scheme and Equipment List


Marking Scheme


Section

Mark

1.1a

0.5

1.1b

1

1.1c

0.5

2.1

1

2.2

1

2.3

1

3.1a

0.5

3.1b

0.5

4.1

1

4.2

1

4.3

1

Discretionary mark

1

TOTAL

10
















Answers

1.1(a) The image moves away from the mirror.

1.1(b) PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES

PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES

PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES m

1.1(c)

PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES


2.1 See Figure 1.


2.2/2.3 They should be very similar; differences tend to arise due to rounding of numbers.


3.1(a) From the information given:PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES , therefore PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES , i.e. PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES

so substituting into PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES gives PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES so PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES m

and PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES m

3.1(b)

PHYSICS 1 – CONCAVE LENSES AND MIRRORS CONCAVE LENSES


Part 4: The power obtained for the concave lens should be a negative value.


Equipment List


Concave mirror

Concave lens

Convex lens

Plane mirror

Light source

Screen with triangular hole

Pointer

3 x saddles

3 x holders


Example Numbers

Part 2:

Quantity

Pointer Measurement 1 (m)

Pointer Measurement 2 (m)

Length of pointer (m)

Length (m)

r

0.571

0.734

0.2

0.363

 

 

 

 

 

f

 

 

 

0.1815

 

 

 

 

 

s

0.571

0.934

0.2

0.563

s'

0.866

0.934

0.2

0.268

 

 

 

 

 

f

 

 

 

0.1816


Part 3:

Quantity

Pointer Measurement 1 (m)

Pointer Measurement 2 (m)

Length of pointer (m)

Length (m)

s1

0.571

0.698

0.2

0.327

s1'

0.571

0.698

0.2

0.327

f1

 

 

 

0.1635

 

 

 

 

 

s2

0.578

1.246

0.2

0.8680

s2'

0.578

1.246

0.2

0.8680

fc

 

 

 

0.4340

 

 

 

 

 

P1 (dioptre)

 

 

 

6.116208

Pc (dioptre)

 

 

 

2.304147

P2 (dioptre)

 

 

 

-3.81206

f2

 

 

 

-0.26233


5



2 SOLID STATE PHYSICS (INDIA) 45 (2002) XXXXXY PROCEEDINGS
20TH GAMOW INTERNATIONAL ASTRONOMICAL CONFERENCESCHOOL ASTRONOMY AND BEYOND ASTROPHYSICS
295407-electricity-sensing-waves-and-quantum-physics-mcq-topic-quiz-lesson-element


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