Recent

Search This Blog

Theme images by Storman. Powered by Blogger.

Followers

Recent in Sports

Home Ads

Comments

Ads

Random Posts

Featured Posts

Concave Lens Experiment (Class 12) Readings

- No comments


Concave Lens Experiment (Class 12) Readings


Aim


To determine the focal length of a concave lens using convex lens.


Apparatus


Concave lens, A convex lens of short focal length, Lens stands, illuminated wire gauze , Screen, Metre scale etc.


Principle


i. Lenses in contact


When a convex lens of focal length (f1) and a concave lens of focal length (f2) are placed coaxially in contact with each other, the equivalent focal length (F) of the combination is given by


1/F = 1/f1 +1/f2


Therefore, f2 = Ff1/(f1 - F)


The focal length (f2) of a concave lens is negative,


ii. Lenses out of contact


The focal length of the concave lens when it is out of contact with a convex tern it given by,


f2 = uv/(u- v)


where,

u —> Distance of the concave lens from the virtual object

v —> Distance of the concave lens from the image

 

Procedure

 

i. Lenses in contact

The focal length (f1) of the given convex lens (short focus) is determined by v method. The given concave lens is kept in contact with the convex lens. The focal length of the combination (F) is also determined by u - v method. Then focal length (f2) of the given concave lens can be calculated .

 

ii. Lenses out of contact

The given convex lens is fixed on a stand. It is fixed amid an illuminated wire gauze and a screen. The position of screen is adjusted to obtain a clear picture of the wire gauze on the screen at I. The concave lens (L) is fixed between the screen and the convex lens without any further arrangement. The distance amid the screen and the concave lens, LI1 = u is calculated. Now the screen alone is moved back to obtain a clear image I2 on the screen. The distance LI2 = v is measured. Using the values of u and v the focal length of the concave lens can be calculated. The experiment is repeated by changing the values of LI1 = u.

 

Observations and Readings


i. Lens in contact


Focal length (f1) of convex lens by displacement method

Trial

D cm

d cm

f1 = (D2-d2)/4D

Mean Focal length (f)

1

80

10.5

19.66

f1 = 19.74 cm

2

82

15

19.81

 

Lens used

No:

Distance between lens and object (u)

Distance between lens and image (v)

Focal length

Mean Focal length (f)

-

-

cm

cm

cm

cm

Combination of convex and concave lens

1

2

76.5

85.5

77.5

73.5

38.49

39.52

F = 39.005

 

Focal length of the concave lens, f2 = Ff1/(f1-F) = 39.96 cm = 39.96 x 10-2 m

 

i. Lenses out of contact


No:

Distance of first image I1 from concave lens (LI1 = u)

Distance of second image I2 from concave lens (LI2 = v)

Focal length (f2)

 

cm

cm

cm

1

2

3

29

39.5

32.1

15.5

20

16.5

-33.95

-40.51

-33.29

 

Mean focal length, f = -35.91 cm = -35.91 x 10-2 m

 

Results


Focal length of the concave lens


i. by lenses in contact method = -39.96 x 10-2 m

ii. by lenses out of contact = -35.91 x 10-2 m

 

Viva Questions and Answers

 

1.Give the nature, position and size of the image formed by a concave lens at different positions of the object.


Position of

Nature

Size

Erect or inverted

Object

Image

At infinity

At F

Virtual

Diminished

Erect

Any other position

Between F and C

Virtual

Diminished

Erect

 

2. What do you understand by the term 'focal plane' of a lens?


It is a plane perpendicular to the principal axis and at a distance equal to the focal length of the lens.


3. What is spherical aberration in a lens? How is it eliminated?


It is the inability of a lens to focus all the refracted rays to a single point. It can be minimised by using stops.


4. What is chromatic aberration? Flow is it eliminated?


The inability of a lens to focus all the colours to a single point is called aberration.


Chromatic aberration can be eliminated by combining a convex lens and a concave lens of suitable focal length and material (achromat).


5. What is lens maker's formula?


1/f = (n-1)[1/R1-1/R2]


6. Why is the focal length of a concave lens negative?


This is because the focal length is measured in a direction opposite to the incident ray. 

Convex Mirror Experiment with Readings (Class 12)

- No comments


Convex Mirror Experiment with Readings (Class 12)

Aim

 

To find the focal length of a convex mirror using a convex lens

 

Apparatus

 

A Convex mirror, Convex lens, Screen, Stand, Illuminated object, Scale.

 

Principle

 

When light is incident normally on a convex mirror, after reflection, the rays retrace their path. Thus image is obtained side by side with the object. Using this principle, the centre of curvature of the mirror can be located and radius of curvature 'R' can be calculated.

The focal length of the mirror, f = R/2

 

Procedure

 

The convex lens is mounted on a stand in front of an illuminated wire gauze. The screen is placed on the other side of the lens. The position of the screen is adjusted to obtain a well defined sharp image of the wire gauze on the screen. Now the convex mirror is placed between the lens and the screen with its reflecting surface facing towards the lens. The position of the mirror is adjusted so as to get the image of the object (wire gauze) side by side with it. The distance between mirror and the screen is measured. This gives the radius of curvature (R) of the mirror. The experiment is repeated by changing the distance between the object and the screen. Each time focal length of the mirror is calculated using the formula,

f = R/A

 

Observations and Readings

 

Distance between the mirror and the screen

1

2

3

4

Mean R cm

32.5

32

33

32.4

32.5

 

Mean R = 32.5 cm

f = R/2 = 16.25 m = 16.2 x 10-2 m

 

Result

 

Focal length of the convex mirror = 16.2 x 10-2 m

Power, 1/f = = 0.0615 x 102 = 6 Dioptre

 

VIVA QUESTIONS AND ANSWERS

 

1. Define principal axis of a mirror.

 

It is a straight line passing through the centre of curvature and pole of the mirror.

 

2. Define principal focus of a mirror.

 

A narrow parallel beam of light parallel and close to the principal axis of a mirror, after reflection converges to a fixed point on the principal axis if the mirror is concave or appears to diverge from a fixed point on the principal axis if the mirror is convex. This fixed point is called the principal focus.

 

3. What is focal length?

 

It is the distance between pole and principal focus.

 

4. What is parallax?

 

It is the relative displacement between the two objects when they are at different distance from the eye.

 

5. Give the position, nature and size of the image formed by a convex mirror at different positions of the object. 


Position of

Nature

Size

Erect or inverted

Object

Image

At infinity

At F

Virtual

Diminished

Erect

At any point

Between F and P

Virtual

Diminished

Erect

 

6. What is spherical aberration in mirror?

 

It is the inability of a spherical mirror to focus both marginal and paraxial rays into a single point.

 

7. How is spherical aberration minimised?

 

Using stops or using parabolic mirrors.

 

8. Give some applications of spherical mirrors.

 

Concave mirror - Used in

(1). Shaving mirror

(2). Reflecting type astronomical telescope

(3). Search light and in torches.

Convex mirror — Used in automobiles as rear view mirror.

 

9. Why a concave mirror of small aperture forms a sharp image?

 

This is because it is free from spherical aberration.


Concave Mirror Experiment with Readings (Class 12)

- No comments


Concave Mirror Experiment with Readings (Class 12)


Aim


To determine the focal length of the given, concave mirror


Apparatus


Concave mirror, illuminated wire gauze stand, screen, meter scale.


Principle

i. For distant object method, the distance between the screen and the mirror is the focal length.


ii For normal reflection method the distance between the object and mirror is the radius of curvature (R) of the mirror, then focal length f = R/2.


iii. By u - v method, focal length f = uv/(u+ v)

where, u - Distance between object and mirror (object distance)

v - Distance between image and screen (image distance)


iv. From u-v graph,  f = (OA+OB)/4

where, OA and OB are the co-ordinates at the point where, u = v.


v. From 1/u — 1/v graph, f = 2/(OA + OB)

where, OA and OB are the intercepts on the X and Y axis respectively.

Effect of Temperature on the Rate of Reaction Experiment

- No comments

 

A lab report on investigation on the effect of temperature on the rate of reaction experiment between sodium thiosulphate and HCl

Introduction

 

According to kinetic theory, reactions occur when the reacting particles collide with each other. When the temperature is increased particles get more energy and hence the frequency of collision increases. Consequently the rate of the reaction also increases.

 

Aim


The aim of this investigatory project is to investigate the effect of temperature on the rate of a reaction. The reaction used for this purpose is that between sodium thiosulfate and dil. hydrochloric acid.


Na2S203 + 2HCl => 2NaCl + SO2 + H20 + S


The progress of the reaction is followed by the opaqueness developed by the precipitation of sulphur when the reaction is carried out at different temperatures.


Requirements


1. 100 mL beakers

2. Sodium thiosulphate

3. HCI acid

4. Water bath

5. Thermometer

6. Stop watch


Procedure


Measure out 10 mL of 0.2M sodium thiosulphate solution into a 100 mL beaker. Add 40 mL water to it and heat in a water bath. Also place 5mL 2M HCl in a separate test tube in the water bath. When the temperature of the bath and also of the solutions reach 40°C, transfer hydrochloric acid to the sodium thiosulphate solution, immediately starting a stop-watch. Take out the beaker quickly, swirl the contents, wipe out the water outside the beaker and place it on a white paper with a cross mark. Look from above. Stop the stop-watch when the cross is no-longer visible. Note the temperature of the solution. Tabulate the time and temperature.


Repeat this experiment several times such that the measurements are taken at 50°C, 60°C, 70°C, each time determining the time. Carry out the same experiment at room temperature (30°C) also. Tabulate the results.

 

No:

Temperature

Volume of thiosulfate in mL

Volume of water in mL

Volume of HCl in mL

Time taken for disappearance of the cross

1

30°C

10

40

5

-

2

40°C

10

40

5

-

3

50°C

10

40

5

-

4

60°C

10

40

5

-

5

70°C

10

40

5

-

 

 

The results clearly indicate that as the temperature of the reaction increases, the time of disappearance of the cross decreases. It means that the rate of the reaction increases with increase in temperature.


Conclusion


The rate of reaction increases with increase in temperature.

 

VIVA QUESTIONS WITH ANSWERS


1. What is the effect of temperature on the rate of a reaction?


Ans: Rate of a reaction increases with increase in temperature.


2. How will you explain the increase in the rate of a reaction with increase in temperature?


Ans: According to kinetic theory, a reaction occurs by the collision of the reacting molecules. As the temperature increases, the number of collisions also increases.


3. How does the frequency of collision increase with increase in temperature?


Ans: Kinetic energy of the molecules increases with increase in temperature. Hence the frequency of collision also increases.

Effect of Concentration on Rate of Reaction Experiment

- No comments

 

A lab report on study of the effect of concentration on rate of chemical reaction experiment between Sodium Thiosulphate and Hydrochloric Acid (HCl)

Introduction

 

According to the law of mass action, the rate of a reaction is proportional to the active mass or the molar concentration of the reactant at a given temperature.


Aim

 

The aim of this project is to determine the effect of concentration on the rate of a reaction.

 

Principle

 

The reaction which is used is that between sodium thiosulfate and hydrochloric acid

 

Na2S2O3 + 2HCI --> 2NaCI + SO2 + H2O + S

 

Since this reaction produces a precipitate of sulphur from two colourless solutions, the intensity of the precipitate at any given time represents the extent of the reaction. The way in which the intensity of the precipitate is measured is by carrying out the entire reaction in a beaker and by placing the beaker and its contents on a white paper with a cross marked on it. The time for the disappearance of the cross when the contents of the beaker are viewed from above will give a measure of the time taken for a certain fraction of the reaction to occur.

 

Requirements

 

1. 100 mL beakers

2. Sodium thiosulphate

3. HCI acid

4. Stop watch

 

Procedure

 

Place 50cm3 of 0.2M sodium thiosulphate solution in a 100cm3 beaker. Add 5cm3 2M HCl to it and start a stop-watch at the same time. Swirl the beaker carefully a couple of times and place it on a white card with a cross marked on it. Observe the cross by looking down through the solution from above the beaker and stop the stop-watch at the moment the cross disappears and note the time and record.


The concentration of the thiosulphate solution is varied by taking 40, 30, 20 and 10 cm3 of 0.2M thiosulphate solution and making the total volume up to 50cm3 each time by adding water. Add 5cm3 of 0.2M HCI to each as above and note the time taken for the disappearance of the cross in each case and record.


No:

Volume of thiosulfate (0.2M) in cm3

Volume of water in cm3

Volume of HCl

Time taken for disappearance of the cross

1

50

0

5

-

2

40

10

5

-

3

30

20

5

-

4

20

30

5

-

5

10

40

5

-

 

It is found from the table that as the concentration of the thiosulphate solution increases, the time for the cross to disappear from view decreases. 


 Discussion and Conclusion

 

Since the rate of the reaction is inversely proportional to time (a fast reaction takes a short time and a slow reaction takes long lime), we can conclude that as the concentration of the sodium thiosulphate solution increases, the rate of the reaction also increases.

 

VIVA QUESTIONS WITH ANSWERS

 

1.  What is law of mass action?

 

Ans: Rate of a reaction is directly proportional to the product of active masses of the reactants.

 

2. What will you observe when dil.HCI is added to sodium thiosulphate solution?

 

Ans: Formation of a yellow precipitate.

 

3. What is the yellow substance produced?

 

Ans: Sulphur

 

4. Write the equation for the reaction between sodium thiosulphate and HCl

 

Ans: Na2S2O3 + 2HCl --> 2NaCl + SO2 + H2O + S

 

5. What is the effect of concentration on the rate of a reaction?

 

Ans: As the concentration of the reactant increases the rate of reaction also increases.