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Investigatory Project on Water Pollution

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Investigatory Project on Water Pollution

Introduction


The addition of any substance (pollutants) which degrades the quality of water so that it either becomes health hazard or unfit for use is called water pollution. Most of the water surfaces usually contain small quantities of suspended particles, organic substances and a number of living organisms (bacteria, algae, fungi, protests, viruses etc.). Increase in the concentration of these substances pollutes water and makes it unfit for use. Similarly the presence of a low concentration of poisonous or toxic chemicals also pollutes water. The nutrient enrichment and algal growth result in the depletion of oxygen in water. It is called eutrophication. Water pollution due to organic waste is measured in terms of biological oxygen demand (BOD). It is the amount of dissolved oxygen needed by bacteria to decompose the organic wastes present in water.

 

Experiment 1

 

Aim

 

To test the presence of particulate matter in a given sample of water.

 

Materials Required

 

Cardboard box, electric bulb, beaker, sample of water.

 

Procedure

 

Take a cardboard box and prepare a Tyndal set up from it to test turbidity. Tyndal set-up can be prepared by making a cardboard box and make a pencil size hole in the box on opposite sides. Then fix a light source on one hole of the box. Inside the box at the centre, keep a beaker containing the sample of water. Switch on the light source and observe the sample of water through the hole. (Obtain the sample of water from different sources and compare their turbidity)

 

Observation

 

Suspended particulate pollutants may be observed.

 

Experiment 2

 

Aim

 

To study the biochemical oxygen demand of the given sample of water.

 

Materials and methods

 

Beaker, pipettes, burettes, conical flask, stirrer, ferrous sulphate solution, pheno saffranin (phenolphthaline + saffranin), Fehling solution, water sample.

 

Procedure

 

1. Take the burette, fill it with ferrous sulphate solution and fix it on a stand.


2. Take 50 ml of water sample to be tested in a beaker and add 2-3 drops of pheno saffranin and 10 ml of Fehling solution to the water sample.


3. Set the burette in such a way that its lower end remains in the water of the beaker.


4. Now run the ferrous sulphate solution and keep stirring the water sample till the pink colour disappears and the colour of water becomes light bluish green.


5. Note the initial and final readings of the burette and calculate the amount of ferrous sulphate used.


6. Repeat the experiment with different samples of water and record the volume of ferrous sulphate used to decolourise the pink colour.

 

Observations


Sl No:

Water Sample

Ferrous sulphate reading in burette

Volume Fe2SO4 used (X – Y)

Inference

Initial reading (X)

Final reading (Y)

1

2

3

4

5

 

 

 

 

 

 

 Conclusion

 

The oxygen dissolved in water oxidises ferrous sulphate to ferric sulphate. As a result, pink colour of the indicator disappears. The sample of water which requires higher volume of ferrous sulphate to decolourise the pink colour contains lesser dissolved oxygen and this has higher BOD. This shows greater pollution due to the presence of large number of microorganisms.

Transistor Characteristics Experiment with Readings

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COMMON EMITTER TRANSISTOR CHARACTERISTICS EXPERIMENT (CE Configuration Lab Report) (Class 12)


Aim


To study the static characteristic of a CE transistor


Apparatus


npn or pnp transistor (e.g. B.D 139 or B.D 140), a 2V and a WV batteries, rheostats, keys, milliammeter, microammeter, two low range voltmeters etc.


Procedure

Connections are made as shown in figure. The rheostat Rh1 is used to vary input voltage VBE and it is read from voltmeter V1. The input current IB is measured using a microammeter (µA ). The output voltage VCE is varied using Rh2 and readings are noted from voltmeter V2. The output current lC is measured by the milliammeter (mA).


Input characteristic


VCE is kept 1V and VBE is varied from zero in steps of 0.1 V(say) upto the rated voltage. IB is noted in each step. Graph is drawn with VBE along the x-axis and IB(µA) along the y-axis. [The reciprocal of the slope of the input characteristic gives the input resistance ri]


To draw the output characteristics


It is the graph drawn with output current IC - taken along y-axis and the output voltage VCE - taken along x-axis. IB is kept constant by adjusting Rh1, say, at 20 µA . Now VCE is increased in steps of say, 0.5 V upto the maximum rated voltage by adjusting Rh2. IC is noted in each step. A graph is drawn with IC along the y-axis and VCE along the x-axis. This gives the output characteristic corresponding to IB = 20µA. The experiment is repeated keeping IB constant, say 40 µA, 60µA, 80 µA, …. etc. and similar graphs are plotted. [The reciprocal of the slope of the graph gives the output resistance (r0))


The current gain β = (IC/IB)


Observation Table and Readings


Input Characteristics


VBE (V)

VCE = 2V

IB  (µA)

VCE = 4V

IB  (µA)

0

0

0

0.1

0

0

0.3

0

0

0.5

0

0

0.6

12

12

0.7

48

44

0.8

86

76

0.9

148

144

1

200

200

 

Output Characteristics


VCE (V)

IB (80µA)

IC

IB (120µA)

IC

0

0

0

0.2

9

16

0.4

12

17

0.6

14

17

0.8

14

17

1

14

17

2

14

17

3

14

17

4

14

17

  

Results


i. The characteristics of the transistor in CE configuration are drawn.

ii. The input resistance of the transistor = ……. Ω

iii. The output resistance of the transistor = ……… Ω

Concave Lens Experiment (Class 12) Readings

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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.

 

Observation Table 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)

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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

 

Observation Table 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.