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Effect of Herbicides on lawn weeds Investigatory Project

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Investigatory Project on Effect of Herbicides on lawn weeds

 

STUDY OF THE EFFECT OF A HERBICIDE ON LAWN WEEDS (To compare the effect of a herbicide on monocotyledonous and dicotyledonous plants)

 

Introduction

 

Weeds are unwanted plants which grow in cultivated fields and compete with the useful plants for the resources. They compete for the light, space, nutrients, water and reduce the crop yield. Weeds acts as alternate host for certain diseases and these help in spreading the diseases. Many weeds cause allergy and other skin diseases in human beings. Weeds can be removed from the fields, play grounds and lawns either by mechanical or chemical method. In chemical method, certain chemicals are used to kill the weeds. These chemicals are called weedicide. The synthetic auxins like 2, 4-D (2, 4 Dichlorophenoxy acetic acid) interferes with the translocation of carbohydrate and thus kills the plants. Dicot and monocot plants respond differently to different concentrations of 2, 4-D. Specific concentrations of 2, 4 - D can destroy dicot plants, while monocot plants remain unaffected. Therefore, 2, 4 - D is commonly used as selective herbicide.


Materials and Methods

 

2, 4 - D, sprayer, beakers, measuring cylinder, cord, nails etc were collected. Then prepared ten gram 2, 4-D was dissolved in 3 ml of ethanol. This solution was mixed with 100 ml of distilled water. A weed growing lawn was selected for the study. A square area was masked out by using nails and cord. 2, 4 - D solution was spread over the selected area once in a week.

 

Observation and Results

 

After a few days the marked and treated area was observed. The broad leaved dicot plants showed wilting after a day or two and gradually died. But the monocot plant such as grass remain unaffected.

 

Discussions and Conclusions

 

2, 4 - D had killing effect on broad leaved dicot plants and not on monocot plants.

 

Model Viva Questions and Answers

 

1. What are weeds?

Weeds are unwanted plants which compete with economically useful plants for the resources and reduce the yield.

 

2. Name a few common weeds.

Amaranthus, Alternanthera, Convolvulus, crotton sps. etc.

 

3. What are herbicides?

Herbicides are chemical substances which are used to kill herbs.

 

4. Why 2, 4 - D is used as a common herbicides for lawns?

Because 2, 4 - D kills broad leaved dicot plants without affecting narrow leaved monocot plant or the grass of the lawn.

 

5. Name a few commonly used herbicides.

2, 4 - D, Atrazine, Simazine etc.


References

 

1. G. Ray Noggle and George J. Fritz. Introductory Plant Physiology. Prentice, Hall of India Pt. Limited. New Delhi.

2. William. G. Hopkins, Introduction to Plant Physiology. John Wiley and Sons Inc. NewYork.

Zener Diode Experiment Viva Questions

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Zener Diode Experiment Viva Questions and Answers

 

1. What is a Zener diode?

 

A junction diode which can operate in the reverse breakdown voltage region is called a Zener diode.

 

2. Is Ohm's law obeyed in a semiconductor or not?

 

In a semiconductor, Ohm's law is valid only for low electric fields.

 

3. What is meant by a junction diode?

 

When a p-type semiconductor is fixed with n-type semiconductor, it forms a junction diode.

 

4. What is meant by forbidden gap?

 

The band separating the valance band and the conduction band is called forbidden gap.

 

5. What is meant by reverse current?

 

The reverse current is the current in the p-n junction diode circuit, when the junction is reverse biased.

 

6. What is meant by reverse breakdown?

 

Sudden increase in reverse current of a p-n junction diode when a definite reverse voltage is applied is called reverse breakdown.

 

7. What is the cause of reverse breakdown?

 

The cause of reverse breakdown will rupture a very large number of covalent bonds due to high reverse voltage applied.

 

8. What is zener current?

 

The value of reverse current after the zener breakdown is called zener current.


9. What is meant by the break down voltage of a diode


Materials are known as Conductors, Semiconductors, and Insulators, based on their electrical features. Materials that can easily conduct electricity are conductors. In comparison, insulators are categorised as materials that do not conduct any electricity. Among conductors and insulators lie the features of semiconductor materials. Researchers have observed during their work with insulators that when a certain amount of electricity is applied to them, insulator material can be made to act as a conductor. Breakdown was named for this phenomenon, and the minimum voltage at which this happens is known as Breakdown Voltage. For various materials, these voltage levels are distinct and often depend on their physical properties.


The main use of zener diodes in electronic circuits is they can be used as basic building blocks. In order to provide a reference voltage to the electronic circuits, zener diodes are used. Zener diodes works in the breakdown regions of the diode. 


Generally zener diodes are huge diodes, so that they can work in the reverse biased regions.  Due to the zener effect, the breakdown takes place. When the electric field of the reverse-biased P-N diode is increased in the Zener effect, tunnelling of the valence electrons into the conduction band occurs. This results in an improvement in the reverse current of the minority charge carriers. The Zener effect is known as this phenomenon, and the minimum voltage at which this phenomenon begins is known as the Zener voltage breakdown.


10. What are the differences between an ordinary diode and zener diode?


The main differences between ordinary diode and zener diodes are:


(i) The operation of diode is uni-directional, while the zener diode operates bi-directionally in both forward and reverse biased directions.


(ii) For an ordinary diode and a zener diode, the doping characteristics is also different. The conventional diode is moderately doped, while the zener diode is sharply doped.


(iii) In normal P-N Junction diodes, the breakdown voltage is high, but in case os zener diodes, the breakdown voltage is sharp.


(iv) It is not possible to operate a conventional diode in reverse biased mode, but it is possible to operate a zener diode in reverse biased mode.


(v) The main use of conventional diodes are they can be used in clipper, clamper, rectifiers, etc. The main use of zener diode is in voltage regulator circuits.


11. Distinguish between zener break down and avalanche break down?


Avalanche Breakdown:


(i) The condition of occurrence of Avalanche breakdown is when both sides of the PN junction are lightly doped and high depletion layer.


(ii) In Avalanche breakdown, it has a weak electric field across the depletion region.


(iii) Covalent bonds are broken due to the collision with valence electrons and electron-holes are created.


(iv) In Avalanche breakdown, from the applied potential,  the charge carriers acquires energy and produces  more carriers. This process is termed as Avalanche multiplication and the breakdown is termed as the avalanche breakdown.


Zener Breakdown


(i) The depletion layer is narrow and zener breakdown occurs when both sides of the PN junction are strongly doped.


(ii) Zener breakdown produces a a strong electric field by applying a small reverse bias voltage.


(iii) In Zener Breakdown, the covalent bonds are braked by the field, hence producing large number of electrons and holes.


(iv) The electrons and holes yields to the reverse saturation current (Zener current). This zener current and the applied voltage is independent.


12. What is the use of a zener diode


The main uses of zener diodes are:

(a) Zener diode can be used as constant - voltage diodes

(b) It can be used as voltage detection devices.#

(c) It provides voltage clipping


13. Give the Symbol of Zener Diode

14. Aim of Zener Diode Experiment

 

(i) To draw I—V characteristic of a zener diode under reverse biased condition.

(ii) To determine the zener breakdown voltage from the graph.

 

15. Apparatus of Zener Diode Experiment

 

A zener diode (ex: FZ 6.2 A), milliammeter, multimeter or dc voltmeter, dc regulated supply which can be varied from 0 to 10 V in steps of IV, 100 Ω resistor, etc.

 

16. Procedure of Zener Diode Experiment

Connections are made as shown in the figure. The type of zener diode is noted. Its breakdown voltage Vz, maximum current rating and maximum power rating are noted from the data book. (This helps us to fix the value of current limiting resistor R and the range of voltmeter or multimeter).


The regulated supply is switched on. The voltage V across the zener diode is measured between the points C and D by the multimeter and the zener current I is noted in the milliammeter. The zener voltage V is varied from zero in steps of, say, IV by varying the input voltage Vi of the regulated till the zener current I is about 50% of the maximum rated value of the zener current. In each step the zener current I is noted. The input voltage Vi is also measured in each step across the points A and B by the multimeter. Once the break down occurs zener voltage remains almost constant.

A graph is plotted between I and V in the third quadrant of the graph paper This gives the I—V characteristic of the zener diode. From the graph the breakdown voltage Vz of the zener diode is noted at any point on the steep portion of the graph. The dynamic resistance of the diode is also calculated at the point.

Investigatory Project on Pollen Germination

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INVESTIGATORY PROJECT ON STUDY OF RATES OF POLLEN GERMINATION OF VARIOUS SPECIES IN SUGAR AND BORON SOLUTION (BIOLOGY)

Introduction

 

Pollen grains or microspores are the male gametophyte of angiosperms. The process of transfer of pollen grains from anther to the stigma of a flower is called pollination. Pollen grains germinate after reaching on the stigma. A pollen grain has usually two cells, generative cells and vegetative cell at the time of pollination. A mature pollen grain has 2 layers outer thick exine and inner thin intine. Here and there in the exine small thin areas are present, they are called germ pores. During pollen germination a pollen tube grows out from the pollen grain through a germ pore. The generative cell move down to the pollen tube and divide into two male gametes. The pollen tube enters the embryosac and releases the male gametes to ensure fertilisation. The rate of pollen germination differs in different plant species.

 

Materials and Methods

 

Flowers of different plants, cavity slides, sucrose, boric acid, distilled water, beaker, micro-scopes etc were collected.

 

A nutrient solution was prepared by dissolving 1 gm of sucrose in 100 ml distilled water. Five clean cavity slides were taken and a few drops of nutrient solution was put in the cavity of each slides. In this nutrient solution the pollen grains from different flowers were dusted. Similarly another nutrient medium was prepared by dissolving 1 gm of boric acid in 100ml of distilled water and the experiment was repeated with the pollen grains of flowers of different plants.

 

Observation and Results

 

Observe each slide containing sucrose solution one by one under five different microscopes after 5 minutes and after one minute each. Similarly observe each slide containing boric acid solution one by one under five different microscopes. Record the observations in the tabular column given below.

 

Rates of pollen germination of different species of plants in sucrose solution


Rates of pollen germination of different species of plants in boric acid solution


Discussions and Conclusions

 

The viable pollen grains germinate in both the nutrient solutions. But the germination percentage varies in boric acid solution and sucrose solution. This also depends upon the species variation and time factor.

 

References

 

Give a list of books and other reading materials you have referred for the present project work.

 

Viva Questions and Answers

 

1. What are viable pollen grains?


The pollen grains which are able to germinate and produce male gametes are called viable pollen grains.

 

2. Why a nutrient solution is required for pollen germination?


Because nutrients are essential for the growth of pollen tube.

 

3. Where do pollen grains germinate?


Pollen grains germinate on the stigma. 

Boyle's Law Experiment for Class 11

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Boyle's Law Experiment for Class 11

 

EXPERIMENT – 1 (Grade 11)


BOYLE’S LAW I (Using Boyle's Law)


Aim:


To verify Boyle's law using Boyle's Law apparatus and to determine the atmospheric pressure.

 

Apparatus:


Boyle's law apparatus consists of a uniform glass tube AB closed at one end. The open end is connected to a reservoir R, by means of a rubber tube. The reservoir contains mercury. The glass tube contains pure dry air. The glass tube and the reservoir are fitted to a vertical graduated board. The reservoir can be raised or lowered and can be fixed at any position. A scale is fixed between AB and R.

 

Principle:


According to Boyle's law, at constant temperature, the pressure of a given mass of gas is inversely proportional to its volume.

ie., P x V =a constant.

Since the volume of air in the glass tube is directly proportional to the length 'l'.

P x l = constant

 

Procedure


a. To verify Boyle's law


i. The atmospheric pressure H is noted from a Fortin's barometer.


ii. The reservoir is adjusted till the mercury levels in the AB and the reservoir are the same. Now, the pressure of air inside AR is equal to the atmospheric pressure (H). The reading of the closed end of the glass tube AB is noted as R1. The length of air column (l) is measured.


iii. The reservoir is raised and fixed at a particular height. (Mercury level in R is above than that in AB). The difference in levels of mercury in the reservoir and in the closed tube AB is noted as h. The pressure P of air inside the tube in H + h.


iv. The reservoir is lowered and fixed at a particular height. (Mercury level in R is below than that in AB). The difference in levels of mercury in the reservoir and the closed tube is noted as h. The length of the air column l is measured. The pressure P of air inside the tube is H — h. Repeat the experiment with mercury level in the reservoir above that in the tube AB and also with mercury level in the reservoir below that in the tube AB. Do experiment three times in each case.

In each case P x l = constant, verifies Boyle's law. A graph between P and 1/l is found to be a straight line.

 

b. To determine the atmospheric pressure.


Applying Boyle's law

P x l = constant

i.e., (H ± h1) l1 = (H ± h2)l2

(H + h1)l1 = (H + h2)l2 

H = (h2l2-h1l1)/(l1-l2)


where h1 and h2 are the difference in mercury levels in the two limbs in any two cases and l1 and l2, are the corresponding lengths of the air column. (If the mercury level in the reservoir is below that in the glass tube AB, then height is taken as negative and vice versa.)


A graph is drawn with h along the X - axis and 1/l along the Y- axis. The X intercept (negative side of the X - axis) gives the atmospheric pressure (H). (The sign of h must he considered in drawing the graph)

 

Observations and Readings

 

Plot, P-1/l graph


i. To verify Boyle’s law


Atmospheric pressure, H = …….. cm of Hg

Reading of the closed end A of the tube = R1 = …….. cm


ii. To determine the atmospheric pressure


Mean H = ……..cm of Hg = ……..m of Hg


Plot h-1/l graph

 

Atmospheric pressure, H(OB) = ……… cm of Hg = ………m of Hg

 

Results:


i. P x l = constant, verifies Boyle's law

ii. Atmospheric pressure,

a. By calculation =.......... m of Hg

b. From graph = ………. m of Hg

 

EXPERIMENT – 2 (Grade 11)


BOYLE’S LAW II (Using Quill Tube)

 

Aim: To study the variation in volume with pressure of a given mass of gas at constant temperature.


Apparatus: Quill Tube, Stand, Meter scale etc.

A quill tube is a uniform tube closed at one end. By means of a pellet of mercury, a certain mass of air is enclosed in the tube.

 

Principle:


According to Boyle's law, at constant temperature, the pressure of a given mass of gas is inversely proportional to its volume.

ie, P x V = a constant.

Since the volume of air in the quill tube is directly proportional to the length ‘l'

P x l = constant

 

Procedure


(a) Horizontal Position


The quill tube is held horizontally. The length of air column is measured. Vertical height at the two ends of mercury thread from the table are measured. The difference between them gives vertical height `h' of the mercury thread, Here h = 0. Pressure inside the tube = H


(b) Vertical Position (Closed end downwards)


The quill tube is then held vertically by means of a stand with closed end downwards. Length of air column (l) is measured. Vertical height h of Hg is noted. The pressure inside the tube = H + h.


(c) Slanting Position (Closed end downwards)


The quill tube is then placed in a slanting position with the closed end downwards, Then length of air column (l) is measured. Vertical height h of Hg is noted. The pressure inside the tube = H + h.


(d) Vertical Position (Closed end upwards)


The quill tube is now held vertically with the closed end up. The length of air column (l) is measured. The vertical height 'h' of Hg is noted. The pressure inside the tube = H-h.


(e) Slanting Position (Closed end upwards)


The quill tube is then placed in a slanting position with the closed end up. The length of air column and vertical height ‘h’ of Hg is noted. The pressure inside the tube = H-h.

 

In each case P x l = constant, verifies Boyle’s law. A graph between h and 1/l is found to be a straight line.

 

Observation and Readings

 

Atmospheric pressure H = 76 cm of Hg


Plot P-1/l graph

 

Result:


P x l = constant, verifies Boyle’s law.

Magnetic field lines around a Bar Magnet Experiment

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Experiment - 1


Mapping of Magnetic Field – I (North pole pointing south)

Aim: To map the magnetic lines of force around a bar magnet placed along the magnetic meridian with north pole pointing south and hence to find the moment and pole strength of the magnet.

 

Apparatus: Bar magnet, compass needle, drawing board, paper, pin etc

 

Principle:


Field along the axis of the magnet is given by B = µ0/4π . 2md/(d2-l2)2

Where, µ0 = 4π x 10-7 H/m

m = Dipole moment of the magnet

l = Half the length of the magnet

d = Half the distance between the null points

When north pole pointing south, neutral points are along the axial line of the magnet. At the neutral points (null points) the field due to the magnet is equal and opposite to the horizontal component of earth’s magnetic field (Bh).

ie, B = Bh

Therefore m = Bh(d2-l2)2 107/2d

Polestrength, P = m/2l

 

Procedure:


A sheet of paper is fixed on a horizontal drawing board using pins such that the plane of the paper is exactly parallel to the plane of the board. A line is drawn through the centre of the paper. The magnet and all magnetic materials are removed from the drawing board. A compass needle is placed with its centre on the line at the centre of the paper. The drawing board is rotated till the magnetic needle becomes parallel to the line. Then the line is in the magnetic meridian. The outline of the drawing board is drawn on the table using a piece of chalk. The board should be kept undisturbed throughout the experiment.


The north and south directions are marked on the paper. The bar magnet is placed symmetrically with its axis along the magnetic meridian and north pole pointing south. The outline of the magnet is also drawn on the paper. A dot is marked near to the north pole of the magnet. The compass needle is placed with its south pole above this point and the position of the north pole of the needle is again marked This is repeated till the compass needle reaches the south pole of the magnet .The dots are joined by a smooth curve This gives a magnetic line of force. A number of lines of force are drawn like this as shown in the figure. The directions of the lines of force from north pole to south pole are marked by marking arrow heads.


To locate the neutral points, the compass needle is moved slowly along the axial line. At the null points the needle just begins to rotate. The trace of the needle is taken. The distance (2d) between the null points and the length of the magnet (2l) are measured. Knowing Bh, the moment and the polestrength of the magnet can be calculated.

 

Observations and Calculations

 

Length of the magnet, 2l = ____cm

Therefore l = ____ x 10-2 m

Distance between null points, 2d = ____cm

Therefore d = ____ x 10-2 m

Horizontal component of earth’s magnetic field, Bh = 0.38 x 10-4T

Dipole moment, m = Bh(d2-l2)2 107/2d = _____A-m2

Pole strength of the magnet, P = m/2l = _____ A-m

 

Results


i. The combined magnetic field earth and magnet is plotted and the neutral points are located.

ii. The dipole moment of the magnet = ______ A-m2

iii. The pole strength of the magnet = ______ A-m

 

MODEL VIVA VOCE QUESTIONS AND ANSWERS

 

1. Define pole strength of a magnet. What is its unit?

Pole strength is the force experienced by a magnetic pole when it is placed on uniform magnetic field of unit intensity. Its unit is ampere-metre (A —m).

 

2. Define magnetic dipole moment.

The strength of the magnetic dipole is given by dipole moment. The dipole moment is a vector quantity whose magnitude is equal to the product of pole strength and length of the magnet. It is directed from south pole to north pole.

 

3. Define magnetic meridian.

It is a vertical plane passing through the magnetic axis of a freely suspended magnet at rest.

 

4. What is a neutral point?

In the magnetic field of a magnet, a neutral point is that point, where the field due to the magnet is completely cancelled by the horizontal component of earth's magnetic field.

 

5. How many neutral points are there for a magnet along its axial line when its north pole pointing south?

Two

 

6. How many neutral points are there for a magnet on its equatorial plane when its north pole pointing north?

Infinite number

 

7. What is a magnetic field?

The space around the magnet is called a magnetic field.

 

8. Define one tesla.

A magnetic field B is said to be of intensity I tesla if a charge of IC, moving with a speed of 1 ms-1 at right angles to the field, experiences a force of IN.

 

9. What are poles?

The regions of maximum magnetism in a magnet are called poles.

 

Experiment – 2


Mapping of Magnetic Field – II (North pole pointing North)

Aim: To map the magnetic field around a bar magnet placed with its axis in the magnetic meridian and with its north pole pointing north and hence to determine its magnetic moment and pole strength.

 

Apparatus: Bar magnet, compass needle, drawing board, sheet of paper etc.

 

Principle:


The magnetic field at a point on the equatorial line of bar magnet is given by B = µ0/4π . m/(d2+l2)3/2

Where, µ0 = 4π x 10-7 H/m

m = Dipole moment of the magnet

l = Half the length of the magnet

d = Half the distance between the null points

 

In this case the null points are on the equatorial line of the magnet. At the neutral points the field due to the magnet (B) and the earth’s horizontal component of magnetic field (Bh) are equal and opposite.

ie, B = Bh

Therefore, m =  Bh (d2+l2)3/2 x 107

Pole strength, P = m/2l

 

Procedure

 

A sheet of paper is fixed on a horizontal drawing board. Two mutually perpendicular lines are drawn through the centre of the paper. The magnet and all magnetic materials are kept away from the drawing board. A compass needle is placed with its centre at the centre of the paper. The drawing board is roated till the magnetic needle becomes parallel in one of the lines. Then this line is in the magnetic meridian and the other equatorial line. The outline of the drawing board is marked on the table using a piece of chalk. The board should be kept undisturbed throughout the experiment.

 

The north and south directions are marked on the paper. A bar magnet is placed at the centre of the paper with its axis along the magnetic meridian and the north pole pointing north. The outline of the magnet is drawn. A point is marked near the north pole of the magnet. The compass needle is placed with its south pole coinciding this point and the position of the north pole of the needle is marked. This process is repeated till the compass needle reaches the south pole of the magnet or the end of the paper. These dots are joined by a smooth curve which gives a line of force. Similarly a number of lines of force are drawn like this to get a general form as shown in the figure.

 

To locate the null points, the compass needle is slowly moved along the equatorial line. At the neutral points, the needle just begins to rotate. These places are marked. The distance (2d) between the null points and the length (2l) of the magnet are measured. Assuming the value of the horizontal component of earth's magnetic field (Bh), the value of dipole moment and pole strength can be calculated.

 

Observations and Calculations

 

Length of the magnet, 2l = ____cm

Therefore l = ____ x 10-2 m

Distance between null points, 2d = ____cm

Therefore d = ____ x 10-2 m

Horizontal component of earth’s magnetic field, Bh = 0.38 x 10-4T

Moment of the magnet, m = Bh(d2+l2)3/2 x 107 = _____A-m2

Pole strength of the magnet, P = m/2l = _____ A-m

 

Results


i. The combined magnetic field of earth and magnet is plotted and the neutral points are located.

ii. Dipole moment of the magnet = _____ A-m2

iii. Pole strength of the magnet = _____ A-m

 

MODEL VIVA VOCE QUESTIONS AND ANSWERS

 

1. Two magnetic lines of force will never intersect.Why?

If they intersect at a point, then the field has two directions at that point, which is impossible.

 

2. The magnetic length of a magnet is smaller than its geometric length. Why?

The poles of a magnet are not situated at the ends of the magnet but a little inside it. Thus the magnetic length, which is the distance between the two poles, will be less than its geometric length.

 

3. What is meant by a magnetic field?

Magnetic field is the space around a magnet or the space around a current carrying conductor in which magnetic influence can be experienced.

 

4. Define magnetic field intensity.

It is the force experienced by a unit north pole placed at that point.

 

5. What is meant by uniform magnetic field?

A same force acts in the same direction of force as a unit of north pole is called uniform magnetic field.


6. Define neutral point.

Neutral point is that point in the region of the magnetic field of a magnet, at which the magnetic field intensities of the earth and the magnet have equal magnitudes and opposite direction. (The resultant magnetic field intensity is zero at a neutral point.)

 

7. Define magnetic lines of force.

The path along which the compass needles are aligned is known as magnetic line of force.

 

8. Why direction of magnetic line of force is from a north pole towards a south pole?

Because a free unit north pole (test pole) will move away from a north pole and towards a south pole.

 

9. Why does the magnetic compass needle suddenly reverse direction as it crosses the neutral point region?

Before neutral region, field of magnet is stronger. After neutral region, field of earth is stronger. So the direction of the resultant magnetic field becomes reverse. Hence magnetic compass needle suddenly reverse direction as it crosses the neutral point region.

Refractive Index of Prism Experiment (Class 12)

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The Refractive Index of Prism Experiment using Spectrometer

Aim: To determine refractive index of the material of the prism using spectrometer.

 

Apparatus: Spectrometer, Prism, Sodium vapour lamp etc.

 

Principle:

  

The refractive index of the material of the prism,

Where, A - Angle of the prism

D - Angle of minimum deviation

 

Procedure:

 

i. Preliminary Adjustments

 

The telescope is turned towards a white wall and the eye piece is pushed in or out to get a clear image of the cross wire. The telescope is then focused to a distant object. The distance between the eye piece and objective is adjusted by means of the screw to get a clear image of the distant object. The rays from the distant object will be parallel through the telescope.

 

A monochromatic source of light like sodium vapour lamp is used to illuminate the slit. The telescope is brought in a line with the collimator and the source of the light so that an yellow patch of light is seen through it whose width may be adjusted by adjusting the width of the slit. The distance between the slit and the lens of the collimator is adjusted by means of the screw to get clear image of the slit. Leveling of the prism table can be done by a spirit level.

 

ii. To find the angle of the prism (A)

 

The least count of the spectrometer is found out. The prism is mounted on the prism table with its grounded surface towards the clamp and with its edge (A) turned towards the collimator (fig). The vernier table is clamped. The telescope is rotated till the image of the slit reflected from the face AB is obtained. The telescope is fixed using the radial screw. By working the tangential screw with vertical cross wire is made to coincide with the image. The readings on the main scale and verniers are recorded. The telescope is released and turned to observe the reflected image from the face AC. As before, the readings are recorded. The difference between these two readings on the same vernier is 2A. Thus the angle of prism (A) is calculated.

 

iii. To find the angle of minimum deviation (D)

 

The prism table is rotated so as to have the edge of the prism turned away from the collimator. Turning the telescope towards the base of the prism, the refracted image is observed. The vernier table is slowly rotated in the direction, which will reduce the angle of deviation, following the image with the telescope. At a particular position, the images is found to remain stationary for a moment and then begins to move in the opposite direction. The position at which the image just turns back is the minimum deviation position. The vernier table and telescope are fixed. The vertical cross wire is made to coincide with the image by adjusting the tangential screw of the telescope. The readings on the scale and the verniers are taken. The prism is removed and the telescope is brought in a line with the collimator. By adjusting the tangential screw the vertical cross wire is made to coincide with the direct image. The readings are again taken. The differences between these two readings give D, the angle of minimum deviation. 


Then the refractive index of the material of the prism is calculated using the formula,

Observations and Readings:

 

Magnitude of 1 m.s.d = _______

No: of divisions on the Vernier, N = _______

Least Count (L.C.) = 1 m.s.d/N = _______

 

i. To find the angle of prism (A)

 

Vernier I

Vernier II

MSR

VSR

Total = MSR + VSR x LC

MSR

VSR

Total = MSR + VSR x LC

degree

division

degree

degree

division

degree

Image reflected from face AB (i)

 

 

 

 

 

 

Image reflected from face AC (ii)

 

 

 

 

 

 

Difference b/w (i) and (ii). 2A

 

 

 

 

 

 

 

Mean 2A =____

A = ____

 

ii. To find the angle of minimum deviation (D)

 

Vernier I

Vernier II

MSR

VSR

Total = MSR + VSR x LC

MSR

VSR

Total = MSR + VSR x LC

degree

division

degree

degree

division

degree

Reading of refracted omage (i)

 

 

 

 

 

 

Direct reading (ii)

 

 

 

 

 

 

Difference b/w (i) and (ii). D

 

 

 

 

 

 

 

Mean D = ______ degree

n = _____


Result:

 

Refractive index of the material of the prism =   ________

 

Spectrometer Experiment Viva Questions and Answers

 

1. What is refraction of light?


The phenomenon of the bending of light from its straight path at the surface of two different optical media is called refraction of light.

 

2. What are the laws of refraction?


(a) The incident ray, the normal to the point of incidence and the refracted ray are in the same plane.

(b) The ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant for any two given media. It is also called Snell’s law.

 

3. What is the unit of refractive index?


It has no unit since it is the ratio of two similar quantities.

 

4. What happens, when a prism is set in minimum deviation position?


(a) The angle of emergence becomes equal to the angle of incidence.

(b) The refracted ray travels parallel to the base of the prism.

 

5. What are the uses of a spectrometer?


To find the refractive index and dispersive power, to study spectrum, to find unknown wavelength etc.