Friday, October 19, 2012

Micrometer, its construction, reading ITI fitter, Std 11

Micrometer (Screw Gauge)

Micrometer screw gauge is a form of calipers used for measuring small dimensions. Screw gauge in extensively used in the engineering field for obtaining precision measurements. The article describes the principle and main parts of a basic micrometer screw gauge.
Micrometer screw gauge (or micrometer caliper) is an instrument or device for measuring the length of an object which is more precise than a ruler and vernier caliper. It because a micrometer screw gauge has the smallest scale of 0.01 mm. The device is widely used in mechanical engineering for measuring small diameter, thickness, or angles to a high degree of accuracy.
More details video : 
Micrometer (Screw Gauge) its construction and How to take reading.
or paste this link :

Construction and Parts
Thus the main parts of a micrometer screw gauge are:

Micrometer Frame

Frame :
Made up of Dropped Forged steel or  Malleable Steel. All other parts joint with frame.

Micrometer Anvil

Anvil :
Most important parts of  Micrometer, which is made up of Alloy steel, hardening, tempering  and finishing is done very accurately. 

Micrometer Spindle

Spindle :
Is made up of Nickel Chrome metal, which is also hardened, Grind and accurately made. Which is move to and fro as we rotate thimble. The maximum displacement of spindle is 25 mm.

Micrometer Measuring faces

Measuring faces :
Both the end of Anvil and Spindle, Measuring face is fixed, which is made from Alloy steel, as well as hardened, grind and accurately finished. 

Micrometer Barrel or Sleeve

Sleeve :
The Barrel or sleeve is connects the frame to the cylindrical tube. It is a non-movable part of the screw gauge and has a scale inscribed over it which is the main scale of the device. Moreover, it also carries the most important part of the micrometer- the screw.

Micrometer Thimble

Thimble :
The thimble or head is the end of the cylindrical tube and is turned to move and adjust the spindle. The thimble carries the Micrometer or secondary scale.

Micrometer Ratchet

Ratchet :
There is one more part called the ratchet which is provided at the end of the tube. The ratchet is kind of limiting device which applies a pressure by slipping at a predetermined torque and thus prevents the spindle from moving further.

Micrometer Spindle lock nut

Screw Lock :
screw gauges also consist of locking devices which holds the scales at a particular position for prevent any kind of error while taking readings.

A screw gauge consists of a “U” shaped metallic structure, which is attached to a hollow cylindrical tube on one end. The hollow tube has a uniformly threaded nut inside it. A long stud with a plane face is fitted into this nut. Exactly on the opposite side of this nut and on the other end of the U shaped frame, a smaller stud with a plane face is also attached. Faces of both the studs are exactly parallel to each other.

This U shaped metallic structure is known as the frame of the micrometer screw gauge. The smaller stud is known as the anvil and the longer one is known as the spindle. The anvil is the fixed part of the device, whereas the spindle moves as and when the head is moved. The frame carries both the anvil and barrel, and is also heavier than the rest of the parts. The object to be measured is held between the anvil and the spindle.

The Barrel or sleeve is connects the frame to the cylindrical tube. It is a non-movable part of the screw gauge and has a scale inscribed over it which is the main scale of the device. Moreover, it also carries the most important part of the micrometer- the screw.

The screw is the heart of the micrometer and is located inside the barrel. The screw converts small dimensions into measurable distance using a scale. The thimble or head is the end of the cylindrical tube and is turned to move and adjust the spindle. The thimble carries the vernier or secondary scale. There is one more part called the ratchet which is provided at the end of the tube. The ratchet is kind of limiting device which applies a pressure by slipping at a predetermined torque and thus prevents the spindle from moving further. Some screw gauges also consist of locking devices which holds the scales at a particular position for prevent any kind of error while taking readings.

A micrometer screw gauge also uses two scales – main and secondary scales. The secondary scale is provided on the thimble and is the measurement of the pitch of the screw. This means that the reading on the secondary scale measures the distance moved by the thimble per rotation. The scale on thimble is divided into 100 equal parts and measures hundredths of a millimeter. The thimble scale rotates over the spindle or the main scale. The main scale is a millimeter scale subdivided into equal parts with half a millimeter distance. When the object is to be measured, it is placed in between the anvil and the spindle. Readings from both the scales are taken into account for arriving at the final measurement.

Micrometer screw gauge is a delicate device and thus special care should be taken while handling it. Moreover, it is also important that the micrometer is well calibrated to prevent any kind of error in the final reading.

Precaution Steps
The spindle and anvil are cleaned with a tissue or cloth, so that any dirt present will not be measured.
The thimble must be tightened until the first click is heard.
The zero error is recorded.
Reading = Reading of main scale + Reading of thimble scale.

While taking a reading, the thimble is turned until the wire is held firmly between the anvil and the spindle.

The least count of the micrometer screw can be calculated using the formula given below:
Use the given formula:
Least Count (L. C) = Pitch/no. of divisions on micrometer barrel(thimble)
Pitch = distance travelled by thimble on linear scale in one rotation.
Least count = 0.01 mm

Types of error in micrometer screw gauge reading

Every micrometer prior to its use should be thoroughly checked for backlash error or zero error.

Backlash error:
Sometimes due to wear and tear of the screw threads, it is observed that reversing the direction of rotation of the thimble, the tip of the screw does not start moving in the opposite direction immediately, but remains stationary for a part of rotation. This is called back lash error.

Zero error:
If on bringing the flat end of the screw in contact with the stud, the zero mark of the circular scale coincides with the zero mark on base line of the main scale, the instrument is said to be free from zero error. Otherwise an error is said to be there. This can be both positive and negative zero error.

Calculating micrometer screw gauge reading:

Total observed reading = main scale reading + (circular scale division coinciding the base line of main scale) x least count

True diameter = observed diameter – zero error

Example, main scale reading = 2mm or 0.2cm

Circular scale reading = 56, so 56 x 0.001 = 0.056cm

So observed reading = 0.2 + 0.056 = 0.256cm

More details view video :

Friday, July 6, 2012

Post office box Experiment for std 8 to 12 Physics

A post office box and other necessary instruments are given to you. Take three appropriate ratios of the resistances in the two arms of Post Office Box and determine the values of two unknown resistances.
Now connect the unknown resistances in series and parallel respectively and verify the laws of series and parallel combinations of resistances.
It works on the principle of balanced Wheatstone bridge.
A Battery,
unknown resistance (Rx & Ry),
Post Office Box, 
a galvanometer, 
connecting wires.
Post Office Box Apparatus
Condition 1 Resistance Rx connect between C and D
Post Box Wiring Diagram find Unknown Resistance Rx 
Condition 2 Resistance Ry connect between C and D
Post Box Wiring Diagram find Unknown Resistance Ry
Post OfficeBox line diagram Series connection Rx and Ry
Series connection of Rx and Ry wiring diagram
Parallel Connection line Diagram of Rx and Ry
Wiring Diagram Parallel connection of Rx and Ry

Series connection, R’s = Rx + Ry + …..Ohm
Parallel connection, R’p = Rx Ry  /  Rx + Ry = ….Ohm.
(1) Unknown resistance, Rx = ….Ohm. , Ry = ….Ohm
Observation for Post Office Box Experiment
Calculation table for Post Office Box

The experimental and theoretical values of equivalent resistance for series and parallel connections are equal,within the experimental error. This implies the validity of the rules for the different combinations of resistances.
 All plug keys of Post Office Box must be tight.
 Contact points of K1 and K2 must be cleaned  with sand paper.
 Galvanometer should be very sensitive.
 Throughout the experiment  press key K2(battery key) first and then key K1(galvanometer key).

More Video : Post Office Box Video presentation.

Post Office Box Experiment.

Friday, March 25, 2011

Ohm's law Experiment presentation with Audio and Video for std 12 Physics

Ohm's Law
AIM :-A voltmeter, a current meter, and an unknown resistance etc. are given to you. Prepare an appropriate circuit to verify Ohm’s law. With appropriate values of current and voltages, only with the help of calculations, determine the value of unknown resistance.
PRINCIPLE : Potential difference in a conductor produces electric current.
A unknown resistance,
a voltmeter (0 - 10 V),
a milliammeter (0 - 500mA), a battery,
a rheostat,
a tap key,
connecting wires.

Sunday, March 20, 2011

Internal Resistance of Primary Cell Experiment Potentiometer for std 12

Internal Resistance of Primary cell With the help of Potentiometer
Internal resistance of primary cell
To find the internal resistance of a primary cell, by calculation and from a graph, with the help of a potentiometer.
It works on the principle of potentiometer.
A potentiometer having a long (~400 cm) resistive wire of uniform cross-section, a battery E of 3 to 4 V, a primary cell ( dry cell or Laclanche cell or a Daniel cell), two rheostats [ 0 – 25 W (Rh1) and 0 – 500 W (Rh2) ], a galvanometer, a R.B.(0 – 50 W), two simple keys and a jockey.
Internal Resistance of Primary Cell Experiment Apparatus
Internal Resistance Of Primary cell wiring diagram experiment
Internal Resistance Of Primary cell Observation table 
Internal Resistance Of Primary cell with graph 
Internal Resistance Of Primary cell Slop Experiment

Internal Resistance of Primary cell With Potentiometer Experiment Video

Copper voltameter Experiment for std 12 Physics with animation Video

AIM :-
Connect given copper voltameter in an appropriate circuit determine the electro chemical equivalent of copper.
On passing electric current through CuSO4 solution, Cu+2 and SO-24 ions are separated or chemical effect of electric current.
A copper voltameter,
6 V battery ( or D.C. Mains),
an ammeter,
a rheostat,
a simple key,
sand paper,
a stop-watch, balance,
weight box, etc.
Copper Voltameter Experiment  Apparatus
The cathode plate should be throughly cleaned after rubbing with sand paper.
Pass only that much current as is obtained from the calculation of the area of the immersed part of the cathode plate.
Use only a fresh solution of CuSo4. To prepare the solution dissolve about 25 g of CuSO4 crystals in 100 cm3 water. Add a few drops of sulphuric acid (H2SO4) to make it more conducting.
Hold the plate from its upper end so as to avoid touching its surface.
Cathode plate should be washed immediately after it is taken out of the solution.
Copper Voltameter  Experiment Line Diagram
Copper Voltameter  Wiring Diagram for Std 12 Experiment
1. To Cathode plate dip in clean water, and wash off all the CuSO4, solution sticking to it. Thereafter wash it again with tap water.
2. Hold it in the sunshine for some time till it dries out. Now find out its mass by Physical balance.

Observation table for Copper Voltameter
Copper Voltameter Experiment Observation Table

Copper Voltameter  Experiment Calculation
Copper Voltameter Experiment presentation Video.

Monday, February 14, 2011

Angle of Prism, Physics practical for the standard 12

Determine with the help of pins, the angle of the given glass prism. Determine the values of angle of emergence and angle of deviation for four different values of angle of incidence. Hence prove that i + e = A +d.
Reflection and refraction of light.
 While marking the position of a prism with pencil, the prism should not be disturbed. 
A prism should be carefully put back exactly at the marked position. 
While pressing the heads of the pins for fixing them use metal coin or a hard object so that you do not hurt your palm. 
Do not press the pins very hard in the board otherwise it becomes difficult to remove them afterwards. 
See that the pins pushed in the board remain perpendicular to the board.
Angle of Prism 

Angle of Prism Conclusion

AIM :-
Using pins with a given prism determine the angles of deviation for six different values of angle of incidence. Draw the graph of angle of deviation versus angle of incidence. Determine, from this the angle of minimum deviation and using following formula determine refractive index of material of the prism.
Angle of Prism Formula

Angle of prism, A = ……. .

Angle of Deviation measure
Angle of Deviation

Angle of Deviation Observation table  

Angle of Deviation Graph

Sunday, January 30, 2011

Spectrometer, Physics Practical for Standard 12

AIM : -
To determine the prism-angle of a given prism.
(Keeping prism-table steady)
A spectrometer, a source of light, a prism, a sprit-level and a magnifying glass. 



Spectrometer Fixed Table

Spectrometr on left

Spectrometr on Right

Spectrometer Observation table

Angle of prism

From the observations of window-X,
            2A = q1q2
                        \A =
From the observations of window-Y,
            2A = q1’  -  q2’
                        \A = 

It measures the color change. That gives the indication of the rate of the light reactions of the photosynthesis in the conditions of the experiment.

Spectroscopy is the study of the interaction between matter and radiated energy. Historically, spectroscopy originated through the study of visible light dispersed according to its wavelength, e.g., by a prism. Later the concept was expanded greatly to comprise any interaction with radiative energy as a function of its wavelength or frequency. Spectroscopic data is often represented by a spectrum, a plot of the response of interest as a function of wavelength or frequency.

Spectrometry and spectrography are terms used to refer to the measurement of radiation intensity as a function of wavelength and are often used to describe experimental spectroscopic methods. Spectral measurement devices are referred to as spectrometers, spectrophotometers, spectrographs or spectral analyzers.

Daily observations of color can be related to spectroscopy. Neon lighting is a direct application of atomic spectroscopy. Neon and other noble gases have characteristic emission colors, and neon lamps use electricity to excite these emissions. Inks, dyes and paints include chemical compounds selected for their spectral characteristics in order to generate specific colors and hues. A commonly encountered molecular spectrum is that of nitrogen dioxide. Gaseous nitrogen dioxide has a characteristic red absorption feature, and this gives air polluted with nitrogen dioxide a reddish brown color. Rayleigh scattering is a spectroscopic scattering phenomenon that accounts for the color of the sky.

Spectroscopic studies were central to the development of quantum mechanics and included Max Planck's explanation of blackbody radiation, Albert Einstein's explanation of the photoelectric effect and Niels Bohr's explanation of atomic structure and spectra. Spectroscopy is used in physical and analytical chemistry because atoms and molecules have unique spectra. These spectra can be interpreted to derive information about the atoms and molecules, and they can also be used to detect, identify and quantify chemicals. Spectroscopy is also used in astronomy and remote sensing. Most research telescopes have spectrographs. The measured spectra are used to determine the chemical composition and physical properties of astronomical objects (such as their temperature and velocity).