Passion of Physics — Interactive Simulations, Courses & Research

Science Apps: Strobe

Click HERE to download from Google Play Store a wonderful Science App "Strobe".
This Android App turn your smart phone into a full pledged stroboscopic light source.

Strobe App Page

A strobe light can be used in the following ways:

1. You can stop your fan without switching it off and without harming yourself. Yes that sounds crazy but that you can do. All you need is a dark room with a fan revolving in it. Just adjust the frequency of the strobe as accurately as possible to stop the fan. Of course the fan is not stopped, it is still revolving as you can feel from the air flow. But when the blades of your fan rotate by such an angle that one blade replaces the succeeding blade in its' position when the next flash of light comes in, the fan seems to stand still. If you have '$N$' blades equally angled apart(They must be equally angled apart. Why ? Think friend Think), the condition is that,

\[\frac{m}{f_{flash}}=\frac{60}{N\times RPM}\]

Whereas $m$ is an integer ( $m=1,2,3...$ ) and $RPM$ is the Revolutions Per Minute of the fan.
If we rearrange the above equation we get,

\[RPM =\frac{60 \times {f_{flash}}}{m \times N}\]
The rotational speed of the fan in $RPM$!

Jamin Interferometer - A Historical Exhibit @ Harvard University Museum

Credits and Thanks : http://waywiser.fas.harvard.edu/objects/16403/compensator-for-jamintype-interferometer

Jamin Interferometer Schematic

Michelson Interferometer - Determination of thickness of a thin mica sheet

Let the refractive index of mica be 'μ ' and the thickness of the thin sheet be 't'. If the mica sheet is introduced into the path of one of the interfering beams, the optical path length is increased by 2(μ-1)t. If 'n' is the number of fringes shifted in the fringe system then,

2(μ-1)t = nλ ------------------------------------ (1)

But as fringes with monochromatic light are exactly alike, it is not possible to count the number fringes shifted due to the introduction of mica sheet.To overcome this difficulty, localized fringes are formed with a white light source and central dark fringe is made to coincide with the vertical cross wire.The paths AB and AC are then exactly equal.

Localized White Light Fringes
Credit: By Stigmatella aurantiaca at English Wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=20155966

Michelson Interferometer Setup

The mica sheet is then introduced between the glass plate G1 and M1 such that light passes through it normally.Mirror M1 is adjusted till the central dark fringe again coincide with the vertical cross wire of the telescope. The distance 'l ' through which the mirror moved is noted. The white light is now replaced with monochromatic light of wavelength 'λ' .Mirror M1 is moved back and number of fringes 'n' contained in length 'l ' is found out . Then from equation (1),thickness of the mica sheet is given by,

Analog Electronics - 7BPH5C1 - Syllabus

III YEAR – V SEMESTER

COURSE CODE: 7BPH5C1

CORE COURSE IX – ANALOG ELECTRONICS

Unit I SEMICONDUCTOR DIODES AND REGULATED POWER SUPPLIES

Semiconductor – p-n junction diode – rectifiers – half and full wave rectifiers – bridge rectifier – efficiency – ripple factor – R-C and π section filter circuits.

Zener diode – characteristics – voltage regulator – regulated power supply using zener diode.

Unit II TRANSISTORS AND BIASING

Transistor action – CB, CE & CC modes – comparison – amplifier in CE arrangement – load line analysis – cut – off and saturation – Relation between α and β – Transistor biasing - base resistor bias - feedback resistor bias - voltage divider bias – JFET – construction and working - characteristic parameters.

Unit III AMPLIFIERS

Single stage amplifier – Phase reversal – DC & AC equivalent circuits – Voltage gain – Classification of amplifiers – Input impedance of an amplifier - RC, transformer, direct coupled amplifiers – Comparison of different types of amplifiers.

Unit IV OSCILLATORS

Transistor audio power amplifier – Difference between voltage and power amplifiers – Performance quantities of power amplifiers – Classification of power amplifiers – Expression for collector efficiency – Class A amplifier – Push – Pull amplifier.

Feedback principle – Negative and positive feedback – current gain and voltage gain in negative feedback amplifier – Barkhasan condition for oscillation – damped and undamped oscillations –Hartley, Colpitt and phase shift Oscillator.

Unit V OPERATIONAL AMPLIFIER

Characteristics of an ideal op-amp – virtual ground - op-amp biasing – Non-inverting & Inverting amplifiers– Applications of op-amp – adder, subtractor, differentiator, integrator.

op-amp signal generators: Phase shift, Hartley, Square wave and triangular wave generators.

Text Books:

V.K.Mehta, Principles of Electronics, S.Chand & Co Ltd.,10^th Edition, New Delhi, 2007.
R.S.Sedha – Text Book of Applied Electronics, S.Chand & Co Ltd., II Edition, New Delhi, 2004.
Electronic Devices and Circuits – Salivahanan and Suresh Kumar, Mc Graw Hill Edn. New Delhi, 2012

Books for Reference:

B.L. Theraja – Basic Electronics – S. Chand & Co, V Edition, New Delhi, 2009.
Malvino & Leach – Transistor Approximations – International Publication, New Delhi, – 2000.

Optics and Spectroscopy - 7BPH3C1 Syllabus

II YEAR – III SEMESTER

COURSE CODE: 7BPH3C1

CORE COURSE VI – OPTICS AND SPECTROSCOPY

Unit I GEOMETRICAL OPTICS

Lens – Spherical aberration in lenses – Methods of minimizing spherical aberration – chromatic aberration in lenses – condition for achromatism of two thin lenses (in and out of contact) – Coma - Aplanatic lens – Eyepieces – Ramsden’s and Huygens’s eyepieces. Dispersion – Angular and Chromatic dispersion – combination of prisms to produce i)dispersion without deviation ii) deviation without dispersion – Cauchy’s dispersion formula– Direct vision spectroscope – Theory of formation of rainbow.

Unit II INTERFERENCE

Conditions for interference – colours of thin films – Air wedge – theory – determination of diameter of a thin wire by Air wedge – test for optical flatness – Newton’s rings – Determination of refractive index of a liquid. Michelson’s Interferometer – theory and its Application (Measurement of wavelength and difference between wavelength of two close lines, thickness of mica sheet) – Jamin’s interferometers – determination of refractive index of gases

Unit III DIFFRACTION

Fresnel’s diffraction –Rectilinear propagation of light – zone plate –diffraction at circular aperture – opaque circular disc – Fraunhofer diffraction at single slit – Double slit – Plane diffraction grating – theory and experiment to determine wavelength – overlapping of spectral lines. Rayleigh’s criterion for resolution – resolving power – resolving power of grating – resolving power of a prism.

Unit IV POLARISATION

Double refraction – Huygens’s explanation of double refraction in uni axial crystals – Nicol Prism – Nicol Prism as polarizer and analyzer – Polaroids and their uses – Quarter wave plates and Half wave plates. Plane, elliptically and circularly polarized light – Production and detection – Optical activity– Fresnel’s explanation of optical activity – Specific rotatory power – determination using Laurent’s half shade polarimeter.

Unit V SPECTROSCOPY

Microwave and infrared Spectroscopy – Rotation of molecules – Rotational Spectra – The rigid diatomic molecules, selection rules – the intensities of spectral lines – Infrared spectroscopy (outlines only) – Raman Spectroscopy – Quantum theory of Raman effect – Classical theory of Raman effect – Molecular Polarisability – pure rotational Raman spectra of linear molecules – vibrational Raman spectra – Applications.