modern physics

Operation of semiconductor diodes

The demonstration is aimed to understand and analyze silicon diode rectification. The apparatus contains full wave and half wave rectification circuitries. A selection switch is also provided to select between the two circuitries.
An alternating voltage is supplied on the input terminals and the rectified output is observed on the output terminals. The LabView VI provided with the demonstration requires a DAQ card with one analog voltage output, one differential voltage input and one absolute voltage input channels. A sinusoid of amplitude up to 10V and frequency up to 400Hz is supplied through the analog output channel Ao0. The output of the rectifier circuit is received through differential channels Ai0 and Ai4. The output signal is also read back as a reference through the Ai1 input channel. The wiring has to be made according to these requirements for the VI to work.

Coincidence detection circuits for photon correlations

Students Muhammad Ramish Ashraf
Time Frame Spring 2017

Coincidence detection is the simultaneous detection of two or more photons in different detectors. The electronics associated with coincidence-counting tend to be very costly. The aim of this project was to build a small and an affordable circuit based on fast logical AND Gates. The circuit includes a pulse compressor which, depending upon the setting of the multiplexer, can either shorten the input pulse width or let it pass through unchanged. The different available widths that can be obtained are as following:

  • 10 ± 0.2ns
  • 12.8 ± 0.2ns
  • 14.4 ± 0.2ns
  • Original Width  

After the desirable pulse width has been achieved, the output of the pulse compressor is input into a fast (SN74F08) AND gate from which twofold and threefold instances are measured. The circuit comprises of 4 such channels (A, B, C, D) and their complements. The coincidences available are as follows: AB, BC, AC, CD, BD, ABC, ABC.

The project, which was part of Ramish’s independent study was supervised by Dr. Sabieh Anwar and the circuit was built by Mr. Shafique, R.A. spin physics group.


By Azeem Iqbal | Research Stories

Determining the Planck’s constant

Omair1An interesting use of the ubiquitous light bulb is its utility in determining a fundamental constant of quantum mechanics – namely the Planck constant. The purpose of Omair qazi’s experiment was to measure Planck’s constant through the observation of black body radiation. Spectral analysis of the light was carried out verifying Planck’s radiation laws, all using filtered light from a bulb, a spectrometer and photodetectors.

By Azeem Iqbal | Research Stories

Franck Hertz Experiment seen in a new light

The main fFhertzocus of this project was to come up with a new idea regarding the famous Frank-Hertz experiment. The experiment started with observing the well known Franck-Hertz pattern on an oscilloscope. Then the temperature dependence of the curve was demonstrated. We then sought to determine the dependence of he magnetic field on the curve. In order to describe these observations, a mathematical model is being developed.


By Azeem Iqbal | Physics Studio

Magic eye

A magic eye is a simplistic triode tube that was used as a tuning indicator in radio receivers around the time of world-war II. It has a bowl shaped anode coated with a phosphorescent material that produces a green glow when electrons strike on it. This makes possible to measure the curvature of electrons’ trajectory when the tube is placed in a magnetic field. By measuring the radius of curvature, the applied voltage between cathode and anode and the magnetic field, charge-to-mass ratio of the electron can be measured.

By Azeem Iqbal | Modern Physics

Electron diffraction

This interesting demonstration utilizes a highly evacuated electron diffraction tube to show the wave behavior of electrons. The electrons are emitted by the thermionic emission and accelerated towards target by applying a very high potential (2000-5000 V). The target is a micro meshed nickel grid on which a thin layer of graphite is deposited. The electrons being diffracted through the graphite satisfy the Bragg’s condition and produce an interference pattern consisting of two rings.

By Azeem Iqbal | Modern Physics . Solid State Physics

Michelson Interfrometer

This demonstration uses the famous Michelson interferometer which is used either for precise distance measurements or the wavelength of the laser. An assembly of optical components including HeNe laser, mirrors and converging lenses is used. The interference pattern is produced by splitting the beam into two paths using a 50:50 beam splitter. The movable mirror is motor controlled and computer interfaced, a source of changing the path length and produce a interference fringes.

By Azeem Iqbal | Modern Physics . Optics

Statistics of natural radioactivity

The classroom demonstrations uses a gamma ray source of Co-60 placed inside a lead container. The radiation is detected with a Geiger muller tube, whose data is brought into the computer. A histogram is built up showing a Poisson distribution. The distribution of decay times is readily observable and the statistical nature of the phenomenon could be explained.

By Azeem Iqbal | Modern Physics
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