What power source do I need to perform the electrolysis of water? A low-voltage DC power source is needed for the electrolysis ofThe Battery Eliminator Power Supply (AP5375) is a great power supply to use for electrolysis experiments. However, a 6-volt or 9-volt battery will also supply enough electricity to electrolyze water.  Caution:  Do not use an AC power supply for electrolysis experiments.  will produce an explosive mixture of hydrogen and oxygen gas in the tubes of the electrolysis chamber. In 1925, two graduate students, Goudsmit and Uhlenbeck proposed the notion of electron spin, the spin angular momentum, , obeying the same quantization rules as those governing orbital angular momentum of atomic electrons. In particular, in any given direction, say the z-direction, the component, , is : In addition the ‘spinning’ electron possesses a magnetic dipole Here is the Landé g-factor which is very close to 2

As an exercise calculate the magnetic moment of an orbiting point charge and express it in terms of its angular If the electron is placed in a magnetic field, , the magnetic moment will have the potential Combining equations (1), (2) and (3) one obtains: Therefore, ignoring spin-orbit interactions, a given energy level for an atomic electron will be split due to spin into two levels, differing in energy by an amount of: Electron Spin Resonance (ESR) refers to the situation where photons of a frequency are absorbed or emitted during transitions between these two levels and . as a function of and knowing the values of and , the Landé g-factor can be determined. the relationship one obtains: The magnetic field is provided by a pair of Helmholtz coils in a series connection with an AC and a DC power supply (see ). field has an average value, , given by the DC power supply and a superposed AC 60Hz component provided by the AC power

The resulting magnetic field as a function of time is shown in : The average magnetic field can be determined from the current in the coil which is measured by the DC ammeter.split ac units cheap If the distance between the coils is equal to their radius ,10 ton ac package unit then midway between the coils and on their axis the magnetic field isac power supply not recognised where is the number of turns in each coil. across the resistor (see ) is fed to the X-input of an oscilloscope. This causes the trace to sweep horizontally back and forth across the screen at 60 Hz in time with the alternating magnetic field. As the trace passes the center of the screen, we know that the corresponding magnetic induction is

Electrons for this experiment are provided by a sample ofAn unpaired electron in this molecule moves on a highly delocalized orbit so that its orbital contribution to the magnetic moment is negligible. This electron can be viewed as essentially free, only its spin contributing to the magnetic moment. Thus the Landé g-factor for DPPH is very close to that for a free electron. For the typical magnetic fields used in this experiment, photons of frequencies in the range ~25-50 MHz are required for the transitionsThese are provided by a short coil connected to aThe magnetic field of this coil is perpendicular to that provided by the Helmholtz coils, an arrangement that results in a perturbing torque acting on the electron’s spinWhen the oscillator frequency matches the resonance condition, the impedance of the oscillator circuit decreases and theA DC voltage proportional to this current is fed to the Y-input of the oscilloscope.

The Helmholtz coils have 320 turns each and a mean radius of 6.8 cm. Arrange the coils parallel to each other, as shown in , at a mean distance of 6.8 cm apart. should be pointing outwards. Arrange the ESR unit, also shown in , so that the small coil is accurately at the center of the Helmholtz coils. Place the glass tube containing the DPPH inside the small coil. Connect the Helmholtz coils in a series circuit with the AC and the DC power supplies , the ammeter and the resistor as shown in . Use a coaxial cable to feed the voltage across the resistor to the X-input of the oscilloscope. ESR unit and frequency divider as follows (see Fig. 4): Connect the black middle socket of the frequency divider to the black FREQUENCY input socket of the DIGICOUNTER (2nd from right at Connect the yellow output socket of the frequency divider to the “lf” yellow FREQUENCY socket (3rd from right). Connect the red power input socket of the frequency divider to the

red 10 V output socket on the side panel of the DIGICOUNTER. Connect the 12 V AC output of the DIGICOUNTER to the green and black input terminals on the ESR unit. Connect the output of the ESR unit to the “Input” of the frequency divider using a coaxial cable. Connect the output of the ESR unit to the Y-input of the oscilloscope, also using a coaxial cable. On the DIGICOUNTER, set the FUNCTION switch to , the RANGE switch to , slide the switch below FREQUENCY to the left (to ), set the single reading/continuous switch toOn the frequency divider, slide the switch to theSwitch on the DIGICOUNTER and press . DIGICOUNTER will now read the input frequency in MHz with the decimal point in the correct position. Make sure that the direction of the magnetic fields produced by the two Helmholtz coils point in the same direction at the location of the Use the gauss meter and measure the magnetic field at the location of the sample as a function of the current in the

Compare your measurement to the calculated values from (7). Set the X-gain on the oscilloscope to 0.1 V/cm and the coupling to DC. Using the horizontal positioning knob on the scope center the signal on the screen and adjust the AC power supply until the trace is about 8 cm wide. Set the ESR frequency to its minimum value and then position the resonance peak in the center of the scope screen and adjust via the DC power supply until the range in x is exactly symmetric around theRecord the corresponding average coil current. 2 to 3 times and record the result for each setting. range of currents exactly centered around the resonance peak the magnetic field at the average current corresponds to the field where the resonance occurs. Repeat the previous procedure for a total of 6 frequency settings, the last being theRecord the corresponding DC current and determine the corresponding magnetic field. Since there should be a linear