The Open Door Web Site : IB Physics : Practical Work : Using an Oscilloscope

Most oscilloscopes are "double beam" oscilloscopes. They have two separate inputs. One of the terminals of the supply must be connected to the "earthed" side of the input.

Before starting the experiment, study the controls and find out how to:

...........- change the brightness

...........- "focus" the electron beam

...........- change the horizontal and vertical position of the spot

...........- change the vertical sensitivity of the oscilloscope

...........- change the horizontal speed of the spot.

To measure the maximum (or peak) value of an alternating voltage.

a) Obtain a small spot in the centre of the screen.

b) Connect a low voltage (a.c.) supply to the input.

c) Measure the length of the line. Divide the length by 2, (why?) and calculate the maximum voltage using the "volts cm^-1" (or "volts div^-1") calibration. Do this with the low voltage supply unit set to 6V, 12V and 24V.

	(length of line)/2	Maximum Voltage
6V
12V
24V

The numbers written on the low voltage supply unit are root mean square (r.m.s.) voltages. Use your results to find the relation between the r.m.s. value and the maximum value of an a.c. supply.

v_max = _______________

Estimating the Frequency of the supply

a) Obtain a thin horizontal line on the screen. Make it just bright enough to see clearly.

b) Connect the low voltage supply unit to the input and adjust the controls to give one complete "cycle" of a sine curve on the screen.

c) Using the "time cm^-1" (or "time.div^-1") calibration, find the time for one alternation, T.

N.B. The "time cm^-1" (or "time div^-1") control is called the "time-base" of the scope.

T = ____________

f = 1/T = ____________

Link to Observing the effect of a Diode and a Capacitor

Link to Using an Oscilloscope to compare the frequencies of two supplies of Alternating Voltage