Physics Lab 212P 10 The Oscilloscope AC Circuits NAME LAB PARTNERS LAB SECTION LAB INSTRUCTOR DATE EMAIL ADDRESS Physics Lab 212P 10 Software List Science Workshop Microsoft Excel Equipment List all items marked with are in the student kit others are supplied at the time of the lab RLC circuit board Oscilloscope cable Science Workshop Interface voltage probes Connecting wires with alligator clips Two 1 5 V batteries in holder Lab Activity The Oscilloscope and AC Circuits The oscilloscope is an extremely useful instrument for measuring electrical signals that vary with time The conventional oscilloscope is essentially like a TV set it consists of an electron gun that accelerates a beam of electrons towards a phosphor screen say along the z direction The beam is deflected in the x y plane by two sets of plates that provide an electric field To measure a voltage that varies in a regular manner with time we provide a periodic voltage to the x plates that sweeps the electron beam from one side of the phosphor screen to the other when it reaches the far right side the beam snaps back to its starting position Then we provide the measured voltage to the y plates so that the electron beam goes up and down depending on the supplied voltage In this lab you are provided with a Tektronix 2213 oscilloscope The front panel of this instrument is divided up into six areas To the far left is the cathode ray tube CRT display The next vertical strip contains 6 items including the power button The next two areas contain controls related to the vertical deflection of the electron beam Channel 1 and Channel 2 The last two areas on the right contain controls for the horizontal deflection of the electron beam including a time base control for determining the rate at which the electron beam will sweep across the display and the trigger controls for timing this sweep Before turning the power on check that the following knobs are in the indicated positions 1 Auto intensity turn counterclockwise fully 2 The three position knobs Channel 1 channel 2 and horizontal pointing up 3 Vertical mode switches Channel 1 4 Horizontal mode switch no dly no delay 5 Sec Div 2 ms 2 millisecond cm 6 Trigger mode Auto Now push the power switch on Turn the Auto Intensity switch slowly counter clockwise You should see a line appear on the screen Keep the intensity at the minimum level required for you to clearly see the line Prolonged operation at very high intensities can damage the phosphor screen If you do not see a line Check whether the scope is plugged in If the scope is plugged in push the beam find button briefly This should show you that the beam is being deflected in a particularly direction but is off the screen You can bring the beam back by using the position knobs Exercise 1 Using the oscilloscope as a DC voltmeter Your scope should already have a co axial cable connected to the Ch 1 input The red connecting wire will be connected to the positive end of any voltage you want to measure while the black connecting wire will be connected to the negative ground terminal In general it is important to keep to this convention to avoid potentially serious short circuits Note the red knob that is part of the CH 1 Volts div control knob Gently turn this red knob back and forth to get a feel for how it works Then turn it clockwise as far as it will go and make sure that it clicks in place The Channel 1 input is now calibrated so that the numbers on the volts div scale are meaningful Anytime you use a scope always check that the different scale knobs are in the calibrated position Connect the red and black ends of the cable to each other to provide a clear input of 0 V Adjust the Ch 1 controls as follows Position adjust this so that the horizontal line is in the center of the display Volts div set this to 1 on the 1X side left side of the dial This means that every vertical displacement of 1 cm major division on the display scale corresponds to 1 V AC GND DC switch for CH 1 set this at DC Now connect a 1 5 V battery across the scope input with the black connector to the negative terminal and the red connector to the positive terminal Note down the vertical deflection of the display line Try to set the volts div dial to a value that will give you the most accurate reading Repeat the above with the two batteries in series Q1 Write down the readings you obtained above Single battery Volts Div Vertical deflection cm Voltage V Two batteries in series Volts Div Vertical deflection cm Voltage V Exercise 2 Using the oscilloscope to measure the amplitude and frequency of a periodic voltage signal Now it s time to learn how the scope can be used to measure a voltage signal that varies with time We ll be using a signal that is provided by the Science Workshop interface box First make sure that there is a pair of wires that are connected to the Science Workshop interface box at the output banana plug outlets extreme right Connect the scope leads to the output leads from the interface box making sure you connect the black lead to ground and the red one to the positive output Set the scope CH 1 VOLTS DIV controls to measure 1 V div Set the Sec div knob to 5 ms Make sure the central red knob is in the calibrated position Start Science Workshop and click on the Sample V icon A window will open up that allows you to select an output waveform with given amplitude volts and frequency Hertz Set the amplitude to 1 Volt and the frequency to 100 Hz Select the sine wave icon Click the on button Observe the oscilloscope display You should see a sine wave Discuss amongst your group how the pattern on the screen is quantitatively related to the frequency of the input signal Try turning the sec div knob to different values and observe how the display changes Try varying the frequency of the Science Workshop output signal from 30 Hz to 300 Hz Observe how the oscilloscope display changes and use the sec div knob to keep the display at a convenient scale Q2 Suppose you want to measure the frequency of an input signal using the scope Describe how you would go about doing this i e write down an equation that relates frequency f the setting on the sec div scale and the period of the sine wave as observed on the horizontal scale Exercise 3 Using the oscilloscope to analyze a series R L C circuit Now for a real circuit measurement This will involve some concepts that you are probably still covering concurrently in the lectures and recitations so we will only