Focal Length of lenses, physics homework help

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Name Section Date 38 LABORATORY 38 Oscilloscope Measurements PRE LABORATORY ASSIGNMENT 1. Describe the components that make up the electron gun in a cathode-ray tube. 2. Describe the voltage waveform that produces a linear time scale when applied to the horizontal plates of a cathode-ray tube. 3. When the electron beam strikes the fluorescent screen, the phosphor glow that results has persistence Approximately how long does the glow persist? 4. A function generator outputs a sine wave off = 200 Hz. It is input to an oscilloscope set at 1 ms/DIV. How many complete cycles of the sine wave are displayed on the oscilloscope? (Hint-The period of the sine wave T is related to the frequency f of the wave by T=1/f, and there are 10 divisions on the time display of the oscilloscope.) COPYRIGHT © 2008 Thomson Brooks Cole 385 386 Physics Laboratory Manual Loyd 5. A typical student oscilloscope on its least sensitive calibrated scale can display a voltage up to a maximum of approximately (a) 1 V (b) 5 V (c) 20 V (d) 200 V. 6. A typical student oscilloscope on its most sensitive calibrated scale can display a voltage down to a minimum of approximately (a) 1 mV (b) 5 mV (c) 20 V (d) 200 mV. 7. A sawtooth wave with a period of 100 ms is applied to an oscilloscope with a screen 10 cm wide. What time is represented by 1 cm on the screen? Data Table 1 Lens Focal Length (a) A Image Distance (cm) 11 22 B 1.-22 p(cm) q(cm) 20 25 30 19 40 16.5 50 15.2 af 3.33584915476 %Diff 37.9021 14.99 fe(cm) 25 11.63 11.68 11.66 9 (p=0) 8.5 р 9 faB p&q 9 31 faep= 8.5 FAB 7.735 fAB theo 7.33 %Diff 5.3767 6.97 (p=) 11.5 FBCP P. 25.5 9 20 Fec p&q FBC fc -59.23 11.5 11.21 11.35 420 Physics Laboratory Manual Loyd SAMPLE CALCULATIONS 1. f- pp P+ 2. PAR = FAB +)/2 = 3. AB theo (18)/(A + B) = 4. fc=(fb)(f)/(f8-fc) = QUESTIONS 1. Why is it not possible to form a real image with lens Calone? 2. Take lens between your thumb and index finger. Is it thinner or thicker at the center of the lens than at the edge? Take lens B between your thumb and index finger. Is it thinner or thicker at the center of the lens than at the edge? From this information alone, what can you conclude about lenses C and B? 3. Consider the percentage difference between the two measurements of the focal length of lens B. Express or as a percentage off. Is the percentage difference between the two measurements less than the percentage standard error? 4. Compare the agreement between the experimental and theoretical values of fas the focal length of lenses A and B combined. Do these data suggest that Equation 4 is a valid model for the equivalent focal length of two lenses in contact? 5. If lens A and lens were used in contact, could they produce a real image? State clearly the basis for your answer. You will need to do a calculation,
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Explanation & Answer

Kindly see attached the requested file containing:- Answer to the prelab questions for the oscilloscope lab- Revised data with the correct calculations. I've also corrected table 1 since you had clearly exchanged the data for the two lenses by comparing the results in the rest of tables- Answer to the postlab questions for the focal lenses labAdditionally, I have included a plagiarism report in case you need to present it. In that case, though, I would suggest you to change the question into private to ensure that your teacher cannot trace you back here.

PHYSICS LABORATORY REPORT
(Name)
(Course)
(Date)

Laboratory 38: Oscilloscope measurements
1.
An electron gun or electron emitter is the source of electrons in the cathode ray tube. Basically, it
is formed of three different components:
-

-

The cathode, from which electrons are emitted. This cathode differs from any other type
of cathode as the ones commonly used in electrochemistry in that emission of electrons
happens as a consequence of the high temperature of the cathode. Taking this into
account, the cathode is generally referred to as a “hot cathode” or “thermoionic cathode”.
The anode, towards which the electrons emitted by the cathode will be directed.
A series of electrical plates that will help in focusing the electron beam emitted from the
cathode. In the case of the cathode ray tube, these set of plates is commonly referred to
as “Wehnelt cylinder”.

2.
In order to obtain a linear timescale in the oscilloscope, we will need to apply a linear wave at the
horizontal plates of the cathode ray tube. However, and since it will be a wave despite of being
linear, the practical shape will be as follows:
-

At t = 0 ms, the voltage will be equal to 0
At t = T ms, the voltage will be equal to the maximum desired voltage VT
For t  (0, T), the voltage will linearly increase from 0 to VT.
Immediately after t = T, the voltage will instantaneously go back to 0 and the next wave
will start.

Taking this voltage pattern into account, we would obtain a voltage waveform as the one
represented in the image:

3.

Generally, the lifetime of the phosphorescence excited electronic state ranges from 1 μs to 10 s
and this time depends on the phosphorescent compound responsible from the emission of the
phosphorescence radiation.
The process by which the phosphor glow appears is during the emission of phosphorescence when
the electronically excited material present in the fluorescent screen relaxes back to the ground
electronic state. Taking into account that it has been excited by the electron beam that has
stricken the fluorescent screen and that as long as it is striking it the phosphorescence signal will
be constant (since new atoms are continuously being excited and relaxed through the emission of
phosphorescence radiation), I expect that the phosphor glow will last until around 10 seconds
after the electron beam has stopped striking the fluorescent screen of the CRT.

4.
The number of complete cycles that will be shown in the oscilloscope is c...


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