Physics labwork

- Set the amplification (7) to a medium level. Observe and make a conclusion of the reception 
of a signal. 
2.3 Investigation of screening and absorption of microwaves 
- Set up the transmitter (9) and receiver (17) facing one another. 
- Place the reflection plate (12) (electrical conductor) between the transmitter and receiver as 
shown in Fig. 5. 
Fig.5. Experimental setup for investigation 2.3 
- Set the amplification (7) to a medium level. Observe and make a conclusion of the reception 
of a signal. 
- Replace the reflection plate with the absorption one (15). Observe and make a conclusion of 
the reception of a signal. 
2.4 Investigation of reflection of microwaves 
- Set up the transmitter (9) and receiver (17) at an angle of incidence to be read off. 
- Line up the reflector plate at angle of approximately 30° with the help of the pointer for the 
rails, which points in the direction of the normal (a line perpendicular to the mirror’s 
surface).as shown in Fig. 6. 
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Fig.6. Experimental setup for investigation 2.4 
- Change the angle of the long rail until the maximum reception is attained. Measure angles of 
incidence from the normal (arrow) and make conclusion. 
- Repeat the procedure with other angles of reflector, that is, 40°, 50° and 60°. 
2.5 Investigation of refraction of microwaves 
- Set up the accessories including transmitter (9), receiver (17), and the prism (10) into the 
side facing away from the arrow as shown in Fig. 7. 
Fig.7. Experimental setup for investigation 2.5 
- Turn the long rail until the maximum reception is attained. Observe and make a conclusion 
of the reception of a signal. 
2.6 Investigation of diffraction of microwaves 
- Set up the accessories including transmitter (9) and receiver (17) directly facing each other 
about 80 cm apart as shown in Fig. 8a. Turn the receiver around on its rail so that it is out of 
the bundled microwave beam and the signal is clearly weakened. 
- Place single-slit plate (14) (width of slit is smaller than the wavelength) so that it is 
vertically aligned about 20 cm in front of the transmitter in such a way that the receiver once 
more detects a signal. 
- Observe and make a conclusion of the reception of a signal if microwaves were diffracted by 
the slit that wavelets could be detected in the shadow of the aperture. 
- Clamp the cover plate (13) in the holder on the hinge plate and set up the transmitter about 
20 cm in front of the plate as shown Fig. 8b. 
- Move the probe (19) in a horizontal plane behind the plate. Observe and record the 
corresponding signal on multimeter. Conclude the experimental results especially when the 
probe is in the shadow of the plate. 
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(a) (b) 
Fig.8. Experimental setup for investigation 2.6 
2.7 Investigation of interference of microwaves 
- Clamp the plate with the double slit (14) centrally in the holder on the plate over the hinge. 
Position the transmitter about 12 cm in front of the plate. Place the receiver probe which is 
connected to a multimeter, about 6 cm behind the double slit plate as shown in Fig. 9. 
Fig.9. Experimental setup for investigation 2.7 
- Move the receiver probe parallel to the double slit plate as illustrated in Fig. 9. Observe and 
record the number of interference maxima corresponding to the signal on the digital 
multimeter. Conclude the experimental results. 
2.8 Investigation of polarization of microwaves 
- Set up the polarisation grating (16) in the screen holder. 
- Check the reception when the polarization grating is aligned horizontally and vertically as 
illustrated in Fig.10a. Make the conclusions of receiver’s signal and explanations of 
experimental results in two cases. 
- Check the reception when the polarization grating is introduced into the beam and tilted by 
45° as shown in Fig.10b. Make the conclusions of receiver’s signal and explanations of 
experimental results. 
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 (a) (b) 
Fig.10. Experimental setup for investigation 2.8 
2.9 Determining wavelength of standing waves 
- Set up the transmitter and reflector plate facing each other about 50 cm apart (in this case the 
angle of incidence 0°) as shown in Fig. 11. The transmitted and reflected waves are 
superimposed, resulting in a standing wave such that the wavelength corresponds to two time 
the distance between two adjacent minima (or maxima), i.e., λ = 2a. 
Fig.11. Experimental setup for investigation 2.9 
- Step 1: roughly investigate the maxima and minima interference of the transmitted and 
reflected wave by moving the microwave probe (19) on the surface of and along the long 
bench as illustrated in Fig.11. 
- Step 2: Placing the probe at the position corresponding to the interference maxima (or may 
be minima) by observing the display on the voltmeter and record that position as x1. After that 
continue to move the probe to the adjacent position of interference maxima (or minima) and 
record that position as x2. Consequently, determine the difference between two these position 
as d. 
- Step 3: Repeat Step 2 for more two times and record the measurement results by making a 
data table with 4 columns as Trial, x1, x2, and d, respectively. 
3. LAB REPORT 
Your Lab report must include 
- investigation results of part 2.1 to 2.8 together with illustrated pictures and conclusions; 
- calculate the wavelength λ = 2d. and frequency of the microwaves and their uncertainty 
using the formula c = λ f., where c = 3x108 m/s. 
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Experiment 6 
Determination of specific heat ratio of air 
based on Clement Desorme's method 
Equipment and Materials: 
1. Large glass bottle or flask; 
2. U-shape water manometer; 
3. Rubber-air-ball blower; 
4. Gas valves; 
5. Support stand. 
Objective 
To determine the specific heat ratio 
 γ = Cp/Cv for air. 
1. BACKROUND 
 A method of determining gamma, the ratio of 
the specific heat capacities at constant pressure 
and constant volume of an ideal gas was 
proposed by Clement Desormes. The method 
consists of a large flask A and an U-shape water 
manometer as shown in Fig.1. In this case air is 
considered to be the ideal gas that would 
undergo a quasi-static adiabatic expansion from 
state 1 to state 2, followed by a constant volume 
process from state 2 to state 3 as illustrated in 
Fig.2. 
 Indeed, when the flask is closed, a mass of dry 
air of volume Vo at atmospheric pressure Po (as 
indicated a zero height difference on the 
manometer) is enclosed. When air is slowly 
pumped into the flask by squeezing the rubber-
air-ball blower B, an additional volume which 
had been outside the flask is now compressed 
inside the flask. The pressure in the flask is 
increased to P1 and the volume the gas occupied 
is reduced to V1. 
The manometer now indicates a height 
difference which is related to the pressure 
change: 
 P1 = Po + ρg H (1)
ρ is the density of the liquid in the manometer. 
When the lid K2 of the flask is quickly opened 
and closed, the extra air is allowed to escape and 
the pressure returns momentarily to atmospheric. 
The ideal gas is allowed to expand adiabatically 
G
B
H 1 
1 
2 M
A 
Fig.1. Clement Desorme’s experiment 
Fig.2. P-V diagram of thermodynamic processes 
occurred in Clement Desorme’s experiment 
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then at this moment the pressure P2 = Po, T2 is less than To and the volume is V2. Since PVγ = const 
along an adiabatic process, then 
P1 V1γ = P2 V2γ (2) 
After just some minutes, gas is warmed up slowly at constant volume, that is T3 = To, V3 = V2, and 
the pressure has increased to P3. 
The new pressure P3 is given by: 
P3 = Po + ρ g h (3) 
Since PV = consst along an isotherm: 
 Po Vo = P1 V1 = P3 V3 (4) 
 Where V2 = V3, the volume of the flask Combining equations (2) and (4) and taking the natural log 
of both sides we obtain: (Hint: divide (2) by P2 which equals Po and find the ratio of pressures to 
volumes from equation (4).) 
ln(P1/ Po) = γ ln(P1/P3) (5) 
In terms of the variables measure in lab, then we have: 
 ln[1 + (ρg H /Po)] = γ {ln[1 + ( ρg H /Po)] - ln[1 + ( ρg h /Po)]} (6) 
If ρg h /Po is small compared to one, then we can make an approximation. When x << 1, we have 
ln(1+x) ~ x. Then equation (6) becomes: 
H ~ γ (H - h) (7) 
Or γ can be simply determined by equation: 
 .
hH
H
−=γ (8) 
2. Measurement Procedure 
- Step 1: Open a valve to the rubber-air-ball blower then performing pump on it to the flask A. 
 Close that valve and wait for the stability of the water columns of the U-shape manometer. 
- Step 2: Adjust the height difference of the two water column of the U-shape manometer H so that 
its value is between 240 to 250 mmH2O. 
- Step 3: Open anther valve to let the air out of the flask. In this step please observe carefully the 
level of two water columns. When they have the same height then must close the valve at once. 
- Step 4: Waite a while (about 5 min) for the stability of the two water column. In this situation, it 
means that the temperature inside and outside of the flask is equal. Record the positions of water 
levels in pipes as l1 and l2 in the U shape manometer and consequently the value h showing their 
difference. 
- Step 5: Repeat the measurement procedure from step 1 to step 4 again for more 9 times and record 
all the experimental results in a data table which consists of 4 columns as Trial, l1, l2, and h, 
respectively. Note that the value of H must be kept constant for all trials of measurement. 
3. LAB REPORT 
Your lab report must consist of 
• a data table showing the measurement results; 
• calculation of the value of gamma using the eq.8 and its uncertainty; 
• comparison of the obtained value from experimental results with that one calculated by using 
the equation
i
i 2+=γ where i = 5 is the Degree of Freedom (DOF) of ideal gas (in this case it 
is air). Make the comments and discussions on the results. 
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