TABLE 2 Tip of P3 Potential (V) r’ for =90 r’ for =180 r’ for =270 Average r & r
ID: 2079235 • Letter: T
Question
TABLE 2
Tip of P3
Potential (V)
r’ for =90
r’ for =180
r’ for =270
Average r & r’
(r=1.5, =0)
6.25
1.60
1.70
1.50
1.58
(r=1.7, =0)
5.31
1.70
1.70
1.80
1.73
(r=1.9, =0)
4.29
2.00
2.00
2.00
1.98
(r=2.1, =0)
3.58
2.20
2.30
2.10
2.18
(r=2.3, =0)
2.67
2.50
2.40
2.40
2.40
(r=2.5, =0)
1.94
2.70
2.60
2.50
2.58
Table 1 values represent potential vs distance while Table 2 values are my equipotential lines. In the lab, we are instructed to do this:
Use the average r coordinate (last column in Table 2) and this equation V(r)=Vb + constant (C) times ln(r/rb) to calculate each corresponding potential. We are then supposed to compare them with the values in Table 1.
ra is the radius of the larger ring while rb is the radius of the smaller ring in this lab, while the constant is to be calculated using the equation C=(Va-Vb)/ln(ra/rb). Where I am struggling is which values to use for each equation. What numbers do I use for each Va,Vb,ra,rb? And is the constant supposed to be different for each equipotential line based on V and r? Which average r value do I use for each calculation, the one for the larger ring or the smaller ring? Since there are 5 V values in Table 1 but 6 in Table 2, which one do I leave out?
I hope this question is not too confusing. My physics class is algebra-based so no calculus-based calculations are needed. Thank you!
Tip of P3
Potential (V)
r’ for =90
r’ for =180
r’ for =270
Average r & r’
(r=1.5, =0)
6.25
1.60
1.70
1.50
1.58
(r=1.7, =0)
5.31
1.70
1.70
1.80
1.73
(r=1.9, =0)
4.29
2.00
2.00
2.00
1.98
(r=2.1, =0)
3.58
2.20
2.30
2.10
2.18
(r=2.3, =0)
2.67
2.50
2.40
2.40
2.40
(r=2.5, =0)
1.94
2.70
2.60
2.50
2.58
terminal of the DC power supply and gently place its tip on the outer (bigger) ring (the 12-V ring). Note: the tips of Pl and P2 should be under the water surface and do not move the two rings again. Figure 2 displays only part of the circular graph paper (not to scale) Use the polar coordinates (r, Note: the labels 2, 4, and 6 in Figure 2 refer to the diameters (2r) of 2, 4, and 6 inches, and the unit for the rcoordinate is inch. Connect P2 to the positive lead of Voltmeter B and connect P3 to the negative lead of Voltmeter B. Connect P3 to the positive lead of voltmeter A and connect negative lead of voltmeter A. Note: the sensitivity level of the voltmeters should be set properly. P4 (their tips should be also under the water surface) inside the tray and between the two rings. Ask your TA to check the circuit! 2. Investigate Electric Potential versus-Distance the output voltage of the DC power supply to 12 V. Tum off Voltmeter B, and tum on Voltmeter A Place the tip of probe P3 at point (r-1.5 in, 0 0). Place the tip of probe P4 at points with e-0 and in turn with r 1.7, 1.9. 2.1, 2.3, and 2.5 in. Read the correspondingly potential difference (4) between the P4 and P3 from Voltmeter C. Record them in Table 1 Calculate 4V /(r r) and record the ratio values in Table 1. (Note: 1 inch- 0.0254 m) TABLE 1 r' (inch) Potential difference 4V v) 4V (r-r) VIm) 0.005 0.0 02. 1.9 2.83 18 0152 0.02 O. 0264 3. Map the first equipotential Turn on only Voltmeter B. Move the tip of probe P3 to point (r 1.5, 0 o) Read its potential from Voltmeter B. Mark the point in Figure 2. Record it in Table 2. P4 along e-90° line Turn off voltmeter B. Turn on Voltmeter A, and move the tip probe are place on the same until Voltmeter A reads 0 V. This means that the tips of P3 and P4 equipotential. Read out the y coordinate of the tip of P4 and mark the point in Figure 2. Record it in Table 2. of P4 respectively along the e 180° and 270° Repeat the measurement by moving the tip tip of P4 and lines until Voltmeter A reads 0 V. Read out the corresponding r coordinates of theExplanation / Answer
Question
Where I am struggling is which values to use for each equation. What numbers do I use for each Va,Vb,ra,rb?
Answer
ra - radius of equipotential field (place r' here i.e. the larger ring)
rb - radius of ring used in experiment (place smaller ring here)
Question
is the constant supposed to be different for each equipotential line based on V and r?
Answer
No the constant is a term that wont change
Va=Vb+C*ln(ra/rb) --------------> The varying value of ra will cause C*ln(rb/ra) to become negetive and therefore reduce the value of Va.
Vb is the volatge at which the smaller ring is present and its a constant too. The only valiage in above eqaution is ra.
Question
Which average r value do I use for each calculation, the one for the larger ring or the smaller ring?
Answer
you have to use the value of r' (bigger ring). The purpose of the angle was to measure the value of potential on larger perimeter. So you have to take the value of this avereage and place it in "ra"
Question
Since there are 5 V values in Table 1 but 6 in Table 2, which one do I leave out?
Answer
Since the measurement of r'=1.58 was never made so you can leave it out
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