DETERMINATION OF WIRE SPECIFIC RESISTANCE

Task 1. Wire resistance determination

1.1. Set wire length l₁ (set by a teacher) using moving contact.

1.2. Switch on installation. Button «Bridge» must be pushed. Switch button is pushed when scheme of figure 4.1. is used. And switch button is not pushed when scheme of figure 4.2. is used.

1.3. Write down ammeter and voltmeter readings. Enter the measured values of current and voltage into table 1.

Table 1

1.4. Change two times wire length and repeat measurements according to item 1.3.

1.5. Determine wire resistance R₀ setting length l₀ = 0 and repeat measurement according item 3. Enter the results into table 1.

1.6. Determine resistance R_i for each pair of measured U and I according to the formula:

R_і = or R_і = .

Calculate the mean value of resistance R_{i ave} for each wire length l.

1.7. Determine the fractional and absolute ΔR errors of resistance measurement. Enter the results into table 1.

1.8. Determine wire resistance, taking into account wire resistance R₀:

R_i = R_{i ave} – R₀.

Enter the results into table 1.

Task 2. Wire specific resistance determination.

2.1. Measure wire diameter d by micrometer. Enter the results into table 2.

Table 2

Exр. No	rі, Ω×m	rave, Ω×m	Ω×m	Ω×m	Δr, Ω×m	er, %	d, m

2.2. Determine wire specific resistance at different values of l_i according to the formula:

r_i = .

Enter the results into table 2.

2.3. Calculate arithmetic mean value ρ_ave according to the formula:

where n = 3 is amount of calculations.

2.4. Calculate deviation from mean value .

2.5. Calculate root-mean-square deviation according to the formula:

2.6. Determine the absolute error of wire specific resistance measurements according to the formula:

Dr = t_St · .

where the Student’s coefficient is t_St = 4,30 (n = 3 and a = 0,95)

2.7. Calculate fractional error according to the formula

2.8. Write down the result in a form:

= Ω×m.

Conclusions

The data of laboratory work fulfillment

Pass mark Signature

Mark of laboratory work defending Signature

questions to be admitted for doing laboratory work and its defending

1. What factors does specific wire resistance depend on?

2. What factors have no influence on specific resistance value?

3. How can wire specific resistance be obtained?

4. Write down formula for wire specific resistance determination.

5. What is measurement unit of wire specific resistance?

6. What does temperature resistance coefficient equal?

7. Write down formula for dependence of specific resistance on temperature.

8. What is specific conductivity?

9. Write down formula for dependence of specific conductivity on temperature.

10. What are reasons of systematic methodical error of wire resistance measurement? How is systematic methodical error avoided?

11. Deduce formula for determination of fractional error of specific resistance measurement.

12. How is wire resistance determined? How is branch wire resistance taken into account

LABORATORY WORK

Date: 2015-01-12; view: 1226