ME108 1/ 5

SCHOOL OF ENGINEERING

MODULAR HONOURS DEGREE COURSE

LEVEL 2

SEMESTER 2

1999/2000

EXPERIMENTAL METHODS

EXAMINER : D KENNAIRD

Answer all questions Time allowed : 2 hours

Total number of questions = 3

All questions carry equal marks.

The figures in brackets indicate the relative weightings of parts of a question.

Log Books and Experimental Methods Briefs will be allowed into the test.

Special requirements : Graph paper.

1)

a)Describe with the aid of diagrams how a sample of 60/40 brass may be prepared for microscope examination (un-etched sample). You should explain how certain procedures help to preserve the specimen for examination. (20)

b)The slides are examined under an optical microscope. Describe the purpose of the microscope and its limitations. (5)

c)What is a micrograph? Sketch a micrograph of an un-etched polished longitudinal section of brass (you should include appropriate labelling). (5)

2)

a)An experiment is undertaken to establish the relationships of Poisuelle (equation 1) and Blasius (equation 2). Describe (with the aid of equations) how the velocity of the water in the working section is determined. How can errors in the calculation of velocity be kept to minimum? (15)

b)Explain how the transition from laminar to turbulent flow is observed, and how the viscosity of the water is determined? (5)

c)Using the sample set of values of Reynolds numbers and Friction factors (for turbulent flow, table 1) calculate the value of the constant and Reynolds number indices for a relationship of the form suggested in equation 3. (10)

(Equation 1)

(Equation 2)

(Equation 3

Reynolds Number / Friction Factor
2050 / 0.008120146
2300 / 0.007844615
2500 / 0.00765082
3000 / 0.007243586
3500 / 0.006916232
4000 / 0.006644648
4150 / 0.006571667
4700 / 0.00633083
5000 / 0.006214397

Table 1. Values of experimental data for question 2 c

3)

a)Describe with the aid of diagrams how a Digital Volt Meter (DVM) may be used to measure current through the resistor, and the voltage across the resistor in the circuit described in figure 1. What basic checks to the DVM should be carried out before operation and how can the DVM be used to check a diode. (7)

b)An A.C. supply is connected to the circuit in figure 2, with the aid of diagrams show how the voltage waveform across the diode can be viewed and measured. Describe how the equipment used to measure the waveform should be configured. (10)

c)Sketch the waveform observed for the procedure undertaken in (b), labelling the waveform appropriately (3)

d)Four diodes are used to full wave rectify the output of an ac transformer, sketch the arrangements of diodes labelling both the input and output rails. Sketch the waveform observed. (5)

e)A capacitor is placed across the output of the full wave rectifier how does this effect the waveform observed. (5)

Figure 1. D.C. circuit

Figure 2. A.C. Circuit