Question { 1657 }

ELECTRICAL TECHNOLOGY - EXAMPLE 16.1 : According to Shockley equation, the I - V characteristic of a diode is approximated by I = IS [ exp (nVD / VT) - 1 ]. For silicon, let the reverse bias saturation current IS as 0.000000000001. If n is ideality factor with value of 1.5, VT as thermal voltage drop of 0.026 V at room temperature, what is the value of current I that passes through the silicon diode in the heater of evaporator when the forward voltage drop VD = 0.026 V? Please take note that exp is the exponential function with e(1) = 2.718, e(2) = 7.389.

Answer

ELECTRICAL TECHNOLOGY - ANSWER 16.1 : I = IS [ exp (nVD / VT) - 1 ] = 0.000000000001 [ exp (1.5 x 0.026 / 0.026) - 1 ] = 0.00000000000348 A. The answer is given by Kang Chuen Tat; PO Box 6263, Dandenong, Victoria VIC 3175, Australia; SMS +61405421706; chuentat@hotmail.com; http://kangchuentat.wordpress.com.

Question { 1419 }

ELECTRICAL TECHNOLOGY - EXAMPLE 16.2 : In a selection of suitable heating equipment for drying of crystals of biochemical, the one of the lowest current consumption will be chosen for safety consideration. Selection is available : (A) 120 V microwave oven 1800 W. (B) 240 V conventional oven 11000 W. Which one should be chosen and why?

Answer

ELECTRICAL TECHNOLOGY - ANSWER 16.2 : For (A), AMPS = WATTS / VOLTS = 1800 / 120 = 15. For (B), AMPS = 11000 / 240 = 45.83. Dryer (A) should be chosen as less current is consumed. The answer is given by Kang Chuen Tat; PO Box 6263, Dandenong, Victoria VIC 3175, Australia; SMS +61405421706; chuentat@hotmail.com; http://kangchuentat.wordpress.com.

Question { 1768 }

COMPUTER PROGRAMMING FOR ENGINEERS - EXAMPLE 17.1 : By using Excel or other easiest programming package, explain how I, the integral of sin x dx from 0 to 3.142 could be approximated using random number. Find the exact value of I.

Answer

COMPUTER PROGRAMMING FOR ENGINEERS - ANSWER 17.1 : When Excel is used, let column A=RAND() and column B=ASIN(A1). Stretch the columns A and B vertically. The data is transferred to Word, then reinserted into column C and D in order to prevent changes in column A. By using the sort function from the lowest to highest, arrange the data in column C and D, followed by trapezoidal rule performance in column E=0.5*(C1+C2)*(D2-D1). The 2 times summation of values in column E will approximate I gradually as the random numbers used increase. Exact value of I = -2(-1) = 2 units. The answer is given by Kang Chuen Tat; PO Box 6263, Dandenong, Victoria VIC 3175, Australia; SMS +61405421706; chuentat@hotmail.com; http://kangchuentat.wordpress.com.

Question { 1736 }

ELECTRICAL TECHNOLOGY - EXAMPLE 16.3 : In the design of a solar power system steps of calculations below are followed : (a) The power output of the inverter of the solar panel is 100 watts. What is the power input, Pin to the inverter when the efficiency of the inverter is 50 %? (b) If the rated power of the inverter is 300 watts, how many inverter is needed for the solar panel? (c) Charge controller of V = 12 volts is used to supply power to the inverter. What is the input current I to the inverter? (d) If the charge controller capacity is 10 A, how many charge controllers are needed? (e) If a biochemical mixer consumes 100 watts, running for 2 hours per day, what is the energy consumption in kilowatt hour per day? (f) What is the input energy needed when the efficiency of the inverter is 50 %? (g) If your area receives 2.88 hours of full sunlight per day, how much energy, in kilowatt hour can be produced per day when one solar panel can produce 20 watts of power? (h) If you know that you have to produce total energy as the answer for (f), how many solar panels are needed? (i) Each V = 12 V battery has 5 ampere hours. If the total energy needed is in answer (f), then how many batteries are needed to run the biochemical mixer if without sunlight for 3 days?

Answer

ELECTRICAL TECHNOLOGY - ANSWER 16.3 : (a) Input = Output / Efficiency = 100 watts / 0.5 = 200 watts. (b) Number of inverter = Input / Rated power = 200 / 300 = 2 / 3 < 1. Practically only 1 inverter is needed. (c) I = Pin / V = 200 / 12 = 16.667 A. (d) Number of charge controllers = Input / Rated current = 16.667 / 10 = 1.6667 < 2. Practically only 2 are needed. (e) Energy consumption = 0.1 kilowatt x 2 hours / day = 0.2 kilowatt hour per day. (f) Input energy = Energy consumption / Efficiency = 0.2 / 0.5 = 0.4 kilowatt hour per day. (g) Energy generation per day per solar panel = 2.88 hours x 0.02 kilowatt = 0.0576 kilowatt hour. (h) Number of solar panels needed = Answer for (f) / Answer for (g) = 0.4 / 0.0576 = 6.944 < 7. Practically only 7 are needed. (i) Ampere hour per day to run the load = 0.4 kilowatt hour per day / 12 V = 1 / 30 k. Total ampere hour needed for 3 days = 1 / 30 k x 3 = 0.1 k. Number of batteries needed = 0.1 k / 5 = 100 / 5 = 20. The answer is given by Kang Chuen Tat; PO Box 6263, Dandenong, Victoria VIC 3175, Australia; SMS +61405421706; chuentat@hotmail.com; http://kangchuentat.wordpress.com.

Question { 2178 }

Question 104 - In photoelectrical effect analysis of quantum chemistry, let E = kinetic energy of electron, p = intensity of UV light, f = frequency of UV light. According to Classical Theory, E = c for all values of f, E = mp. According to Quantum Theory, E = c for all values of p, E = mf + c. In a graph, m and c are constants where m is slope and c is y intercept. If m = 2 and c = 3 with similar value of E : (a) find the value of p according to Classical Theory; (b) find the value of f according to Quantum Theory.

Answer

Answer 104 - (a) E = c = 3, then E = mp = 2p = 3, then p = 3 / 2. (b) E = c = 3, then E = mf + c = 2f + 3 = 3, then f = (3 - 3) / 2 = 0. The answer is given by Kang Chuen Tat; PO Box 6263, Dandenong, Victoria VIC 3175, Australia; SMS +61405421706; chuentat@hotmail.com; http://kangchuentat.wordpress.com.

Question { 1386 }

COMPUTER PROGRAMMING FOR ENGINEERS - EXAMPLE 17.2 : There are 5 simultaneous equations with 5 unknowns as follow : 16 V - 4 X - Z = 36, 4 X - 4 W - Y + Z = 3, 8 V + 4 W - X + Y = 10, X - W = 1, V + W = 0. Find the values of V, W, X, Y and Z accurately within 15 minutes. State the computer program that you use to get the answers.

Answer

COMPUTER PROGRAMMING FOR ENGINEERS - ANSWER 17.2 : Quick computer programming will produce V = 2, W = -2, X = -1, Y = 1, Z = 0. Computer program used = Excel 2013. The answer is given by Kang Chuen Tat; PO Box 6263, Dandenong, Victoria VIC 3175, Australia; SMS +61405421706; chuentat@hotmail.com; http://kangchuentat.wordpress.com.

Question { 1632 }

COMPUTER PROGRAMMING FOR ENGINEERS - EXAMPLE 17.3 : (a) The byte is the basic building block of computer data used in chemical engineering process simulation where 16 bits make a word, 4 bits make a nibble, 32 bits make a quad word and 8 bits make a byte. Then how many nibbles are there in a megabytes? (b) In computer data items, let : 1 bit - counts from 0 to 1, 8 bits - counts from 0 to 255, 16 bits - counts from 0 to A. What is the value of A? (c) In a binary system of 4 bits, if 1100 = 12, 1101 = 13, 1110 = 14, 1111 = 15, B = 16, then guess the value of B. (d) By using any form of tools, find the exact value of 2 power 64 or 2^64.

Answer

COMPUTER PROGRAMMING FOR ENGINEERS - ANSWER 17.3 : (a) 4 bits as a nibble, then 8 bits as 2 nibbles and as a byte. Finally a megabytes make 2 meganibbles. (b) By induction, final number of count = 2 power (number of bit) - 1. For 16 bits, A = 2 power 16 - 1 = 65536 - 1 = 65535. (c) Undetermined and no answer for B since 1111 = 15 is maximum in a binary system of 4 bits. (d) By using web calculator, 2^64 = 18446744073709551616. The answer is given by Kang Chuen Tat; PO Box 6263, Dandenong, Victoria VIC 3175, Australia; SMS +61405421706; chuentat@hotmail.com; http://kangchuentat.wordpress.com.

Question { 1866 }

ENGINEERING DRAWING - EXAMPLE 18.1 : For a Vernier scale of representative fraction (RF) = 1 / 25, calculate the length of the scale for the reading up to 4 metres.

Answer

ENGINEERING DRAWING - ANSWER 18.1 : Length of the scale = RF x maximum length of the scale = 1 / 25 x 4 x 100 = 16 cm. The answer is given by Kang Chuen Tat; PO Box 6263, Dandenong, Victoria VIC 3175, Australia; SMS +61405421706; chuentat@hotmail.com; http://kangchuentat.wordpress.com.

Question { 1460 }

ENGINEERING DRAWING - EXAMPLE 18.2 : For a Vernier scale that consists of 0.11 cm per section, estimate the length on actual standard ruler of 0.1 cm per section for 2.39 m and 0.91 m.

Answer

ENGINEERING DRAWING - ANSWER 18.2 : For 2.39 m, length on standard ruler = 2.39 - 0.99 = 1.4 m. For 0.91 m, length on standard ruler = 0.91 - 0.11 = 0.8 m. The second decimal numbers for both Vernier scale and standard scale should be the same. The answer is given by Kang Chuen Tat; PO Box 6263, Dandenong, Victoria VIC 3175, Australia; SMS +61405421706; chuentat@hotmail.com; http://kangchuentat.wordpress.com.

Question { 1540 }

Question 106 - In a wavefunction, let P(x) = A cos kx + B sin kx. By using the boundary conditions of x = 0 and x = l, where P(0) = P(l) = 0, prove by mathematical calculation that P(x) = B sin (npx / l) where p = 22 / 7 approximately, n is a rounded number. A, B and k are constants.

Answer

Answer 106 - When x = 0, P(0) = A cos (k x 0) + B sin (k x 0) = A = 0. When x = l, P(l) = A cos (k x l) + B sin (k x l) = 0 = B sin (k x l), then k x l = arc sin 0 = np, k = np / l. Finally P(x) = B sin kx = B sin (npx / l) as proven. The answer is given by Kang Chuen Tat; PO Box 6263, Dandenong, Victoria VIC 3175, Australia; SMS +61405421706; chuentat@hotmail.com; http://kangchuentat.wordpress.com.

Question { 1812 }

ENGINEERING DRAWING - EXAMPLE 18.3 : Autocad computer program is used to draw a pipe that is used to transport natural gases for processing. Actual length of the pipe is 10 metres. The pipe has cross sectional area of circle in shape with measured circumference of s = 3 metres. (a) If 10 units are used to represent the actual length of the pipe in computerised engineering drawing, find the diameter of the pipe, d that will be shown in the engineering drawing. (b) If one unit in the program equals to 1 centimetre, find the scale used in the computer program.

Answer

ENGINEERING DRAWING - ANSWER 18.3 : (a) s = 3.142 d, then d = s / 3.142 = 3 / 3.142 = 0.9548 metres. Since 10 units : 10 metres, then d = 0.9548 units. (b) 1 unit : 1 metre or 1 centimetre : 1 metre for engineering drawing : actual object, then 0.01 m : 1 m or 1 : 100 is the scale used. The answer is given by Kang Chuen Tat; PO Box 6263, Dandenong, Victoria VIC 3175, Australia; SMS +61405421706; chuentat@hotmail.com; http://kangchuentat.wordpress.com.

Question { 1515 }

ENGINEERING NUMERICAL METHODS - EXAMPLE 19.1 : Solve the simultaneous equation using simple Excel program : r + s - t = 7, 2r - s = 0, 3r + 2t = 15. Explain the use of functions of MINVERSE and MMULT together with the keyboard C (Ctrl) + S (Shift) + E (Enter).

Answer

ENGINEERING NUMERICAL METHODS - ANSWER 19.1 : By using Microsoft Excel, r = 3.22, s = 6.44, t = 2.67. MINVERSE, or =minverse is used to inverse the 3 x 3 matrix with constants of r, s, t. MMULT, or =mmult can be used to obtain the answers by functions (inversed matrix of 3 x 3, constants of 7 and 0 and 15). CSE is an Excel function to perform quick calculations for the cells. The answer is given by Kang Chuen Tat; PO Box 6263, Dandenong, Victoria VIC 3175, Australia; SMS +61405421706; chuentat@hotmail.com; http://kangchuentat.wordpress.com.

Question { 1667 }

ENGINEERING NUMERICAL METHODS - EXAMPLE 19.2 : For a mixture of benzene (B), toluene (T) and xylene (X), the equation applies where x for B, T and X will sum up to 1. The equation of x for each component is x = (L / V + 1) (F) / (L / V + K). The data of F for each component are : 0.5 for B, 0.35 for T, 0.15 for X. The data of K for each component are : 1.98 for B, 0.76 for T, 0.24 for X. When x for B + x for T + x for X = 1, find the values of (a) L / V; (b) x for each component of B, T, X respectively. You may use Excel program - Data : What-If-Analysis for Goal Seek to perform the iterative calculations.

Answer

ENGINEERING NUMERICAL METHODS - ANSWER 19.2 : By using Excel program, L / V = 0.654. The data of x are : 0.31 for B, 0.41 for T, 0.28 for X. You may bring your own calculator on laptop or phone with Excel program to assist the trial and error. The answer is given by Kang Chuen Tat; PO Box 6263, Dandenong, Victoria VIC 3175, Australia; SMS +61405421706; chuentat@hotmail.com; http://kangchuentat.wordpress.com.

Question { 1971 }

ENGINEERING NUMERICAL METHODS - EXAMPLE 19.3 : There are 2 simultaneous equations : (A1) x + (B1) y = D1 and (A2) x + (B2) y = D2. (a) By using Excel program, find the values of x and y when A1 = 80, A2 = 150, B1 = 52, B2 = 100, D1 = 3.5 and D2 = 2.3. (b) Write the expression of Excel in the form of =MMULT(MINVERSE(W:X),Y:Z) in order to get the values of x and y. W, X, Y and Z may be A1, A2, B1, B2, D1 and D2.

Answer

ENGINEERING NUMERICAL METHODS - ANSWER 19.3 : (a) Excel program will produce the answers of x = 0.025, y = 0.01. (b) =MMULT(MINVERSE(A1:B2),D1:D2). The answer is given by Kang Chuen Tat; PO Box 6263, Dandenong, Victoria VIC 3175, Australia; SMS +61405421706; chuentat@hotmail.com; http://kangchuentat.wordpress.com.

Question { 1427 }

DIFFERENTIAL EQUATIONS - EXAMPLE 20.1 : By using Excel program either on laptop or desktop PC, solve the differential equation dy / dx = -2y + x + 4 with h = 0.005, initial values : x = 0, y = 1. The 4th order Runge-Kutta method provides : y(N + 1) = y(N) + (1/6) (k1 + 2k2 +2k3 + k4), k1 = h [ -2y(N) + x(N) + 4 ], k2 = h { -2 [ y(N) + k1 / 2 ] + x(N) + h / 2 + 4 }, k3 = h { -2 [ y(N) + k2 / 2 ] + x(N) + h / 2 + 4 }, k4 = h { -2 [ y(N) + k3 ] + x(N) + h + 4 }. What is the value of y at x = 0.5?

Answer

DIFFERENTIAL EQUATIONS - ANSWER 20.1 : Programming method will provide y = 1.709 when x = 0.5. The answer is given by Kang Chuen Tat; PO Box 6263, Dandenong, Victoria VIC 3175, Australia; SMS +61405421706; chuentat@hotmail.com; http://kangchuentat.wordpress.com.