GATE Technical: Common Data Questions questions with solutions

Q1. Consider the following C code segment. int a, b, c = 0; void prtFun(void); main() { static int a = 1; /* Line 1 */ prtFun(); a += 1; prtFun(); printf(" %d %d ", a, b); } void prtFun(void) { static int a = 2; /* Line 2 */ int b = 1; a += ++b; printf(" %d %d ", a, b); } What output will be generated by the given code segment?

1. 3 1 4 1 4 2
2. 4 2 6 1 6 1
3. 4 2 6 2 2 0
4. 3 1 5 2 5 2

Answer: 4 2 6 2 2 0

In prtFun, static a starts 2: first call ++b=2, a=4 -> '4 2'; second call a=6 -> '6 2'. In main the local static a=1 becomes 2 after a+=1, and global b is still 0, printing '2 0'. Output is 4 2 / 6 2 / 2 0.

Q2. Common Data for Questions 71,72,73: A three phase squirrel cage induction motor has a starting current of seven times the full load current and full load slip of 5%. If an autotransformer is used for reduced voltage starting to provide 1.5 per unit starting torque, the autotransformer ratio (%) should be

1. 57.77%
2. 72.56%
3. 78.25%
4. 81.33%

Answer: 78.25%

Using Tst/Tfl = x^2 (Isc/Ifl)^2 * sfl with Isc/Ifl=7, sfl=0.05: 1.5 = x^2 * 49 * 0.05 = 2.45 x^2, so x^2=0.6122 and x=0.7825. The autotransformer ratio is 78.25%, not 72.56%.

Q3. Common Data for Questions 74, 75: A 1:1 Pulse Transformer (PT) is used to trigger the SCR in the adjacent figure. The SCR is rated at 1.5 kV, 250 A with I_L = 250 mA, I_H = 150 mA, and I_Gmax = 150 mA, I_Gmin = 100 mA. The SCR is connected to an inductive load, where L = 150 mH in series with a small resistance and the supply voltage is 200V dc. The forward drops of all transistors/diodes and gate-cathode junction during ON state are 1.0 V. The resistance R should be

1. 4.7 kΩ
2. 470 Ω
3. 47 Ω
4. 4.7 Ω

Answer: 470 Ω

The correct option is 470 Ω because it ensures that the gate current falls within the specified range for triggering the SCR, allowing it to operate effectively with the given supply voltage and load characteristics.

Q4. Common Data for Questions 48 and 49: In an experimental set-up, air flows between two stations P and Q adiabatically. The direction of flow depends on pressure and temperature conditions at P and Q. The conditions at station P are 150 kPa and 350 K. The temperature at station Q is 300 K. The following are the properties and relations pertaining to air: Specific heat at constant pressure, cₚ = 1.005 kJ/kgK; Specific heat at constant volume, c_v = 0.718 kJ/kgK; Characteristic gas constant, R = 0.287 kJ/kgK. Enthalpy, h = cₚ T. Internal energy, u = c_v T. Q.48 If the air has to flow from station P to station Q, the maximum possible value of pressure in kPa at station Q is close to

1. 50
2. 87
3. 128
4. 150

Answer: 87

The maximum possible pressure at station Q can be determined using the adiabatic process equations, which relate temperature and pressure. Given the temperature drop from P to Q, the pressure at Q must be lower than at P, and calculations show that the maximum achievable pressure at Q, considering the temperature conditions, is approximately 87 kPa.