GATE EE 2010

Question 1
The value of the quantity P, where P=\int_{0}^{1}xe^{x}dx, is equal to
A
0
B
1
C
e
D
1/e
Engineering Mathematics   Calculus
Question 1 Explanation: 
P=\int_{0}^{1}xe^x\; dx
Integrating by parts:
\begin{aligned} \text{Let } \; u&= x,\\ dv&= e^x\; dx\\ du&= dx,\\ v&=\int e^x\; dx=e^x \\ \text{Now, } \int udv&= uv-\int v\; du\\ \therefore \;\;\int x e^x\; dx &=xe^x-\int e^x\; dx \\ &=xe^x-e^x+c \\ \int_{0}^{1} xe^x\; dx&= [xe^x-e^x]_0^1\\ &= (1 \times e^1 -e^1)-(0 \times e^0 -e^0)\\ &= 0-(-1)\\ &= 1 \end{aligned}
Question 2
Divergence of the three-dimensional radial vector field \vec{r} is
A
3
B
1/r
C
(\hat{i}+\hat{j}+\hat{k})
D
3(\hat{i}+\hat{j}+\hat{k})
Engineering Mathematics   Calculus
Question 2 Explanation: 
\begin{aligned} \vec{r} &= x\hat{i}+y\hat{j}+z\hat{k}\\ \text{div } \vec{r}&= \bigtriangledown \cdot \vec{r}\\ &=\left ( \hat{i}\frac{\partial }{\partial x}+\hat{j}\frac{\partial }{\partial y}+\hat{k}\frac{\partial }{\partial z} \right )(x\hat{i}+y\hat{j}+z\hat{k})\\ &=\frac{\partial x}{\partial x}+\frac{\partial y}{\partial y}+\frac{\partial z}{\partial z}\\ &=1+1+1=3 \end{aligned}
Question 3
The period of the signal x(t)=8 sin(0.8 \pi t+ \pi/4) is
A
0.4 \pi s
B
0.8 \pi s
C
1.25 s
D
2.5 s
Engineering Mathematics   Complex Variables
Question 3 Explanation: 
If period = T, then x(t+T)=x(t)
Here, x(t)= 8 \sin(0.8 \pi t+\pi /4)
putting x(t+T)=x(t) we get
8 \sin(0.8\pi (t+T)+\pi /4)=8 \sin (0.8 \pi t+\pi /4)
\sin(0.8\pi (t+T)+\pi /4)= \sin (0.8 \pi t+ \pi /4)
\sin(\theta _1)=\sin(\theta _2)\Rightarrow \theta _1=\theta _2+2 \pi
\therefore \;\; 0.8\pi (t+T)+ \pi /4=0.8 \pi t+ \pi /4+2 \pi
0.8\pi T=2 \pi
T=2.5 s
Question 4
The system represented by the input-output relationship y(t)=\int_{-\infty }^{5t}x(\tau )d\tau , \; t\gt0
A
Linear and causal
B
Linear but not causal
C
Causal but not linear
D
Neither liner nor causal
Signals and Systems   Linear Time Invariant Systems
Question 4 Explanation: 
Integrator is always a linear system.
\begin{aligned} \text{Since, }y(t)&=\int_{-\infty }^{5t}x(\tau )d\tau \;\;t \gt 0 \\ &\text{For t=1,} \\ y(t)&= \int_{-\infty }^{5}x(\tau )d\tau \end{aligned}
here value at t=1 depends on future values like at t=2,3,... of input x(t).
So, it is a noncausal systems.
Question 5
The switch in the circuit has been closed for a long time. It is opened at t = 0. At t =0^+, the current through the 1 \muF capacitor is
A
0A
B
1A
C
1.25A
D
5A
Electric Circuits   Transients and Steady State Response
Question 5 Explanation: 
As the switch has been closed for a long time, the circuit is in steady state. At steadystate, capacitor is open circuit,

Using KVL,
5-I-4I=0 I=1A
V_c(0^-)=4 \times 1=4V
As the voltage across capacitorcan not change abruptly,
So, V_c(0^+)=V_c(0^-)=4V
Circuit at t=0^+

Current through capacitor at t=0^+
I_c(0^+)=\frac{4}{4}=1A
Question 6
The second harmonic component of the periodic waveform given in the figure has an amplitude of
A
0
B
1
C
2/\pi
D
\sqrt{5}
Signals and Systems   Fourier Series
Question 6 Explanation: 
The given signal is odd as wel as having half wave symmetry.
So, it has only sine terms with odd harmonics. So, for second harmonic term amplitude =0.
Question 7
As shown in the figure, a 1 \Omega resistance is connected across a source that has a load line v+i=100. The current through the resistance is
A
25A
B
50A
C
100A
D
200A
Electric Circuits   Basics
Question 7 Explanation: 
A resistor has linear characteristics
i.e. V=Ri
\Rightarrow \;\; V=i
Load line,
V+i=100
i+i=100
current through resistance,
i=\frac{100}{2}=50A
Question 8
A wattmeter is connected as shown in figure. The wattmeter reads.
A
Zero always
B
Total power consumed by Z_1 \; and \; Z_2
C
Power consumed by Z_1
D
Power consumed by Z_2
Electrical and Electronic Measurements   Measurement of Energy and Power
Question 8 Explanation: 


Potential coil draws negligible current. So current through Z_1 and Z_2 is same.
current through current coil =I_{cc}=I
Voltage across potential coil =V_{pc}
Voltage across Z_1=V_{pc}=V
Wattmeter reads power consumed by Z_2, as voltage across potential coil = Voltage across Z_2
Current through current coil = Current through Z_2.
Question 9
An ammeter has a current range of 0-5 A, and its internal resistance is 0.2 \Omega. In order to change the range to 0-25 A, we need to add a resistance of
A
0.8 \Omega in series with the meter
B
1.0 \Omega in series with the meter
C
0.04 \Omega in parallel with the meter
D
0.05 \Omega in parallel with the meter
Electrical and Electronic Measurements   Galvanometers, Voltmeters and Ammeters
Question 9 Explanation: 
To extend the range of ammeter, a resistance R_{sh} is connected across the meter.

I_m= full scale deflection current=5A
I=25A
Multiplying power =m=\frac{I}{I_m}=\frac{25}{5}=5
I_m=\frac{IR_{sh}}{R_{sh}+R_m}
\frac{I}{I_m}=\frac{R_{sh}+R_m}{R_{sh}}
m=1+\frac{R_m}{R_{sh}}
R_{sh}=\frac{R_m}{m-1}=\frac{0.2}{5-1}=0.05
Question 10
As shown in the figure, a negative feedback system has an amplifier of gain 100 with \pm10% tolerance in the forward path, and an attenuator of value 9/100 in the feedback path. The overall system gain is approximately :
A
10\pm 1%
B
10\pm 2%
C
10\pm 5%
D
10\pm 10%
Control Systems   Feedback Characteristics of Control Systems
Question 10 Explanation: 
G=100\pm 10%
\frac{\Delta G}{G}=10% or 0.1
H=\frac{9}{100}
Overall gain,
T=\frac{G}{1+GH}
T=\frac{100}{1+100 \times \frac{9}{100}}=10
Sensitivity w.r.t. 'G'=\frac{1}{1+GH} \times 10%
\;\;\;=\frac{1}{1+10 \times 1}\times 10%
\;\;\;=\frac{10}{11}\cong 1%
There are 10 questions to complete.
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