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DFCCIL’21 EE: Daily Practice Quiz. 09-September-2021

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EXAM DATES: 26 SEPT TO 30 SEPT

               DFCCIL’21 EE: Daily Practices Quiz 09-Sep-2021

Each question carries 1 mark.
Negative marking: 1/4 mark
Total Questions: 06
Time: 08 min.

Q1. The ratio of the mobility to the diffusion coefficient in a semi-conductor has the unit of:
(a) V×s
(b) cm×V^(-1)
(c) V×cm^(-1)
(d) V^(-1)

Q2. A tunnel diode is
(a) An amplifying device
(b) High resistivity p-n junction diode
(c) A very heavily doped p-n junction diode
(d) A slow switching device

Q3. A silicon PN junction is forward biased with a constant current at room temperature. When the temperature is increased by 10⁰C, the forward bias voltage across the PN junction:
(a) Increases by 25 mV
(b) Decreases by 25 mV
(c) Increases by 60 mV
(d) Decreases by 60 mV

Q4. In PMMC instruments, damping torque is provided by:
(a) Eddy currents
(b) Air friction
(c) Fluid friction
(d) Thermal effect

Q5. In 3-phase induction motor the mechanical power developed in terms of air-gap power(P_ag) is:
(a) (1-s) Pag
(b) (s-1) Pag
(c) Pag/((1-s))
(d) Pag/s

Q6. Determine the current through the 5Ω resistor in the figure given below utilizing Thevenin’s theorem.

DFCCIL 2021, DFCCIL 2021. DFCCIL ELECTRICAL QUIZ, DFCCIL EXAM DATES, DFCCIL ELECTRICAL EXECUTIVE |_30.1

(a) 2A
(b) 3A
(c) 0A
(d) 1A

SOLUTIONS
S1. Ans.(d)
Sol. Relation between diffusion constant(D) and mobility(µ): D α µ ⇒D=V_Tµ
Where; V_T= thermal voltage
∵ µ/D=1/VT
Unit: V^(-1)

S2. Ans.(c)
Sol. A tunnel diode is a very heavily doped p-n junction diode which is used as very high-speed switching device.

S3. Ans.(b)
Sol. dV/dT=-2.5 mV/⁰C
For 10⁰C increased temperature, voltage across PN junction will decrease by 25 mV.

S4. Ans.(a)
Sol. In PMMC instruments, damping torque is provided by eddy currents.

S5. Ans.(a)
Sol. For 3-phase induction motor: P_mech=(1-s) P_ag

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