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.

(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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