GE 6252 BASIC ELECTRICAL AND ELECTRONICS ENGINEERING
UNIT 1 ELECTRICAL CIRCUITS AND MEASUREMENTS
TWO MARK QUESTIONS & ANSWERS
Question 1: State Ohm’s law.
Answer: At constant temperature, the potential difference across the two ends of a conductor is directly proportional to the flow of current in the conductor.
V α I
V = I R
Where, V – voltage (potential difference) in volts
I – current in amperes
R – Resistance in ohms.
Question 2: What are the limitations of Ohm’s law?
Answer: The limitations of Ohm's law are,
1. Ohm’s law does not apply to non-metallic conductors.
2. Ohm’s law does not apply to non-linear devices.
3. Ohm’s law is true at constant temperature.
Question 3: State Kirchoff’s voltage law.
Answer:
Kirchoff’s voltage law: In any closed circuit or mesh or loop, the algebraic sum of all the voltage taken around is zero.
A rise in potential (going from positive to negative terminal of a source) is assumed positive. A fall in potential (going from negative to positive terminal of a source) is assumed negative.
Question 4: State Kirchoff’s current law.
Answer:
Kirchoff’s current law: The algebraic sum of currents meeting at a junction or node in an electrical circuit is zero.
The current flowing towards a junction is assumed positive. The current flowing away from a junction is assumed negative.
Question 5: Two resistances with values 6Ω and 3Ω are connected in parallel. The combination is in series with 8Ω. Find the equivalent resistance.
Given: Rp1 = 6Ω; Rp2 = 3Ω; Rs = 8Ω
Formulae: Resistance in series, Rs = Rs1 + Rs2
Resistance in parallel, 1/Rp = 1/Rp1 + 1/Rp2
Solution: 6Ω and 3Ω are in parallel connection.
Equivalent parallel resistance, 1/Rp = 1/6 + 1/3
1/Rp = ½
Rp = 2Ω
This 2Ω is in series with 8Ω.
Total equivalent resistance, Req = Rp + Rs
Req = 2 + 8
Req = 10 Ω
Answer: Req = 10 Ω.
Question 6: A 120Ω resistor has a specified maximum power dissipation of 1 W. Calculate maximum current level.
Given: R = 120Ω; P = 1 W
Formula: P = I2R
Solution: I2 = P/R
I2 = 1/120
I2 = 0.00833
I = √0.00833
I = 0.0912 A or I = 91.2 mA.
Answer: I = 91.2 mA.
Question 7: A sinusoidal current wave is given by i = 50 sin (100πt). Determine the root mean square value.
Given: sinusoidal current wave, i = 50 sin (100πt).
Formulae: Form of current wave, i = im sin wt
RMS value, irms = 0.707 im.
Solution: Here, irms = 0.707 im
irms = 0.707 * 50
irms = 35.35 A
Answer: irms = 35.35 A
Question 8: A sine wave has a peak value of 12 V. Find the average value and rms value.
Given: Peak value, Vm = 12 V
Formulae: Average value, Vavg = 0.637 Vm.
RMS value, Vrms = 0.707 Vm.
Solution: Average value, Vavg = 0.637 Vm
Vavg = 0.637 * 12
Vavg = 7.644 V.
RMS value, Vrms = 0.707 Vm
Vrms = 0.707 * 12
Vrms = 8.484 V
Answer: Vavg = 7.644 V; V rms = 8.484 V
Question 9: Define rms value.
Answer: The rms value or effective value of an alternating current is that value of steady direct current which produces the same heat as that produced by the alternating current when passed through the same resistor for the same interval of time.
Question 10: Define form factor.
Answer: Form factor is the ratio of rms value to the average value of an alternating quantity.
Question 11: Define power factor.
Answer: The power factor is the cosine of the phase angle between voltage and current.
Power factor = cosφ
Question 12: List the types of indicating instruments.
Answer: The types of indicating instruments are,
· Moving coil instruments,
· Moving iron instruments,
· Dynamometer type instruments.
Question 13: Mention the torques required for the proper operation of indicating instrument.
Answer: The operating torques in indicating instruments are,
· Deflecting torque,
· Control torque,
· Damping torque.
Question 13: State the different types of instruments based on their operating principle.
Answer: The different types of instruments are,
· Moving coil instruments,
· Moving iron instruments,
· Induction type instruments,
· Dynamometer type instruments.
Question 14: What are the advantages of electromechanical measuring instruments?
Answer: The advantages of electromechanical measuring instruments are,
· Uniform Scale,
· No hysteresis loss,
· Good accuracy and sensitivity.
Question 15: List the different types of control and damping systems used in instruments.
Answer:
1. The types of Control torque are,
· Spring control,
· Gravity control.
2. The types of Damping torque are,
· Air friction damping,
· Eddy current damping.
Also Read:
GE 6252 - Two Marks Questions & Answers - Unit 5
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