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Physics lab Viva questions ( Newton's ring experiment, thevinion and Norton's theorem )

Physics lab Viva questions (Newton's ring experiment, thevinion and Norton's theorem)


Viva questions on Newton's ring experiment



1. What are Newton’s Rings?

A.Alternate dark and bright rings formed due to presence of air film when plano convex lens is placed on glass plate is called newtons rings.


2. How are Newton’s rings formed?

A.They are formed as a result of interference between light waves reflected from the upper and lower surfaces of the air film developed between the convex surface of plano convex lens and plane glass plate.

3. Why are they circular?

A.This is so because the air film formed is wedge shaped and loci of points of equal thickness are circles concentric with point of contact.

4. what is the function of the 45° inclined glass plate?

A.It turns the light rays coming from an extended source to ninety degrees and so the rays fall normally on the plano convex lens.

5. Why do rings get closer as their order increases?

A.The diameter of dark rings is proportional to the square root of natural numbers while bright rings are proportional to the square root of odd natural numbers hence the don’t increase at the same rate.

6. Why is the center of the ring dark?

A.At the point of contact the path difference is zero but one of the rays is reflected so the effective path difference becomes  λ/2 thus the condition of minimum intensity is created hence it is a dark spot.

7. What if the glass plate is replaced with plane mirror?

A.Then we will not get interference fringe because the intensity of light reflected from mirror will be so great that it won’t be visible and we will get uniform illumination.

8. What if sodium light is replaced with white light?

A.Few colored fringes will be observed near the center.

9. What will happen if we replace the lens with plane glass?

A.Then interference will take place but the shape of the rings will be irregular.

10. What will happen if few drops of liquid is introduced between the lens and glass?

A.The diameter of the rings will decrease because the diameter of the rings is inversely proportional to the refractive index.

11. What will happen if we use a lens of small radius of curvature?

A.Then the rings will be of smaller diameter and there is chance of error while taking the readings.

12. What if a plane glass making some angle with the glass stripe  is used in place of lens?

A.Then we will have dark and bright fringes in shape of a line. Newtons ring experiment



Important Thevenin’s Theorem Questions with Answers


1) State Thevenin’s Theorem.

Thevenin’s Theorem shows that it is possible to simplify any linear electric circuit to an equivalent electric circuit with one voltage source and series resistance, no matter how complicated the circuit is.

2) What is Thevenin Voltage?

It is the open-circuit voltage that is present over the given two terminals.

3) What is the application of Thevenin’s Theorem?

Circuit analysis of power systems is done using Thevenin’s Theorem.

4) Can Thevenin’s Theorem be applied to a non-linear circuit?

No, applying Thevenin’s Theorem to a non-linear circuit is not possible.

5) Can Thevenin’s Theorem be applied to AC circuits?

Yes, Thevenin’s Theorem can be applied to AC circuits with linear elements like inductors, capacitors, and resistors.

6) What are the theoretical limitations of Thevenin’s Theorem?

Thevenin’s Theorem can only be used in linear circuits analysis. Thevenin’s Theorem is not applicable in electrical circuits with magnetic coupling among the load, and any other circuit component.

7) What are the steps to follow Thevenin’s Theorem?

The main steps are:

  1. Find the voltage of the Thevenin source by detaching the load resistor from the given circuit, and measuring the voltage over the open connection junctions where the load resistor is connected.
  2. Calculate the Thevenin resistance by detaching all the power sources in the original electrical circuit (current sources open and voltage sources shorted), and measuring the total resistance across the open connection points.
  3. Draw the derived Thevenin circuit, with the Thevenin resistance in series with the Thevenin voltage source.
  4. Analyse current and voltage for the load resistor following the laws of series electrical circuits.

8) Who derived Thevenin’s Theorem?

Thevenin’s Theorem was independently developed in 1853 by Hermann von Helmholtz and in 1884 by Léon Charles Thévenin.

9) Is it possible to simplify any complex linear circuits?

Yes, by using Thevenin’s Theorem, it is possible to simplify any linear electric circuit, no matter how complicated the circuit is, to an equivalent electric circuit with one voltage source and series resistance.

10) Give a few examples of network analysis theorems.

Thevenin’s Theorem, Superposition Theorem, Maximum Power Transfer Theorem, Norton’s Theorem, etc., are a few examples of network analysis theorems.

11) Thevenin’s Theorem and ____________ are extensively used to make electrical circuit analysis simpler. They are also used to study the initial-condition of a circuit and steady-state response.

Answer: Norton’s Theorem

Explanation: Thevenin’s Theorem and Norton’s Theorem are extensively used to make electrical circuit analysis simpler. They are also used to study the initial-condition of a circuit and steady-state response.

12) What is a steady-state response?

A steady-state response is the nature of an electrical circuit after an extended time when steady states have been attained after an external excitation.

13) Compare Thevenin’s Theorem and Norton’s Theorem.

  • Thevenin’s Theorem utilises a voltage source, while Norton’s Theorem uses a current source.
  • Norton’s Theorem employs a resistor set in parallel over the source, whereas Thevenin’s Theorem utilises a resistor in series.
  • From Thevenin’s Theorem, Norton’s Theorem can be easily derived.
  • Thevenin’s resistance and Norton’s resistance are equal in value.
  • Thevenin’s equivalent circuit and Norton’s equivalent circuit can be straightforwardly interchanged.

14) What are the practical limitations of Thevenin’s Theorem?

The practical limitations of Thevenin’s Theorem:

  • Many electrical circuits are only linear within a certain range of values. Therefore, Thevenin’s Theorem is only valid along this linear range.
  • The Thevenin’s equivalent has equivalent I-V characteristics only from the load’s point of view.
  • The Thevenin equivalent’s power dissipation is not strictly identical to the real system’s power dissipation. But power dissipated by an external resistor among two output terminals is identical, despite how the internal resistance is.



Important Norton's Theorem Questions with Answers


Question No. 01: What is Q factor?
Answer: The Q factor is ratio of inductive reactance to resistance of a coil.

Question No. 02: List examples of current sources?
Answer: Semiconductor devices like transistor and diode are treated as current sources.

Question No. 03: State Norton’s theorem?
Answer: This theorem states that any linear bilateral network with active network with output terminals AB can be replaced by a single current source in parallel with a single impedance Z.

Question No. 04: What is the efficiency during maximum power transfer?
Answer: Efficiency during maximum power transfer 50%.

Question No. 05: Define filter?
Answer: A filter is an electrical network that can transmit signals within a specified frequency range.

Question No. 06: Define active filter?
Answer: The active filter contains components like operational amplifier that introduce some gain in the signal.

Question No. 07: How a band pass filter is constructed?
Answer: This filter is a combination of two parallel tuned circuits. This is a special type of LC filter along with a particular BW frequency to be allowed through it.

Question No. 08: What is resistance?
Answer: The resistance is the property of a material to oppose the flow of current in a material. Its unit is ohm.

Question No. 09: What happens to voltage when current is zero?
Answer: The voltage is constant.

Question No. 10: Which capacitor is preferred for high voltage and frequency?
Answer: The vacuum and gas filled capacitor are used for high voltage and frequency applications.

Question No. 11: State Kirchoff’s voltage law?
Answer: Kirchoff’s voltage law states that the algebraic sum of all branch voltages around any closed loop of a network is zero at all instant of time.

Question No. 12: What is the limitation of Kirchoff’s law?
Answer: It fails in distributed parameter network.

Question No. 13: Sate Maximum power transfer theorem?
Answer: A resistance load being connected to a dc network receives maximum power when load resistance is equal to internal resistance.

Question No. 14: Define characteristics impedance?
Answer: The characteristics impedance of a filter matches with circuit to which it is connected throughout the pass band.

Question No. 15: List the disadvantages of constant K filters?
Answer: The attenuation does not increase rapidly beyond cut-off frequency. Characteristics impedance varies widely in the pass band from desired value.

Question No. 16: What are the materials used for resistor?
Answer: The materials used are:
  1. Manganin (alloy of copper, manganese and nickel. Copper86%, Manganese 12%, and Nickel 2%)
  2. Constantan (alloy of nickel and copper. Copper 55% and Nickel 45%).

Question No. 17: When we use 3-terminal resistor?
Answer: It is used when resistance is less than 1 ohm.

Question No. 18: State Kirchoff’s current law?
Answer: The algebraic sum of currents at any node of a circuit is zero. The sum of incoming current is equal to sum of outgoing current.

Question No. 19: How equivalent impedance is calculated in Thevenin Theorem?
Answer: All independent voltage sources are short circuited and all independent current sources are open circuited.

Question No. 20: State Superposition theorem
Answer: If a number of voltages or current sources are acting simultaneously in a linear network the resultant current in any branch is the algebraic sum of current that would be produced in it when each source acts alone replacing all other independent sources by their internal resistances.

Question No. 21: Define unilateral circuit?
Answer: The circuit whose properties are not same in either direction is known as unilateral circuit.

Question No. 22: What are the applications of filter?
Answer: The Filter is used in voice frequency telegraphy, multi channel communication, TV broadcasting and telephony.

Question No. 23: What is inductance?
Answer: It is the property of a material by virtue of which it opposes any change of magnitude and direction of current passing through the conductor.

Question No. 24: What are the properties of a resistor?
Answer: The properties are high resistivity, resistance to oxidation, corrosion and moisture.

Question No. 25: State Thevenin Theorem?
Answer: This theorem states that any linear network with output terminal AB can be replaced by a single voltage source V in series with a single impedance.

Question No. 26: Define active and passive network?
Answer:
Active network: The network which has no current or voltage source is called passive network.
Passive network: The network which either has current or voltage source is called active network.

Question No. 27: List the characteristics of filter?
Answer: An ideal filter would transmit signals under the pass-band frequencies without attenuation and completely suppress the signal with attenuation band of frequencies with a sharp cut-off profile.

Question No. 28: Define cut-off frequency?
Answer: The frequency that separates the pass and attenuation band is known as cut-off frequency.

Question No. 29: What happens to voltage when current through the inductor is constant?
Answer: The voltage across inductor is zero.

Question No. 30: What is the material used for inductance coil?
Answer: The material used is marble because it is unaffected by atmospheric conditions.

Question No. 31: Is the theorem applicable to a.c. sources?
Answer: No, it is applicable to dc circuits with and without controlled sources.

Question No. 32: State Ohm’s Law?
Answer: The current through any conductor is directly proportional to the applied potential difference across it keeping physical condition unchanged.

Question No. 33: What are dependent sources?
Answer: When strength of voltage or current changes in the source for any change in the connected network they are called dependent sources.

Question No. 34: How will you define capacitance?
Answer: It is the ability to store electric charge within it. Capacitance is a measure of charge per unit voltage that can be stored in an element.

Question No. 35: Define Norton equivalent circuit?
Answer: The Norton equivalent circuit is a current generator which is placed in parallel to internal resistance.

Question No. 36: What is the unit of charge and current?
Answer: The units are coulomb and ampere.

Question No. 37: List examples of voltage source?
Answer: The examples of voltage source are battery and generator.

Question No. 38: Define branch?
Answer: It is a part of a network which lies between two junction points.

Question No. 39: What is the unit of attenuation?
Answer: The unit is decibel and neper.

Question No. 40: List advantages of active filter over passive filter?
Answer: Active filter eliminate bulky components. It offers gain. It can drive low impedance loads. It is easy to tune.

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