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.
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:
- 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.
- 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.
- Draw the derived Thevenin circuit, with the Thevenin resistance in series with the Thevenin voltage source.
- 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
- Manganin (alloy of copper, manganese and nickel. Copper86%, Manganese 12%, and Nickel 2%)
- Constantan (alloy of nickel and copper. Copper 55% and Nickel 45%).
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