CBSE Class 12 Physics Viva Questions with Answers 2025: Top Physics Practical Viva Solutions PDF Download

Physics Viva Questions Class 12: The Central Board of Secondary Education (CBSE) practical exams are about to start, and it's time for Class 12 students to start revising the viva questions. The examiner won’t expect very lengthy replies but very crisp and concise answers. Thus, prepare accordingly and do not involve yourself in explaining the whole concept. Go through the questions provided here for Class 12 Physics Viva 2025.

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CBSE Class 12 Physics Practical Exam Date 2025

As per cbse.gov.in, the Class 12th practical exams will be conducted from January 1, 2025. The exact date for the Physics practical cannot be conveyed as it varies from school to school and the availability of the examiner. The expected date for the CBSE Class 12 Physics practical will fall in the first and second week of January. The administration will not delay this process further due to the 2nd pre-board and the CBSE board examinations.

Check | CBSE Class 12 Pre-Board Question Papers (All Subjects)

CBSE Class 12 Physics Top Viva Questions With Answers

Below are the 100+ Physics viva questions for Class 12 students. They can quickly go through them and revise what they have learnt throughout the year. It won’t take much time but might help you get a 30/30 score in the practical exam.

1. Define Ohm’s law.
   Answer: Ohm’s law states that the current flowing through a conductor is directly proportional to the voltage across it, as long as the temperature and other physical conditions remain constant.
2. What is the formula of Ohm’s law?
   Answer: The formula for Ohm’s law is: V=IRV

Here, V is voltage, I is current, and R is resistance.

3. What is the unit of resistance?
   Answer: The unit of electrical resistance is the Ohm (Ω).
4. What is the SI unit of potential difference?
   Answer: The SI unit of potential difference is volt (V).
5. What is the unit of current?
   Answer: The unit of electric current is ampere (A).
6. Does resistance depend on temperature?
   Answer: Yes, resistance increases as the temperature of the conductor rises.
7. Does resistance depend on the dimensions of the conductor?
   Answer: Yes, resistance depends on the length and cross-sectional area of the conductor.
8. What is specific resistance?
   Answer: Specific resistance, or resistivity, is the resistance offered by a material per unit length and unit cross-sectional area under an applied voltage.
9. What is the SI unit of resistivity?
   Answer: The SI unit of resistivity is ohm-metre (Ω·m).
10. What is electrical conductivity?
    Answer: Electrical conductivity measures how easily a material allows an electric current to pass through it.

Check | CBSE Class 12 Deleted Syllabus 2025

11. Define a rheostat.
    Answer: A rheostat is a variable resistor with two terminals. It is used to adjust the current flowing through a circuit.
12. What material is used in a rheostat’s wire?
    Answer: The wire in a rheostat is usually made of constantan or manganin.
13. What is a metre bridge?
    Answer: A metre bridge, or slide wire bridge, is a device based on the Wheatstone bridge principle. It is used to measure the unknown resistance of a conductor.
14. How does temperature affect resistance?
    Answer: As the temperature increases, the resistance of a conductor also increases.
15. What is superconductivity?
    Answer: Superconductivity is a state where certain materials exhibit zero resistance when cooled below a specific temperature.
16. How is a galvanometer converted into (a) a voltmeter and (b) an ammeter?
    Answer:
    (a) To convert a galvanometer into a voltmeter, a high resistance is connected in series with it.
    (b) To convert it into an ammeter, a low resistance is connected in parallel with it.
17. What is the difference between potential difference and emf?
    Answer:

• Potential difference is the work done to move a unit charge between two points in a circuit.
• Emf is the potential difference across the terminals of a cell when no current is flowing.

18. Why are connecting wires thick and covered with cotton?
    Answer: Thick wires have very low resistance, and the cotton covering prevents short-circuiting.
19. In a series combination of resistors, how is the total resistance calculated?
    Answer: In a series combination, the total resistance RT is the sum of the individual resistances:

RT=R1+R2+R3+…+Rn

20. What happens if a voltmeter is connected in series?
    Answer: A voltmeter, which measures potential difference, has high resistance. Connecting it in series greatly reduces the current in the circuit, which can affect its operation.
21. Is Ohm’s law universal?
    Answer: No, Ohm’s law is not universal. It does not apply to semiconductors or materials at extremely low temperatures.
22. What is a Wheatstone bridge?
    A Wheatstone bridge is a type of electrical circuit used to measure an unknown resistance by balancing two legs of the bridge circuit. One leg contains the unknown resistor.
23. What is the balanced condition of a Wheatstone bridge?
    The Wheatstone bridge is balanced when no current flows through the galvanometer. This happens when the known and variable resistances are adjusted correctly.
24. What principle does the metre bridge follow?
    The metre bridge works on the principle of the Wheatstone bridge.
25. What is the use of a metre bridge?
    A metre bridge is used to measure the resistance of a resistor precisely.
26. What material is used to make the wire in a metre bridge?
    Materials like nichrome, constantan, or manganin are used because they have high resistance and a low temperature coefficient, meaning their resistance doesn’t change much with temperature.
27. When is the metre bridge most sensitive?
    The metre bridge is most sensitive when all four resistors in the circuit have equal resistance.
28. What are the limitations of a Wheatstone bridge?
    A Wheatstone bridge becomes less accurate when measuring very low resistances because the resistance of leads and contacts affects the results.
29. What is Ohmic resistance?
    Ohmic resistance is resistance that follows Ohm's law.
30. What are some examples of Ohmic resistance?
    Examples of Ohmic resistance include silver, aluminium, and copper.
31. What is non-ohmic resistance?
    Non-ohmic resistance is resistance that does not follow Ohm's law.
32. What are some examples of non-ohmic resistance?
    Vacuum tube diodes and transistors are examples of non-ohmic resistance.
33. Is a semiconductor diode an ohmic or non-ohmic resistance?
    A semiconductor diode is a non-ohmic resistance.
34. What is meant by the e.m.f of a cell?
    The e.m.f of a cell is the maximum potential difference between its terminals when no current is flowing through the circuit.
35. What is terminal voltage?
    Terminal voltage is the potential difference across a cell’s terminals when it is supplying current.
36. What is a potentiometer?
    A potentiometer is a device used to measure small potential differences accurately and compare the e.m.f of different cells.
37. What is the principle of a potentiometer?
    The principle of a potentiometer states that the potential drop along a uniform wire carrying a steady current is directly proportional to the length of the wire.
38. What is meant by a potential gradient?
    A potential gradient is the change in potential per unit length of the potentiometer wire.
39. Why is a potentiometer preferred over a voltmeter for measuring e.m.f?
    A potentiometer is better for measuring e.m.f because it takes no current from the cell during measurement, ensuring an accurate reading.
40. How is an ammeter connected in a circuit?
    An ammeter is always connected in series in the circuit.
41. How is a voltmeter connected in a circuit?
    A voltmeter is always connected in parallel with the component being measured.
42. How is a galvanometer converted into an ammeter?
    A galvanometer is turned into an ammeter by connecting a low resistance wire (shunt) in parallel with it.
43. How is a galvanometer converted into a voltmeter?
    A galvanometer is converted into a voltmeter by connecting a high resistance in series with it.
44. Give an example of a substance whose resistance decreases as temperature increases.
    A semiconductor is a good example, as its resistance reduces when the temperature rises.
45. Is a voltmeter used for measuring the e.m.f.?
    

No, the voltmeter takes electric current from the cell.

46. What is the reason behind the null point?

The null point is acquired because the cell’s e.m.f. is balanced by the potential variation along a particular length of the connected potentiometer wire.

47. What is meant by a cell’s internal resistance?

The resistance applied by the cell’s electrolyte is known as the cell’s internal resistance.

48. What is meant by a primary cell?

A primary cell is a type of cell which cannot be recharged.

49. What is meant by a secondary cell?

A secondary cell is a type of cell which can be recharged.

50. Why does a secondary cell give more electric current than a primary cell of the identical e.m.f.?

A secondary cell gives more electric current than a primary cell because a secondary cell possesses a very low internal resistance.

51. Which type of cells (primary cells or secondary cells) is employed in automobiles?

Secondary cells are typically used in automobiles because they provide the needed large beginning current due to this cell’s relatively low internal resistance.

52. Is sensitivity impacted by potential gradients?

Yes, the lesser the potential gradients, the higher will be the sensitivity.

53. How is the potentiometer’s sensitivity affected by the length of the wire?

The sensitivity of the potentiometer rises with the increase in the wire’s length.

54. On what constraints does the cell’s internal resistance depend?

In the case of a cell, internal resistance depends on:

• nature of the electrolyte
• the concentration of the electrolyte nature of the electrodes
• distance between the plates temperature
• area of the plates inside the electrolyte

55. Can a potentiometer be used to calculate the secondary cell’s internal resistance?

No, a secondary cell possesses very little internal resistance. Due to the low value, it has no considerable effect on the potential difference.

Check:

• CBSE Class 12 Syllabus 2024-25 PDF

• CBSE Class 12 Sample Paper With Answer Key 2024-25

56. What can be the reason for one-sided deflection in galvanometers?

1. The primary cell’s e.m.f. may surpass that of the main circuit cell.
2. Circuit connections may be incorrect or loose.

57. What is electrical resistance?

Electrical resistance is the hindrance provided by a material in the flow of current; it is the physical property of a substance which allows it to oppose the flow of electrons, that is, current. Resistance is inversely proportional to the cross-sectional area of the material and directly proportional to the temperature and length of the material.

58. What is direct current?

Direct current is the current whose direction remains the same. From a region of high electron density to a region of low electron density, the flow of electrons in a direct current is constant. Direct current is widely used in applications that involve a battery and many household appliances.

59. Why is Ohm’s law not applicable to semiconductors?

The semiconductors are nonlinear devices, and this is the reason why Ohm’s law is not applicable to semiconductors. This means that for variations in voltage, the ratio of voltage to current doesn’t remain constant.

60. When does Ohm’s law fail?

When semiconductors and unilateral devices such as diodes come into play, Ohm’s law fails to give the desired result because, in these materials, the physical conditions, such as temperature or pressure, do not remain constant.

61. What is the unit to measure electric current?
    Answer: Ampere is the unit used to measure the electric current.
62. Define ampere.
    Answer: An ampere is a unit of measure of the rate of electron flow or current in an electrical conductor.
63. On the galvanometer scale, why is zero placed in the middle?
    Answer: Zero is placed in the middle of the galvanometer since the galvanometer needle can deflect on both sides.
64. Are there positive and negative terminals in the galvanometer?
    Answer: There are no positive and negative terminals in the galvanometer.
65. A galvanometer is known as the fundamental electrical measuring tool. Why?
    Answer: A galvanometer is known as the fundamental electrical measuring tool because it is designed to measure voltage and current.
66. Should the galvanometers possess a high or low resistance?
    Answer: Galvanometers should possess a low resistance.
67. What is the main procedure to convert a galvanometer into a voltmeter?
    Answer: A galvanometer is usually changed into a voltmeter by joining a large resistance in series with it.
68. Should voltmeters possess low resistance or high resistance? Why?
    Answer: Voltmeters should always possess a large resistance; if not, it will decrease the potential difference it is intended to measure.
69. What is the resistance value of ideal voltmeters?
    Answer: Ideal voltmeters have infinite resistance.
70. Should ammeters have high or low resistance? Why?
    Answer: Ammeters should always possess a low resistance; otherwise, they will decrease the current it is intended to calculate.
71. A galvanometer is transformed into a milliammeter and an ammeter. Which of the two devices will have better resistance?
    Answer: The milliammeter will possess better resistance.
72. What is the resistance value of ideal ammeters?
    Answer: Ideal ammeters have zero resistance.
73. What do you mean by a galvanometer’s figure of merit?
    Answer: A galvanometer’s figure of merit is the electric current needed to generate a one-division deflection in the galvanometer.
74. What is shunt resistance?
    Answer: Shunt resistance is a low-value resistance connected in parallel with an ammeter to extend its range or measure the load current when connected in series.
75. What is the reduction factor?
    Answer: The reduction factor is the current required to produce a 45° deflection in a tangent galvanometer. It is measured in amperes and denoted by K.
76. Why is an ammeter always connected in series?
    Answer: Since the internal resistance of an ammeter is low, it is always connected in series. There is a high risk of short-circuiting if connected in parallel.
77. How does current electricity differ from static electricity?
    Answer: Current electricity involves the continuous flow of charges, while static electricity is the result of separated charges that remain stationary until discharged.
78. What is static electricity?
    Answer: Static electricity occurs when positive and negative charges are separated, creating a build-up of charge on a surface. It is often caused by friction.
79. What is a voltmeter?
    Answer: A voltmeter is a device used to measure the potential difference or voltage between two points in an electrical circuit.
80. What is the working principle of a voltmeter?
    Answer: A voltmeter works on the principle that it must be connected in parallel with the circuit. Its high resistance ensures that the measured voltage is not affected.
81. What is a sonometer?
    Answer: A sonometer is a device used to study the relationship between the frequency of sound produced by a plucked string and its length, tension, and mass per unit length.
82. What is alternating current (AC)?
    Answer: Alternating current is a type of electrical current that changes its magnitude and polarity at regular intervals.
83. What is direct current (DC)?
    Answer: Direct current flows in a single direction with a constant magnitude. For example, a mobile battery supplies DC.
84. List two uses of a sonometer.
    Answer: A sonometer is used to determine the frequency of a tuning fork and measure the tension in a string.
85. Can the frequency of alternating current be found using the sonometer?
    Answer: Yes, the frequency of alternating current can be determined using a sonometer.
86. What is the unit of frequency of alternating current?
    Answer: The unit of frequency of alternating current is hertz (Hz).
87. Define an electromagnet.
    Answer: An electromagnet is a magnet that can be magnetised using an electric current.
88. What is the formula to calculate the percentage of error?
    Answer: The percentage of error is given by the formula: Percentage error=(DifferenceActual Value)×100%

89. How is direct current different from alternating current?
    Answer: Direct current has a constant magnitude and flows in one direction, while alternating current varies in magnitude and direction periodically.
90. What is the spherical mirror used in this experiment?
    Answer: A concave mirror is used in this experiment.

Check | CBSE Topper Answer Sheet Class 12

91. What are the two types of spherical mirrors?
    Answer: The two types of spherical mirrors are convex mirrors and concave mirrors.
92. Which type of mirror always generates a virtual image?
    Answer: Convex and plane mirrors always generate virtual images.
93. What is the aperture of a spherical mirror?
    Answer: The aperture is the diameter of the circular rim of the spherical mirror.
94. Define the pole of a concave mirror.
    Answer: The pole is the centre of the reflecting surface of the concave mirror, denoted by PPP.
95. Define the centre of curvature on a concave mirror.
    Answer: The centre of curvature is the centre of the sphere of which the concave mirror is a part, denoted by C.
96. Define the centre of curvature on a spherical mirror.
    Answer: The centre of the sphere from which the spherical mirror is made is called the centre of curvature.
97. What is the correlation between the radius of curvature (R) and focal length (F) of a concave mirror?
    Answer: The relationship is given by F=R/2.
98. Define the principal axis of a spherical mirror.
    Answer: The principal axis is the imaginary line that passes through the pole and the centre of curvature of the spherical mirror.
99. What is the radius of curvature of a concave mirror?
    Answer: The radius of curvature is the radius of the sphere from which the concave mirror is derived.
100. Define the principal focus on a concave mirror.
     Answer: The principal focus is the point on the principal axis where parallel rays converge after reflecting from a concave mirror.
101. What are the two types of lenses generally used?
     Answer: The two types of lenses are concave lenses and convex lenses.
102. Is the convex lens’s focal length taken as negative or positive?
     Answer: The convex lens’s focal length is taken as positive because it converges light rays.
103. Why doesn’t a plane mirror generate a real focus like a convex mirror?
     Answer: In a plane mirror, reflected rays do not converge; instead, they appear to diverge from a point, creating a virtual image.

104. What is the mirror formula?

Answer: The mirror formula is given by, 1/f = 1/v+1/u

-f is the focal length

-u is the object distance v is the image distance

105. Define the law of reflection for mirrors?

Answer: The incident ray, the reflected ray and the normal all exist in the exact same plane.

∠i = ∠r

106. Give the number of refracting surfaces a lens possesses.

A lens has two refracting surfaces.

107. What is the ideal position of a body if you want to get an image of the same dimension in the case of a concave mirror?

Answer: The body should be positioned at ‘C’ of a concave mirror in order to get an image of the same dimension.

108. Which is the mirror typically used for shaving? Why?

Answer: The concave mirror is typically used for shaving. This is mainly due to the fact the object is positioned between the focus and pole of the mirror. The resulting image will be virtual and magnified.

109. Consider a situation where you are standing in front of a mirror, and the image looks as follows:

Answer: The head looks to be very large, the body looks to be normal size, and the legs look to be tiny.

110. What is the nature of mirrors used in this scenario?

Answer:  In this case, the mirror is a combination of types of mirrors. The top section is a concave mirror, the middle section is a plane mirror, and the bottommost section is a convex mirror.

111. What are the two main types of mirrors?

Answer: Plane mirrors and spherical mirrors are the two main types of mirrors.

112. What is denoted by the symbol ‘R’ in a concave mirror?

Answer:  The radius of curvature is denoted by the symbol ‘R’ in a concave mirror.

113. Give two general uses of concave

Answer:  Concave mirrors are extensively used by dentists and in solar cookers.

114. What type of images do concave mirrors generate?

Answer:  Concave mirrors generate real and virtual images.

115. If a body is at infinity, where will the image be generated in the case of a concave mirror?

Answer:  The image will be generated at the focus point of the concave mirror if a body is at infinity.

116. When do concave mirrors produce virtual images?

Answer: Concave mirrors produce virtual when objects are positioned between the focal point and pole.

117. What happens when parallel rays strike a convex lens?

Parallel rays converge at the focus of the convex lens.

118. When light rays pass through the optical centre of convex lenses, what happens to the light rays?

Answer:  Light rays will pass through without deviating when it passes through the optical centre of convex lenses.

119. Do the characteristics of the images produced by convex lenses rely on the location of the object?

Answer:  Yes, convex lenses form virtual images only when positioned between the optical centre and the focus point. In the case of all other locations, convex lenses produce real images.

120. How will you distinguish a concave lens from a convex lens experimentally?

Answer: If the given spherical lens produces a real sharp image of a faraway object, it is a convex lens. If not, it should be a concave lens.

121. If half of the concave lens is covered when focusing on a faraway subject, what will be the effect on the image produced?

Answer:  An image will be generated as normal, but the image intensity will be half the original.

122. What is a convex mirror?

Answer: A convex mirror is defined as a spherical mirror that features an outwardly bulged reflecting surface.

123. What is a convex lens?

Answer: A convex lens is a type of lens that is thicker at the centre and thinner at the edges. It converges on a straight beam of light.

124. Explain the type of image formed by the convex mirror.

Answer: A convex mirror always creates only virtual images that are erect and diminished for all object positions.

125. What kind of image is created by the convex lens?

Answer: The convex lenses form real as well as inverted images of different sizes. Erect, virtual, and enlarged images are formed based on the object’s position.

126. What is a convex lens referred to as?

Answer: A convex lens is also referred to as a converging lens.

127. Which type of lens has a negative focal length?

Answer: The concave lens is the lens which has a negative focal length.

128. Define the power of the lens.

Answer: The power of a lens is defined as the reciprocal of the focal length.

129. How is the lens power measured?

Answer: Lens power is measured in dioptres (D).

130. A convex lens is used to treat which type of refractive error in the human eye?

Answer: The convex lens is used to treat hypermetropia or long-sightedness.

131. Why is a convex lens used in cameras?

Answer: A convex lens is used in cameras because it focuses light in order to create a clear and sharp image.

132. What are the types of mirrors?

Answer: Types of mirrors are, Plane mirrors and Spherical mirrors

133. Define focal

Answer: Focal length is the distance between the optical centre and the principal focus of the lens.

134. Is a convex mirror a transparent or opaque object?

Answer: A convex mirror is an opaque object.

135. What happens to the incident ray, which is an incident on a convex lens?

Answer: A convex lens converges the incident rays towards the principal axis.

134. Which lens is known as a diverging lens?

Answer: A concave lens is known as a diverging lens.

135. When a concave lens is combined with a convex lens, what would be the quality of the image?

Answer: A sharper image is formed when a concave lens is combined with a convex lens.

136. The lens works on which principle?

Answer: The lens works on the principles of refraction.

137. Which type of lens is used in the human eye?

Answer: Convex lenses are the lenses used in the human eye.

138. What is an optical aberration?

Answer:  The property of the lens that causes blurriness or distortion during the formation of an image is known as an optical aberration. The light is spread out or dispersed due to optical aberration rather than being focused on a certain fixed point. Optical aberration is an unwanted property of the lens, and by using a grouping of lenses rather than using a single piece of the lens, it can be eliminated.

139. What is magnification?

Answer: Magnification of the lens is basically the ratio of the linear size of the image to the linear size of the object.

m = (linear size of the image/linear size of the object)

140. What is chromatic aberration?

Answer:  Dispersion is the reason why chromatic aberration occurs. Due to chromatic aberration, a lens fails to focus all colours on the same point, and colourful fringes around an image can be observed due to chromatic aberration. An achromatic doublet can be used to fix chromatic aberration.

141. What is total internal reflection?

Answer:  When the light rays travel from a more optically denser medium to a less optically denser medium, the phenomenon that happens is known as total internal reflection.

142. What are optics, and what are their types?

Answer:  The study of the wave properties of light is known as optics, and it is divided into three categories:

Diffraction Interference Polarisation

143. What is wave optics in physics?

Answer: The branch of optics that studies the phenomena for which the ray calculation of geometric optics is not valid, like interference, diffraction, polarisation, and others, is known as wave optics.

144. Does the refractive index affect the power of the lens?

Answer: Yes, the refractive index is one of the factors that affect the power of the lens.

145. When a convex lens is combined with a concave lens, what would be the quality of the image?

Answer: A sharper image is formed when a convex lens is combined with a concave lens.

146. Which lens is used in the magnifier?

Answer: The convex lens is used in the magnifiers.

147. What is a prism?

Answer:  A prism is a transparent optical device with polished, flat surfaces that refract light. At least one of its surfaces must be angled. A similar optical device with two parallel sides is not a prism.

148. How many edges are there in a prism?

Answer: There are nine edges in a prism.

149. What is meant by the angle of deviation?

Answer:  The angle of deviation is the angle at which a light ray turns away from the original way while moving through a prism.

150. What is the angle of minimum deviation?

Answer: The minimum value of the deviation angle is called the angle of minimum deviation.

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