50 Viva Questions and Answers for CBSE Class 12 Physics Practical Exam 2024-25

The CBSE Class 12 Physics Practical Exam is a crucial part of the curriculum, designed to test not only your theoretical knowledge but also your understanding of experimental physics. To help you ace your viva, we have compiled 50 important questions and their answers, categorized by experiments.

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1. General Questions

1. What is the least count of a vernier caliper?
   • The least count of a vernier caliper is typically 0.01 cm or 0.1 mm.
2. Define the least count of a screw gauge.
   • It is the smallest measurement a screw gauge can measure, usually 0.01 mm.
3. What is the principle of a potentiometer?
   • A potentiometer works on the principle that the potential difference across a wire is directly proportional to its length, provided the wire has a uniform cross-sectional area and constant current.
4. Why is a galvanometer not used to measure heavy currents?
   • A galvanometer is sensitive and can only measure small currents. Heavy currents can damage its coil.
5. What is the significance of least count?
   • It determines the accuracy and precision of an instrument.

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2. Experiments Related to Mechanics

6. What is a simple pendulum?
   • It is a mass (bob) attached to a fixed point via a string that swings back and forth under gravity.
7. Why do we neglect air resistance in a pendulum experiment?
   • To simplify calculations and focus on the theoretical principles.
8. Define time period.
   • The time taken by the pendulum to complete one full oscillation.
9. What is the relation between length and time period of a pendulum?
   • T=2πLgT = 2\pi \sqrt{\frac{L}{g}}
10. Why is a small angle of oscillation preferred in a simple pendulum experiment?
    • To ensure that the motion remains simple harmonic.

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3. Optics Experiments

11. What is the focal length of a convex lens?
    • The distance between the optical center and the focal point.
12. How is the refractive index calculated?
    • Refractive Index (n) = sin⁡isin⁡r\frac{\sin i}{\sin r}, where ii is the angle of incidence, and rr is the angle of refraction.
13. Why do we use a sodium lamp in experiments involving a spectrometer?
    • It provides monochromatic light, which is essential for precise measurements.
14. What is the difference between real and virtual images?
    • A real image can be projected on a screen; a virtual image cannot.
15. What is the function of a prism?
    • A prism disperses white light into its constituent colors due to refraction.

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4. Current Electricity Experiments

16. State Ohm’s Law.
    • The current through a conductor is directly proportional to the voltage across it, provided the temperature remains constant.
17. What is the unit of resistance?
    • Ohm (Ω\Omega).
18. Why do we use a low-resistance wire in a potentiometer?
    • To reduce the effect of resistance and maintain a uniform potential gradient.
19. What is the function of a rheostat?
    • A rheostat is used to vary the resistance in a circuit.
20. Why is the ammeter connected in series?
    • To measure the current flowing through the entire circuit.

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5. Semiconductors and Electronics

21. What is a semiconductor?
    • A material whose conductivity lies between that of conductors and insulators.
22. What is the difference between n-type and p-type semiconductors?
    • n-type has an excess of electrons, while p-type has an excess of holes.
23. What is the function of a diode?
    • A diode allows current to flow in one direction only.
24. What is a Zener diode?
    • A special type of diode that conducts in the reverse direction when a certain voltage is reached.
25. Define rectification.
    • The process of converting alternating current (AC) into direct current (DC).

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6. Magnetism Experiments

26. What is the unit of magnetic field strength?
    • Tesla (T).
27. What is the principle of a tangent galvanometer?
    • It works on the principle that a current-carrying coil in a magnetic field experiences torque.
28. What is magnetic susceptibility?
    • It is the measure of how much a material can be magnetized.
29. What are magnetic lines of force?
    • Imaginary lines that represent the direction of the magnetic field.
30. What is the Earth’s magnetic field?
    • The magnetic field surrounding the Earth, caused by the movement of molten iron in its core.

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7. Errors and Measurements

31. What is a systematic error?
    • Errors that occur consistently and can be corrected.
32. Define random error.
    • Errors that occur unpredictably and cannot be corrected easily.
33. What is least count error?
    • The error associated with the resolution of the measuring instrument.
34. How do you calculate percentage error?
    • ( \text{Percentage Error} = \frac{\text{Measured Value – True Value}}{\text{True Value}} \times 100 %
35. What are parallax errors?
    • Errors due to incorrect positioning of the observer’s eye.

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8. Miscellaneous Questions

36. What is resonance?
    • The condition where the natural frequency matches the driving frequency, resulting in maximum amplitude.
37. Define drift velocity.
    • The average velocity of electrons in a conductor due to an applied electric field.
38. What is the principle of conservation of energy?
    • Energy cannot be created or destroyed; it can only be transformed.
39. What is meant by critical angle?
    • The angle of incidence at which the refracted ray grazes the surface.
40. What is total internal reflection?
    • When light reflects entirely back into a medium at an angle greater than the critical angle.

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9. Numerical Problem-Based Questions

41. Calculate the equivalent resistance for resistors in series.
    • Req=R1+R2+R3+…R_{\text{eq}} = R_1 + R_2 + R_3 + \dots
42. Calculate the equivalent resistance for resistors in parallel.
    • 1Req=1R1+1R2+1R3+…\frac{1}{R_{\text{eq}}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + \dots
43. How do you calculate the power dissipated in a resistor?
    • P=I2RP = I^2R
44. What is the formula for kinetic energy?
    • KE=12mv2KE = \frac{1}{2}mv^2
45. Define potential energy.
    • The energy possessed by a body due to its position or configuration.

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10. Advanced Questions

46. What is Heisenberg’s Uncertainty Principle?
    • It states that it is impossible to simultaneously measure the exact position and momentum of a particle.
47. Define wave-particle duality.
    • Light and matter exhibit both wave-like and particle-like properties.
48. What is superconductivity?
    • The property of zero electrical resistance in certain materials below a critical temperature.
49. Explain the photoelectric effect.
    • The emission of electrons from a metal surface when light of sufficient energy strikes it.
50. What is Planck’s constant?
    • A fundamental constant with a value of 6.63×10−34Js6.63 \times 10^{-34} \text{Js}.

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With this comprehensive list of viva questions, you can prepare effectively for your CBSE Class 12 Physics Practical Exam 2024-25. Remember, confidence and clarity in concepts are key to performing well!