The Central Board of Secondary Education (CBSE) is conducting Class 10 and 12 board exams for the academic year 2025. The exams for the two classes began on February 15, 2025. The CBSE Class 10 exams 2025 started with English as the first subject, while the Class 12 exams began with Entrepreneurship. The exam for Class 12 Physics will be held on February 21, 2025.
Students can visit the official website of the CBSE to check sample papers. Following are some of the important questions from the sample papers.
A compound microscope consists of an objective lens of focal length 2.0 cm and an eyepiece of focal length 6.25 cm separated by a distance of 15 cm. How far from the objective should an object be placed in order to obtain the final image at
a) the least distance of distinct vision (25 cm) and
b) infinity? What is the magnifying power of the microscope in each case?
A giant refracting telescope at an observatory has an objective lens of focal length 15 m. If an eyepiece of focal length 1.0 cm is used, what is angular magnification of the telescope in normal adjustment?
b) If this telescope is used to view the moon, what is the diameter of the image of the moon formed by the objective lens? The diameter of the moon is 3.48 × 106 m, and the radius of lunar orbit is 3.8 × 108 m.
Explain briefly, with the help of a labelled diagram, the basic principle of the working of an a.c.generator. In an a.c. generator, coil of N turns and area A is rotated at an angular velocity ω in a uniform magnetic field B. Derive an expression for the instantaneous value of the emf induced in coil. What is the source of energy generation in this device?
With the help of a diagram, explain the principle of a device which changes a low ac voltage into a high voltage . Deduce the expression for the ratio of secondary voltage to the primary voltage in terms of the ratio of the number of turns of primary and secondary winding. For an ideal transformer, obtain the ratio of primary and secondary currents in terms of the ratio of the voltages in the secondary and primary coils.
b) Write any two sources of the energy losses which occur in actual transformers.
c) A step-up transformer converts a low input voltage into a high output voltage. Does it violate law of conservation of energy? Explain.
Write two limitations of ohm's law. Plot their I-V characteristics.
A heating element connected across a battery of 100 V having an internal resistance of 1 Ω draws an initial current of 10 A at room temperature 20.0 °C which settles after a few seconds to a steady value. What is the power consumed by battery itself after the steady temperature of 320.0 °C is attained? Temperature coefficient of resistance averaged over the temperature range involved is
3.70 × 10–4 °C–1
