CBSE Class 12 Physics Sample Paper 2018 Set D

SET–I

1. Using the concept of force between two infinitely long parallel current carrying conductors, define one ampere of current.

2. To which part of the electromagnetic spectrum does a wave of frequency 5 × 1019 Hz belong?

3. Two equal balls having equal positive charge ‘q’ coulombs are suspended by two insulating strings of equal length. What would be the effect on the force when a plastic sheet is inserted between the two?

4. Define intensity of radiation on the basis of photon picture of light. Write its SI unit.

5. The electric current flowing in a wire in the direction from B to A is decreasing. Find out the direction of the induced current in the metallic loop kept above the wire as shown.

6. Why is it found experimentally difficult to detect neutrinos in nuclear b-decay?

7. Why is the use of AC voltage preferred over DC voltage? Give two reasons.

8. A biconvex lens made of a transparent material of refractive index 1.25 is immersed in water of refractive index 1.33. Will the lens behave as a converging lens? Give reason. 

9. Using Rutherford model of the atom, derive the expression for the total energy of the electron in hydrogen atom. What is the significance of total negative energy possessed by the electron?

OR

Using Bohr’s postulates of the atomic model, derive the expression for radius of nth electron orbit. Hence obtain the expression for Bohr’s radius.

10. A parallel plate capacitor of capacitance C is charged to a potential V. It is then connected to another uncharged capacitor having the same capacitance. Find out the ratio of the energy stored in the combined system to that stored initially in the single capacitor.

11. Considering the case of a parallel plate capacitor being charged, show how one is required to generalise Ampere’s circuital law to include the term due to displacement current.

12. A cell of emf ‘E’ and internal resistance ‘r’ is connected across a variable resistor ‘R’. Plot a graph showing variation of terminal voltage ‘V’ of the cell versus the current ‘I’.Using the plot, show how the emf of the cell and its internal resistance can be determined.

13. Explain, with the help of a circuit diagram, the working of a p-n junction diode as a half-wave rectifier.

14. Estimate the average drift speed of conduction electrons in a copper wire of crosssectional area 1.0 ×10^–7 m² carrying a current of 1.5 A. Assume the density of conduction electrons to be 9 x 1028 m–3.

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