SUB: PHYSICS MARKS: 50

CLASS: II PUC TIME: 1.5 Hrs

Dated: 25.6.2013. Pre-quarterly.

**Instructions: **

* Numerical problems solved without writing the relevant formulae carry no marks

** Answers without relevant diagrams/circuits wherever necessary will not carry any marks

**PART-A**

## I. Answer all the following questions (1×5)

1. Where would **Coulomb’s interaction** be weaker in dielectric medium or vacuum?

2. Between **dipole and a point charge** whose Electric Potential** reduces faster?**

3. What is the **work done** when a charge makes a rectangular path **on an equi-potential surface**?

4. Write the **de-Broglie formula for wavelength** of a wave-particle if its momentum is p?

5. Define refractive index from **angle of incidence** and **angle of reflection**.

**PART-B**

## II. Answer any Five of the following questions, 2 marks each. (2×5=10)

6. State how density of **electric lines of force** is related to the **Electric Field Vector intensity E. **Also mention another property of the lines of forces and one property of the equipotential surface.

7. Write the Gauss law of electrostatics and define Electric Flux for a uniform field E.

8. How one defines the direction of a Dipole Vector? What’s the potential vertical to the dipole axis?

9. What’s the energy of an electron if we place it in a potential difference of 100 Volt assuming its at rest at this location? What will be the energy of an alpha-particle if its placed at the same location at rest.

10. Define atomic number and atomic mass unit.

11. Write out the expression of **n-th level** atomic spectra {**energy level**} of a Hydrogen atom. What energy will be released if the electron jumps from **level=5 to level = 3**. ?

12. Write out the mirror equation. If an image is at 10 cm and object at 100 cm what’s the focal length of the mirror?

13. If **angle of incidence is 45 ^{0} **and

**angle of refraction is 30**what will be the refractive index of the medium?

^{0}**PART-C**

## III. Answer any one of the following questions (5×1)

14. Derive the **Electric Field Vector ****E _{||}**

**for the**

**Dipole Vector**

**P**in a

**direction of alignment with the Dipole Vector**, also called

**End-On configuration.**

** **

15.** **Derive the scalar potential V(r) in a general direction **at angle ****J to the Dipole**.

## IV. Answer any two of the following questions (5×2)

16. Define **Electric flux ****F (Phi)** in 1 or 2 lines and write out expression for it for a uniform** and non-uniform electric field E**. State **Gauss Law** in terms of charge and flux in differential and integral form. State the vector form of **Coulomb’s law of electrostatics force**. What’s the flux of a vector if it is aligned to the area vector?

17. Define **Lines of force** and **flux of a vector**. State **Gauss law** and derive its mathematical form by considering **spherical symmetry**.

18. Obtain an expression for the Nuclear Size of an atom by solving for **distance of closest approach (****r)**. Use an incoming alpha-particle of mass m_{α} and charge **q** that’s deflected by the presence of a nucleus of atomic number Z to obtain **r. **Now replace the variables by some numerical: m_{α = }_{6.8×10}^{-27}kg, e = 1.6 x 10^{-19 }coul, Z=100, and v_{α}= 1.0×10^{7} m/s. Express the answer in Femto-meters.

## V. Answer any three of the following questions (5×3)

19. A proton has a radius R and the charge Q is uniformly distributed. Use **Bohr’s atomic energy level formula **for the 1^{st} excited state {**n=2**} and ground state (n=1) to obtain energy of the Hydrogen-atom.

20. State the **power of a lens** and **thin lens formula**. For thin lens case determine the **focal length** if the **object** distance is 100 cm and **image** distance is 25 cm.

** **

21. Draw a simple and neat diagram showing a **convex lens, optical center and focal point** {Focus}. Now define **power of a lens** and obtain an expression for it.

22. Write the expression for the Electrostatics Potential of a point charge. Calculate the potential for a Nitrogen nucleus at a distance of 1 femto-meter (1 fm = 10^{-15 }meters) {Z _{nitrogen}=14}. Also do this for N=10.

## V. Answer the following questions (5×1)

23. Following readings were obtained in one experiment you have performed to determine the focal length of a convex lens by u-v method. Follow the data in the table, u, v, x, y and plot the graph between x and y and obtain the slope S. Then determine the focal length from the slope.

SN | Object O cm | Lens L cm | Image I cm | u (cm) | v (cm) | x=20/u | y=20/v |

1 | 1.0 | 29.0 | 45.5 | ||||

2 | 6.0 | 29.0 | 48.5 | ||||

3 | 11.0 | 29.0 | 59.0 | ||||

4 | 16.0 | 35.0 | 59.0 | ||||

5 | 21.0 | 40.0 | 64.0 |

Determine s = slope, y_{0 }and f = focal length=20/y_{0}.