SUB: PHYSICS                                                                           MARKS: 50

CLASS: II ISC                                                                              TIME: 1.5 Hrs

PART-A

Total 8 marks (Compulsory, objective and short-answer questions)

## Each carries 1 mark.  Answer all.                                             (8)

Question 1 [Objective, 3X1]

(a) In an electric dipole, how is the direction of the dipole vector defined?

A. negative charge to positive charge                      B. positive charge to negative charge

C. Perpendicular bisector to axis between positive and negative charge     D. Arbitrary

(b) What’s the Electric Potential of a Dipole Vector in the vertical direction to it?

A. infinite                                      B. zero

C. depends on electric field       D. depends on charge of dipole

(c) Pick only the correct one “Between an alpha-particle and a proton”

A. the alpha particle has more electrostatics potential energy in an electrostatics potential of 100 volt.

B. the proton has more electrostatics potential energy in an electrostatics potential of 100 volt.

C. The alpha particle has more potential energy in a potential of 100 Volt if its traveling faster than proton.

D. The alpha particle has more potential energy in a potential of 100 Volt if its traveling slower than proton.

(d) Give example of 3 conservative forces and state if this is true or not-true: “The work done in a conservative force field during a circular voyage is proportional to the amount of charge on the voyage”?

(e) Define atomic number, atomic mass and neutron number. What’s the atomic number and atomic mass of Helium?

(f) Write out the complete expression of n-th level atomic spectra {energy level} of a Hydrogen atom. What energy will be released if the electron jumps from level=4 to level = 3.  ?

(g) Cigarette smoking causes cancer as cigarette contains radioactive elements during their preparation. The radioactive elements always obey a relation of decay which determines their half-life period if an initial sample is given with a specified number of radioactive elements. Write out the simple expression {formula} for radioactive decay in terms of half-life?

(h) The half-life of (38Chlorine) is 0.62 hours and the half-life of (38Sulphur) is 2.48 Hours while (38Argon) is a stable nuclei. We have 100 atoms from each at 5 pm. We look at them again after an hour. We still have 100 Argon atoms. Between Sulphur and Chlorine which is now available in less number?

PART-II

Total 42 marks (Optional, 6 out of 9)

Each carry 7 marks, answer only two from each section

SECTION-A

## Each carry 7 marks, answer only two                                                                                       (7×2)

Question 3 [4+3]

Derive the Electric Field Vector E for the Dipole Vector P a) E|| ;in a direction of alignment with the Dipole Vector, also called End-On configuration b) E^; in a direction perpendicular to the Dipole, also called Broad-on configuration.

Question 4 [4+3]

Derive the Electric Field Scalar Potential V for the Dipole Vector P a) V|| ; in a direction of alignment with the Dipole Vector, also called End-On configuration b) V^; in a direction perpendicular to the Dipole, also called Broad-on configuration.

Question 5 [1+2+4]

Define Electric flux F (Phi) in 1 or 2 lines and write out expression for it for a uniform electric field E. State and explain Gauss Law in terms of charge and flux. State the mathematical vector form of Coulomb’s law of electrostatics force and derive the same from Gauss Law.

SECTION-B

## Each carry 7 marks, answer only two.                                  (7×2)

Question 6 [2+3+2]

Obtain an expression for the Nuclear Size of an atom by solving for distance of closest approach (r) which is also known as Impact Parameter (say l). Use an incoming alpha-particle of mass mα and charge q that’s deflected by the presence of a nucleus of atomic number Z to obtain l. Now replace the variables by some numerical: mα = 6.8×10-27kg, e = 1.6 x 10-19 coul, Z=14, and vα= 2.0×107 m/s. Express the answer in Femto-meters.

Question 7 [3+4]

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

Question 8 [5+1+1]

Derive the Radioactive Decay Law and define half-life. Give example of two radioactive elements. The decay half-life of proton is ~1030 years. Explain if this is important to our existence as living organisms.

SECTION-C

## Each carry 7 marks, answer only two.                                  (7×2)

Question 9 [breakdown of marks 5+2]

Describe the Rutherford model for atom and point out its two drawbacks.

Question 10 [breakdown of marks  2+2+3]

Describe Nuclear Fusion and Fission in less than 3 sentences each. What’s the cause of Sun’s energy, Fusion or fission? What about the stars Alpha-centauri? Write the charge and mass of each of these elementary particles. Photon, alpha-particle, gamma-rays, neutrino, proton, electron, in a table.

Question 11 [breakdown of marks 1+3+3]

Write the concept of Binding Energy. Write out the famous Einstein’s mass-energy equivalence relation. Explain why the mass of individual protons, neutrons and electrons when added together surpass that of the mass of the atom. Write a short description of the principle behind Nuclear Reactor.