SUB: PHYSICS MARKS: 50

CLASS: II ISC TIME: 1.5 Hrs

**PART-A**

**Total 10 marks **(**Compulsory, short-answer questions**)

## Each carry 1 mark. Answer all. (10)

**Question 1 **

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

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

(c) Say if this is correct or incorrect: “Between an alpha-particle and a proton the alpha particle has more electrostatics potential energy in an electrostatics potential of 100 volt.”?

(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 (** ^{38}Chlorine**) is 0.62 hours and the half-life of (

**) is 2.48 Hours while (**

^{38}Sulphur**) is a stable nuclei. We have**

^{38}Argon**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?

(i) Give example of two fissionable materials which can be used for atomic weapon. Give the approximate size of energy output of some Indian reactors.

(j) If (Total energy released in fission) = (Total number of fissionable atoms) x (energy released per atom), then, calculate the Total energy released by 1 kilo gram of ^{235}U_{92}, Hint: Use **Avogardo Number**. _{ }^{ }

**PART-II**

**Total 40 marks **(**Optional, 5 out of 9, Long-answer questions**)

SECTION-A

## Each carry 8 marks, answer only two (8×2)

**Question 2**

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 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 4**

Define **Electric flux ****F (Phi)** in 1 or 2 lines and write out expression for it for a uniform** electric field E**. State **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 8 marks, answer only one. (8×1)

**Question 5**

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 m_{α} 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: m_{α = }_{6.8×10}^{-27}kg, e = 1.6 x 10^{-19 }coul, Z=14, and v_{α}= 2.0×10^{7} m/s. Express the answer in Femto-meters.

**Question 6 **

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**} energy of the Hydrogen-atom.

SECTION-C

## Each carry 8 marks, answer only one. (8×1)

**Question 7**

Derive the **Radioactive Decay Law** and define **half-life**. Give example of two radioactive elements. The decay half-life of proton is ~10^{30 }years. Explain if this is important to our existence as living organisms.

** **

**Question 8 **

Derive the expression for the **energy E of a cyclotron** by applying the **equation of motion of an ion with charge q, mass m in a magnetic field B**. Hint: Use **Lorentz Force** on a charge and Kinetic Energy.

SECTION-D

## Each carry 8 marks, answer only one. (8×1)

**Question 9**

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 10 **

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.