PHYSICS – 2003 ,PAPER I, SECTION B

                          Time Allowed: Three Hours    Maximum Marks: 200

 

Candidates should attempt Questions 1 and 5 which are compulsory, and any Three of the remaining questions selecting at least ONE question from each Section.

SECTION B

5.        Answer any four of the following:

(a)    If in the LCR series circuit, a.c. voltmeter reads 30 volt across the resistor, 80 volt across the inductance, 40 volt across the condenser, what is the applied e. m.f.?

(b)   A condenser of capacity 1 microfarad and inductance of 0.2 Henri and Resistance of 800 ohm are joined in series is the circuit oscillatory?

(c)    An electric dipole of two opposite charges of 10⁻⁴ coulomb separated by 4 cm placed in an external electric field of strength 10 ⁻⁶ volts/m. find the work required to turn the dipole in the reverse direction.

(d)   What is the physical significance of pointing vector? Deduce an expression for the intensity of electromagnetic wave propagating in free space.

(e)    Two magnets having magnetic moments M and 3M are joined to form a cross. If this combination is suspended freely in a uniform horizontal magnetic field, what will be its equilibrium orientation in this field?

6.       (a) Write down the Poisson’s equation for a homogeneous dielectric medium. What is the condition necessary to derive Laplace equation from Poisson’s equation?

             A 50 volt AC source of frequency 500 Hz is connected to an LCR circuit with L = 8.1 milihenri; C= 12.5 µ F; R = 20Ω; all connected in series. Find the potential across the resistance.

                  (b) State Kirchoff’s laws for steady currents and prove them.

Apply the Kirchoff’s laws to whetstones’ network and show that P/ Q = R/S

7.       (a) Using Maxwell’s equations, obtain the velocity of an electromagnetic wave in vacuum.

                   (b)  what is Wien’s displacement law? Show that sun radiates maximum energy in the visible region whereas earth radiates in IR region.

8.       (a) (i) Derive the equation of state for a van der Wall’s gas and calculate values of critical constants.

                        (ii) What is entropy? How is it related to disorder in the system?

               (b) Discuss Einstein’s Theory of specific heat of solids Compare and contrast with Debye’s theory.

USEFUL CONSTANTS

 h= 6.62 x 10⁻³⁴ joule –sec.

e= 1.6 x 10⁻¹⁹ coulomb

c= 3.0 x 10⁸ m/ sec.

1 eV = 1.6 x 10⁻¹⁹ joule

1/4 ԑₒ = 9 x 10⁹ Nm² / coulomb

µₒ = 4  x 10⁻⁷ Weber / amp.m