1. Xtra Edge February 2012 - Career Point

14. Derive the expression for the capacitance of a
parallel plate capacitor, having two identical plates
each of area A and separated by a distance d, when
the space between the plates is filled by a dielectric
medium.
15. In a meter bridge shown in circuit diagram, the
balance point is found to be at 40 cm from the
end A when resistor Y is of value 20 Ω.
Calculate the shifting in of balancing point on the
same wire if X and Y are interchanged.
X Y
A
D
B
G
E
16. Two parallel wires of infinite length have linear
charge densities λ1 and λ2 coulomb/metre. Derive an
expression for force per unit length acting between
them.
17. A 10 µF capacitor is charged by a 30 V d.c. supply
and then connected across an uncharged 50 µF
capacitor. Calculate (i) the final potential difference
across the combination and (ii) the initial and final
energies. How will you account for the difference in
energy ?
18. Amplitude of electric field in an electromagnetic wave
is 3×10 6 V/m. Find amplitude of magnetic field.
19. Explain it
(i) work function
(ii) Threshold frequency
(iii) Threshold wave length
(iv) Stopping potential
20. Show that the energy of the first excited state of He +
atom is equal to the energy of the ground state of
hydrogen atom
21. In a young's double slit experiment, the slits are
separated by 0.56 mm and the screen is placed 2.8 m
away. The distance between the central bright fringe
and the fifth bright fringe is measured to be 1.5 cm.
Determine the wavelength of light used in the
experiment.
22. A communication system having operating wavelength
λ in m can use only x% of its source frequency as its
channel bandwidth. The system is to be used for
transmitting TV signals requiring bandwidth of F Hz,
How many channels can this system transmit
simultaneously
C
23. The given figure shows a network of resistances R1,
R2, R3 and R4. Using Kirchhoff's laws, establish the
balance condition for the network.
B
A G C
XtraEdge for IIT-JEE 69 FEBRUARY 2012
R1
R2
R3 R4
D
+ –
24. Distinguish between resistance, reactance and
impedance for an a.c. circuit. Draw graph showing
variation for reactance of (i) a capacitor (ii) an
inductor with frequency of the circuit.
25. A 0.5 m long metal rod PQ completes the circuit as
shown. The area of the circuit is perpendicular to the
magnetic field of flux density 0.15 T. If the
resistance of the total circuit is 3 Ω. Calculate the
force needed to move the rod in the direction as
indicated with speed 2 ms –1 .
× × × × × ×
Q
× × × ×
× × × × × × × × × ×
× × × × × × × × × v ×
× × × × × × × × × ×
× × × × × × P × × × ×
26. Explain the principle and working of cyclotron with
the help of a labelled diagram.
27. Using Gauss' theorem, deduce an expression for the
electric field intensity at any point due to a thin,
infinitely long wire of charge/length λ C/m.
28. What is diffraction ? write down its difference with
interference ? If single slit diffraction is obtained by
using light of wavelength 5000Å and slit width 0.5
mm. Then calculate angular width of central
maxima.
OR
What is dispersion ? How the angular dispersion is
defined ? Which colours is deviated maximum by a
prism ? Calculate dispersive power of crown glass if
refractive indices for red, yellow and violet colours
are 1.5140, 1.5170 and 1.5318 respectively.
• 29. What is spectrum ? write down types of spectrum
?
• OR
• If electrons trans it from first excited state of
H-atom to ground state and emitted radiations
incidents over a metallic surface of threshold
wavelength 4000 Å, then what is the value of