**Model Sample Paper - 6 **

Q.1. Name two physical conditions on which
the resistivity of a metal depends.

Q.2.Why does the picture on a TV screen
become distorted when a magnet is brought near the screen?

Q.3.Does a beam of white light give a
spectrum on passing through a hollow prism?

Q.4.Why do we prefer a choke to a rheostat in
controlling current in a.c. circuit?

Q.5.The standard resistance coils are made of
manganin. Why ?

Q.6.When light undergoes reflection what
happens to (a) frequency (b) wavelength of light ?

Q.7.There are certain types of stars called
variable stars which undergo periodic change in their light output. If such a
star doubles its light output, how much does its magnitude change?

Q.8.What is the reactance of an inductor in a
D.C. circuit?

Q.9.State Hubble's law. What is the
significance of Hubble's constant?

Q.10.An applied voltage signal consists of a
superposition of a D.C. voltage and an a.c. voltage of high frequency. The
circuit consists of an inductor and a capacitor in series. Show that D.C.
signal will appear across C and the a.c signal across L.

Q.11.A loop of irregular shape is made of a
flexible wire and placed in an external field. What shape the loop acquires
when a current is passed though it? Explain.

Q.12.State the conditions which must be
satisfied for two light sources to be coherent.

Q.13.Long distance radio broadcasts use short
wave bands, why?

Q.14.A ray of light falls normally on one
face of a prism of angle 45^{0}. If critical angle for materiel of
prism is 45^{0}, trace the course of rays. Calculate m ?

Q.15.An object of size 3 cm is placed 14 cm
in front of a concave lens of focal length 21 cm. Describe the image produced
by the lens. What happens of the object is moved farther from the lens?

Q.16. State Coulomb's law of magnetostatics.
What is the constant of proportionality in S.I. units and give its value.

Q.17. Obtain the binding energy of the
nucleus, _{26}Fe^{56} in units of MeV from the following data m_{H}
= 1.007825 a.m.u. m_{n} = 1.0086659 a.m.u. m[_{26}Fe^{56}]
= 55.934939 a.m.u., 1amu = 931.5 MeV.

Q.18. In a transistor, base is made thin and
doped with little impurity atoms. Why?

Q.19. Explain through a labelled circuit
diagram the working of p-n-p transistor as common base amplifier.

Q.20. An electron moves a distance of 6 cm
when accelerated through from rest by an electric field of strength of 2 x 10^{4}
N/C. Calculate the time of travel. Given mass of electron 9 1 X 10^{-31}
kg.

Q.21. If a current of 2 A be passed through a
copper voltammeter for 2 hours the amount of copper deposited is 4.5 g.
Calculate electrochemical equivalent of nickel when the atomic weights of
copper and nickel are 63.5 and 58.7 respectively.

Q.22. Derive an expression for resistivity of
the material of a given conductor in terms of relaxation time.

Q.23. Discuss the important properties of
nuclear forces.

Q.24. Discuss communication of T.Y. video
signals of high frequency using high T.V. tower. Deduce an expression for the
maximum area over which a signal can be sent on earth by ground wave if an
antenna of height h is used to transmit the signal.

Q.25. In the following figures which of the
diodes are forward biased and which are reverse biased?

Q.26.A galvanometer has a resistance of 50
ohms and gives full-scale deflection with a current of 50 mA. Calculate
resistance required to measure 10 Ampere current.

Q.27.A long wire is best as shown in figure.
What will be magnitude and direction of magnetic field at the center **O**
if a current of 2 A is passed through the wire? Radius of circular path is lm
and the straight wire does not touch circular loop.

Q.28. Calculate electric field due to a
dipole at a point on its axis and at a distance d from its centre. OR A loop of
wire of negligible thickness has a radius r and charge q is uniformly
distributed over the loop. Find the electric field E at a point P situated at a
distance x from its center.

Q.29. Describe Millikan's method for
determination of electronic change on electron.

Q.30.A 25 0 m F capacitor,
a 0.1 0 henry inductor and a 25.0 ohm resistor are connected in series with an
a.c. source whose e.m.f is given by E = 310 sin 314t. (i) What is the frequency
of the e.m.f.?(ii) Calculate

(a) the reactance of the circuit (b) the
impedance of the circuit (c) Current in the circuit.

Figs Q25&28