## Saturday, 26 July 2014

### CLASS 12 PHYSICS TEST PRACTICE 3

Practice Test Paper 3

Physics (Theory) – XII

Time allowed: 3 hours                                                                                                 Maximum marks: 70  Q. 1.
An electron and a proton, moving parallel to each other in the same direction with equal momenta, enter into a uniform magnetic field which is at right angles to their velocities. Trace their trajectories in the magnetic field.

1
Q. 2.
Two identical loops, one of copper and another of constantan are removed from a magnetic field within the same time interval. In which loop will the induced current be greater?

1
Q. 3.
The power factor of an a.c. circuit is 0.5. What will be the phase difference between voltage and current in this circuit?

1
Q. 4.

# Does the ‘stopping potential’ in photoelectric emission depend upon

(a)    the intensity of the incident radiation in a photocell?
(b)   The frequency of the incident radiation?

1
Q. 5.
What is the function of ‘cladding’ in a typical optical fibre?

1
Q. 6.
(a)    Draw the graphs showing variation of inductive reactance and capacitive reactance with frequency of applied a.c. source.

(b)   Can the voltage drop across the inductor or the capacitor in a series LCR circuit be greater than the applied voltage of the a.c. source? Justify your answer.

2
Q. 7.
Define electric field intensity. Write its S.I. unit. Write the magnitude and direction of electric field intensity due to an electric dipole of length 2a at the mid-point of the line joining the two charges.

2
Q. 8.
State the underlying principle of a transformer. Write two causes of power loss in it.

2
Q. 9.
Two dielectric slabs of dielectric constant K1 and K2 are filled in between the two plates, each of area A, of the parallel plate capacitor as shown in the figure. Find the net capacitance of the capacitor.  d 2
Q. 10.
Explain the term remote sensing in communication. Name the satellite used for this purpose.

2
Q. 11.
With the help of diagrams distinguish between forward biasing and reverse biasing of a p-n junction diode.

2
Q. 12.
Monochromatic light is refracted from air into glass of refractive index n. Find the ratio of wavelengths of the incident and refracted light.

2
Q. 13.
An electric dipole is held in a uniform electric field. (a) using suitable diagram, show that it does not undergo any translatory motion, and (b) derive an expression for the torque acting on it and specify its direction.

3
Q. 14.
Explain, with the help of diagram, the principle and working of an a.c. generator. Write the expression for the e.m.f. generated in the coil in terms of its speed of rotation.

3
Q. 15.
Define the term ‘temperature coefficient of resistivity’. Write its SI unit. Plot a graph showing the variation of resistivity of copper with temperature.

3
Q. 16.
Draw a labelled diagram of a moving coil galvanometer. Explain its working principle. Can this galvanometer be used to detect an a.c. in a circuit? Give reason.

3
Q. 17.
A battery of emf 10 V and internal resistance 3Ω is connected to a resistor R.

(a)    If the current in the circuit is 0.5 A, calculate the value of R.
(b)   What is the terminal voltage of the battery when the circuit is closed?

3
Q. 18.
Draw a labelled diagram of experimental setup of Rutherford’s alpha particle scattering experiment. Write two important inferences drawn from this experiment.

3
Q. 19.
With the help of a labeled diagram explain in brief the working of a cyclotron.

3
Q. 20.
Calculate the binding energy per nucleon (in MeV) for and . Comment on the difference of these binding energies and its significance in relation to a-decay of the nuclei. Given: mass of = 1.00783 u, mass of = 1.00867 u, mass of = 3.01664 u, mass of = 4.00387 u.

3
Q. 21.
A ground receiver station is receiving a signal at (a) 5 MHz and (b) 100 MHz, transmitted from a ground transmitter at a height of 300 m located at a distance of 100 km. Identify whether it is coming via space wave or sky wave propagation or satellite transponder. (Given the value of radius of the earth is 6400 km and maximum electron density, Nmax = 1012 m-3)

3
Q. 22.
(a)    Draw the energy level diagram showing the emission of b-particles followed by g-rays by a .
(b)   Plot the distribution of kinetic energy of b-particles and state why the energy spectrum is continuous.

3
Q. 23.
Name the constituent radiation of electromagnetic spectrum which
(a)    is used in satellite communication.
(b)   is used for studying crystal structure.
(c)    is similar to the radiations emitted during decay of radioactive nuclei.
(d)   has its wavelength range between 390 nm and 770 nm.
(e)    is absorbed from sunlight by ozone layer.
(f)    produces intense heating effect.

3
Q. 24.
Explain, with the help of a circuit diagram, how the thickness of depleteion layer in a p-n junction diode changes when it is forward biased. In the following circuits which one of the two diodes is forward biased and which is reverse biased?   -10V    (a)  (b)  -10 V
3
Q. 25.
Draw a level diagram of a Van de Graaff generator. Give its principle and explain its working.

Or

Define capacitance of a capacitor. Give its S.I. unit. Prove that the total electrostatic energy stored in a parallel plate capacitor is CV2 and hence find the expression for the energy density of the capacitor.

5
Q. 26.
(a)    Define the term ‘impedance of series LCR circuit’. Derive a mathematical expression for it using Phasor diagram.

(b)   Obtain the resonant frequency of a series LCR circuit with L = 2.0 H, C = 32 mF and R = 10 Ω

Or

(a)    Distinguish between the terms resistance, reactance and impedance of an a.c. circuit.
(b)   A 100 mF capacitor in series with a 40 Ω resistance is connected to a 100 V, 60 Hz supply. Calculate (i) the reactance, (ii) impedance, and (iii) maximum current in the circuit.

5
Q. 27.
Using Huygen’s principle, draw a diagram to show propagation of a wavefront originating from a monochromatic point source.
Describe diffraction of light due to a single slit. Explain formation of a pattern of fringes obtained on the screen and plot showing variation of intensity with angle q in single slit diffraction.

Or

What is meant by a linearly polarized light? Which type of waves can be polarized? Briefly explain a method for producing polarized light.
Two polaroids are placed at 90o to each other and the intensity of transmitted light is zero. What will be the intensity of transmitted light when one more polaroid is placed between these two bisecting the angle between them? Take intensity of unpolarised light as I.

5