WBCHSE 2015 Question Paper

GROUP-B

Answer the following question in short (Alternatives are to be noted):            [2 x 5=10]

 

 

1. Establish the relation between drift velocity of electron and alternating current.    
   

   Or, Why is potentiometer preferred to voltmeter for the measurement of emf of a cell ? Explain.    2
   

2. How the galvanometer is converted into a voltmeter ?
   

   Or, The plane of a suspended current carrying rectangular coil makes an angle θ with the direction of uniform magnetic field. Calculate the torque acting on the coil.
   

3. An electromagnetic wave of frequency 25MHz travels in free space along x-direction. At a particular point in space and time, V/m. What is the value and direction of of the wave at that point?    1+1
   
4. Draw the variation of binding energy per nucleon with mass number of atoms and indicate the stable and unstable region on the diagram.     1+1
   

   Or,
   

   State Bohr's quantum condition in connection with the H-atom.
   

   What is the value of Bohr's radius in SI system?    1+1
   

5. Write down different modes by which EM waves can propagate from transmitting antenna to receiving antenna. Mention one important use of microwaves.     1+1
   

   Or,
   

   Draw a neat diagram of amplitude modulated waveform. Write down the expression of 'modulation index' and show each term in the diagram.    1+1
   

   
    

GROUP-C

Answer the following question in short (Alternatives are to be noted):            [3 x 9=27]

 

1. Define electric dipole moment. Find the torque acting on a dipole when it is placed in a uniform electric field .                                                    1+2
   

   Or,
   

   State Gauss's theorem in electrostatics. Find the electric flux through a surface of area 50 m² in x-y plane in the electric field Vm^-1.                                    1+2
   

2. What is understood by capacitance of a capacitor? A 900 pF capacitor is charged to 100 V by battery. How much energy is stored in the capacitor ?                                    1+2
   
3. Define angle of dip at a place. What will be the value of the angle of dip at the poles and at the equator of the earth ? At what place on the earth's magnetic field and its vertical component be equal ?     1+1+1
   

   Or,
   

   State Ampere's circuital law. Using this law obtain an expression for the magnetic field on the axis of a toroidal solenoid for a current of i A.                                    1+2
   

4. What are coherent sources? Green light of wavelength 5100 Å is incident on a double slit. If the overall separation of 10 fringes on a screen 200 cm away from the slits is 2 cm, find the distance between the slits.    1+2
   

   Or, What is understood by diffraction of light ? In a single slit experiment, if the width of the slit increases, what will be the change of angular width of central maxima ? State Brewster's law.    1+1+1
   

5. The refracting angle of an equilateral prism is A. Derive an expression for the angle of deviation for a ray of light incident on the refracting surface of the prism. Draw a neat curve to show the variation of deviation with angle of incidence of the incident ray.
   

   Or, Calculate the speed of light in a medium whose critical angle is 45⁰. Mention two practical applications of opticle fibre.    2+1
   

 

1. What is meant by stopping potential in photoelectric emission ? Does the stopping potential depend on i) the intensity and, ii) the frequency of the incident light? Explain.    1+1+1
   

   Or, what conclusion is drawn from Davisson-Germer experiment? Are matter waves electromagnetic waves? Explain.
   

2. State radioactive decay law. Write down the relation between radius of the nucleus and mass number of an atom. What is isotone? Give an example.    1+1+1
   
3. Draw the I-V characteristics of a LED and explain its working principle.     1+2
   

   Or, Draw the output characteristics of an n-p-n transistor in CE configuration for five base currents. What is an oscillator?
   

4. What is NOR gate? Prepare its Truth table. Why it is called universal gate?     2+1
   

   Or, What is Zener diode? Draw its voltage vs current characteristics in the reverse breakdown voltage and indicate the breakdown voltage on the characteristics. Mention one important use of this diode.    1+1+1
   

   
    

GROUP – D

Answer the following question in short (Alternatives are to be noted):             [5x3=15]

1. 
    
   1. Whith the help of a circuit diagram explain the function of a shunt used in a galvanometer.
      
   2. State Kirchhoff's laws in a network of conductors carrying current. State which laws obeys the principle of conservation of energy.                                         2+(2+1)
      

   Or,
   

   1. Establish the balanced condition of Wheatstone's bridge applying Kirchhoff's laws.
      
   2. Length, diameter and specific resistance of two wires of different materials are each in the ratio 2:1. One of the wires has a resistance of 10 ohm. Find the resistance of the other wire.                3+2
      
2. 
    
   1. State Fleming's right hand rule. Define self-inductance of a coil. Explain non-inductive coil with diagram.
      
   2. A metallic disc of radius 10cm is rotating uniformly about a horizontal axis passing through its center with angular velocity 10 rev.s^-1 . A uniform magnetic field of intensity 10^-2 Tesla acts along the axis of the disc. Find the potential difference induced between the center and the rim of the disc.        (1 +1 +1)+2
      

   Or,
   

   1. The instantaneous voltage from an AC source is given by e = 200 sin 314t volt. Find the R.M.S. voltage. What is the frequency of the source?
      
   2. State the condition under which phenomenon of resonance occurs in series LCR circuit when AC voltage is applied. In a series LCR circuit, the current is in same phase with voltage. Calculate the value of self-inductance if the capacitor used is 20 µF and resistance used is 10 ohm with the AC source of frequency 50 Hz.                                                 2 + (1+2)
      
3. 
    
   1. Focal length of two thin lenses kept in contact are f₁ and f_2. Prove that their equivalent focal length f is given by .
      
   2. The refracting angle of a prism is 60⁰ and the refractive index of its material is . Find the minimum angle of incidence of a ray of light falling on one refracting face of the prism such that the emerging ray will graze the other refracting face.                                        2+3
      

   Or,
   

   1. The object and the image are at distance x and y respectively from the focus of a concave mirror. Establish the relation between x, y and the focal length f of the mirror.
      
   2. Light from a point source placed at the bottom of a rectangular glass slab of thickness 5cm is internally reflected by the upper surface and a circle of radius 8 cm is formed at the bottom. Find the R.I. of glass.     2+3

Magnetism and Electro-Magnetism

Term	Point Definition
Magnet:	It is a substance mainly Iron Oxide which has the ability to attract iron dust, attractive or repulsive property, and directive property.
Magnetic Di-poles:	The system of two opposite and equal strong poles separated be a small distance is known as Magnetic Dipoles.
Magnetic Field:	The area around which the magnetic force of interaction can be experienced is known as Magnetic field. It also may be defined as the region in which Magnetic effect due to a magnet can be detected is called its magnetic field.
Intensity of Magnetic Field:	The magnetic field intensity at a point is force experienced by per unit N-pole at that point. [N.B.     Field intensity, Intensity of field, Field strength or simply Field is all synonymous. Most time we define field intensity as force experienced by a unit N-Pole, but it's better to write force experienced by per unit N-pole.]
Magnetic Permeability:	The ability of a substance to magnetize in a magnetic field is known as its permeability and denoted by µ.It also may be defined as extent of magnetization per unit magnetic field.
Magnetic Reluctance:	The ability of substance to prevent magnetization in a magnetic field.     It is reciprocal of magnetic Permeability, and is also defined as required magnetic field per unit magnetization. [N.B.    Magnetic Permeability & Magnetic Reluctance both are similar to electric Conductivity and Resistivity. But they are not remain always constant like them.]
Magneto-Motive Force (M.M.F.):	The work done in moving the unit N-Pole through a magnetic circuit is known as the M.M.F. of that cicuit.
Magnetic Potential:	At a point it is defined as the work done in bringing a unit N-pole from infinity to that point. At a point Magnetic Potential is distance integral of field intensity from the source.
Ferro-Magnetic Substance:	It is the substance which is largely attracted even in feeble magnetic field. These have high permeability values.
Para-magnetic Substances:	These are the substances which are feebly attracted by magnetic field.
Dia-Magnetic Substances:	The substances which are feebly repelled by the magnetic field.
Retentivity:	The ability of a ferromagnetic substance to retain its magnetization even the external applied field is removed.