CBSE [All India]-Set-2-2004
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Q1
Why is shortwave band used for long distance radio broadcast? Marks:1View AnswerAnswer:
Shortwave band is used for long distance radio broadcast since it can be easily reflected back to earth by ionosphere layer of our atmosphere. -
Q2
Two metals A and B have work functions 2eV and 5eV respectively. Which metal has lower threshold wavelength? Marks:1View AnswerAnswer:
The work function of a metal is inversely proportional to the threshold frequency that is,
o
[1/W]
Hence metal with work function 5eV(metal B) will have lower threshold frequency. -
Q3
Peak value of emf of an a.c. source is E0. What is its r.m.s. value? Marks:1View AnswerAnswer:
The rms value of e.m.f is given by the relation,
E r.m.s
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Q4
Draw the voltage current characteristic of a zener diode. Marks:1View AnswerAnswer:
The voltage current characteristics of a zener diode is given below,
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Q5
Two metals A and B have work functions 4 eV and 10eV respectively. Which metal has higher threshold wavelength? Marks:1View AnswerAnswer:
The work function of a metal is inversely proportional to the threshold frequency that is,
o[1/W]Hence metal with work function 4eV(metal A) will have greater threshold frequency. -
Q6
Give the logic symbol for an OR gate. Draw the output wave form for input wave forms A and B for this gate. 
Marks:2View AnswerAnswer:
The logic symbol for OR gate is given below,
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Q7
An electric dipole of length 4 cm, when placed with its axis making an angle of 600 with a uniform electric field experiences a torque 4(3)1/2 of Nm. Calculate the (i) magnitude of the electric field. (ii) potential energy of the dipole, if the dipole has charges of 
8nC. . Marks:2View AnswerAnswer:
(i) The torque of the dipole is given by the relation, 
= pE sin
= (q 
2a)E sinSubstituting the given values in the above equation we get, 
(ii) Potential energy of the dipole is given by, 
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Q8
Explain how does the resistivity of a conductor depend upon (i) number density ‘n’ of free electrons, and (ii) relaxation time ’. Marks:2View AnswerAnswer:
The resistivity of the conductor is given by the relation,
= m / (n e2)
(i) From the above equation it follows that resistitvity of a given conductor is inversely to the number density ‘n’ of free electrons.
(ii) The resistivity of the conductor increases with decrease in relaxation time and vice-versa. This is because it is inversely proportional to relaxation time. -
Q9
Two long parallel straight wires X and Y separated by a distance of 2.5 cm in air carry currents of 5 A and 2.5 A respectively in opposite directions. Calculate the magnitude and direction of the force on a 10cm length of the wire Y. 
Marks:2View AnswerAnswer:
The magnitude of force is given by relation,
Here the direction of force is perpendicular to wire Y and it acts away from it. -
Q10
Explain, with the help of graph, the variation of conductivity with temperature for a metallic conductor. Marks:2View AnswerAnswer:
Resistivity of metal will decrease with increase in temperature. This is because free electrons collide more frequently with positive metal ions, which results in decrease of relaxation time. This ultimately decreases the conductivity of metal.
= m/(ne2)
