# CBSE [All India]-Set-2-2004

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• Q1

Marks:1

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:1

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:1

The rms value of e.m.f is given by the relation,

E r.m.s = Eo

• Q4

Draw the voltage current characteristic of a zener diode.

Marks:1

The voltage current characteristics of a zener diode is given below,

• Q5

Two metals A and B have work functions 4 eV and 10eV respectively. Which metal has higher threshold wavelength?

Marks:1

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:2

The logic symbol for OR gate is given below,

• 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:2

(i) The torque of the dipole is given by the relation,

= pE sin

= (q 2a)E sin

Substituting the given values in the above equation we get,

(ii) Potential energy of the dipole is given by,

• Q8

Explain how does the resistivity of a conductor depend upon (i) number density ‘n’ of free electrons, and (ii) relaxation time ’.

Marks:2

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:2

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:2