# CBSE [All India]-Set-1-2004

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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

A solenoid with an iron core and a bulb are connected to a d.c source. How does the brightness of the bulb changes, when the iron core is removed from the solenoid?

Marks:1

Since the inductive reactance for d.c current is zero, the brightness of the bulb remains unchanged.

• Q5

Draw the voltage current characteristic of a zener diode.

Marks:1

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

• Q6

A circular coil of100 turns, radius 10 cm carries a current of 5 A. it is suspended vertically in a uniform horizontal magnetic field of 0.5 T, the field lines making an angle of 600 with the of the plane of the coil. Calculate of the torque must be applied on it to prevent it from turning.

Marks:2

Given, N = 100, r = 10cm, I = 5A, B=0.5T.

Also, = 900 - 600 = 300.

The required magnitude of torque is given by the relation,

• Q7

A T.V. tower has a height of 400 m at a given place. Calculate as coverage range, if the radius of the earth is 6400 km.

Marks:2

The coverage range is given by the relation,

• Q8

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,

• Q9

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.

• Q10

Give the logic symbol for an AND gate. Draw the output wave form for AND gate for input wave forms A and B.

Marks:2