 CBSE [All India]-Set-2-2007

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• Q1

Ultraviolet radiations of different frequencies and are incident on two photosensitive materials having work functions W1 and W2 (W1>W2) respectively. The kinetic energy of the emitted electrons is same in both the cases. Which one of the two radiations will be of higher frequency?

Marks:1 • Q2

Define the term ‘activity’ of a radionuclide. Write its SI unit.

Marks:1

The number of radioactive disintegrations taking place per second for a given sample is called as the activity of that sample.
Its SI unit is bequerel.

• Q3

An electron is moving along +ve x-axis in the presence of uniform magnetic field along +ve y-axis. What is the direction of the force acting on it?

Marks:1

The direction of force acting on it will be along the –ve z-axis.

• Q4

What should be the length of of dipole antenna for a carrier wave of frequency 6 108 Hz ?

Marks:1 • Q5

What should be the length of dipole antenna for a carrier wave of frequency 5 108 Hz?

Marks:1

Length of dipole antenna • Q6

A voltage of 30 V is applied across a carbon resistor with first, second and third rings of blue, black and yellow colours respectively. Calculate the value of current, in mA, through the resistor.

Marks:2

First of all we have to find the value of current, which can be given by, From the colour coding technique the value of R is V=30 V.

Therefore current flowing through the resistor is given by • Q7

Calculate the current drawn by the primary of a transformer which steps down 200V to 20V to operate a device of resistance 20 . Assume the efficiency of the transformer to be 80%.

Marks:2

Given that The current flowing through the primary of transformer is given by, The efficiency of the transformer is given by, Substituting the required values in the above equation we get, • Q8

An a.c. voltage of 100V, 50 Hz is connected across a 20ohm resistor and 2 mH inductor in series. Calculate (i) impedence in the circuit, (ii) rms current in the circuit.

Marks:2

The impedance of the circuit is given by the relation, • Q9

Define resolving power of compound microscope. How does the resolving power of a compound microscope change when
(i) Refractive index of the medium between the object and objective lens increases?
(ii) Wavelength of the radiation used is increased?

Marks:2

Resolving power of a compound microscope is defined as the reciprocal of the smallest distance between two point objects which can just be resolved when seen through the microscope. (i) The resolving power is directly proportional to the refractive index( ) of the medium so, it increases with increase in the refractive index ( ) of the medium between the object and objective lens.
(ii) The resolving power is inversely proportional to the wavelength ( ) of the radiation and so, it decreases with increase in wavelength ( ), of the radiation. 