# CBSE [All India]-Set-1-2007

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• Q1

In a series LCR circuit, the voltages across an inductor, a capacitor and a resistor are 30 V, 30 V and 60 V respectively. What is the phase difference between the applied voltage and the current in the circuit?

Marks:1

The phase difference can be given by the relation,

• Q2

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

• Q3

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.

• Q4

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.

• Q5

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

Marks:1

• Q6

Two point charges 4 C and -2 C are separated by a distance of 1 m in air. Calculate at what point on the line joining the charges is the electric potential is zero.

Marks:2

Let the potential be zero at distance 'x' from the charge of C . The arrangement is shown in figure below,

According to the given condition,

V1 + V2 = 0

Substituting the values for V1 and V2 we get,

• Q7

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

• Q8

A galvanometer has a resistance of 30 . It gives full scale deflection with a current of 2mA. Calculate the value of the resistance needed to convert it into an ammeter of range 0-0.3A.

Marks:2

We have the relation,

Substituting the required values in the above equation we get,

• Q9

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,

• Q10

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,