 # CBSE [All India]-Set-2-2016

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• Q1

In what way is the behaviour of a diamagnetic material different from that of a paramagnetic, when kept in an external magnetic field?

Marks:1

When a bar of diamagnetic material is placed in an external magnetic field, the field lines are repelled or expelled and the field inside the material is reduced.

Whereas when a paramagnetic material is placed in an external magnetic field, the field lines are attracted towards it. Thus the field lines get concentrated inside the material and the field inside is enhanced.

• Q2

The plot of the variation of potential difference across a combination of three identical cells in series, versus current is shown below. What is the emf and internal resistance of each cell?

Marks:1

Let E and r be the EMF and internal resistance of all cells respectively and e and r' be the EMF and internal resistance of each cell respectively.

According to the definition of the terminal potential difference,

V = E − Ir

E is the EMF and r is the total internal resistance of the circuit.

I = 0 V = E

From the graph we can see

E = 6 V

As there are three cells we can write,

E = 3 × e e = 2 V

And, when, V = 0

E = Ir

As per the question the cells are connected in the series, so we can write.

• Q3

Why does sun appear red at sunrise and sunset?

Marks:1

At the time of sunset or sunrise, the Sun and its surroundings appear red because of the scattering of light. At the time of sunset or sunrise, the light rays from the Sun have to travel a long distance to reach our eyes through the Earth's atmosphere. In other words, we can say that when we look towards horizon, we are looking through more of Earth’s atmosphere than when we look overhead. The light reaching our eyes is rich in red colour as blue light is largely scattered away by the particles present in the Earth's atmosphere.

• Q4

A charge 'q' is moved from a point A above a dipole of dipole moment 'p' to a point B below the dipole in equatorial plane without acceleration. Find the work done in the process.

Marks:1

The net force on the charge q is directed parallel to the dipole and hence perpendicular to its motion along AB.

Work done = 0

• Q5

Name the essential components of a communication system.

Marks:1

Communication is the act of transmission of information.

Communication system has three essential components − transmitter, medium channel, and receiver.

• Q6

Calculate the de-Broglie wavelength of the electron orbiting in the n = 2 state of hydrogen atom.

Marks:2

• Q7

A battery of emf 12 V and internal resistance 2 Ω is connected to a 4 Ω resistor as shown in the figure.

(a) Show that a voltmeter when placed across the cell and across the resistor, in turn, gives the same reading.

(b) To record the voltage and the current in the circuit, why is voltmeter placed in parallel and ammeter in series in the circuit?

Marks:2

(a) According to the definition of terminal potential difference,

E = V + Ir

V = E – Ir

E = 12 V, r = 2 Ω

V = 12 – 2 I

When the voltmeter is connected across the cell,

I==2 A

V1 = 12 – 2 (2) = 8 V

When the voltmeter is connected across the resistor,

V2 = IR

= 2 × 4 = 8 V

V1 = V2

Hence, from the above relation we can see that voltmeter placed across the cell and across the resistor, gives the same reading.

(b) Voltmeter has very high resistance to ensure that its connection does not alter the flow of current in the circuit. We connect it in parallel and we also know that current chooses only the low resistance path. Hence, it is connected in parallel to the load across which potential difference is to be measured.

Ammeter measures value of current flowing through the circuit so it should be connected in the series. Ammeter has very low resistance to ensure that all the current flows through it. Thus, it gives a correct reading of the current when connected in series.

• Q8

Define ionization energy.
How would the ionization energy change when electron in hydrogen atom is replaced by a particle of mass 200 times that of electron but having the same charge?

Marks:2

Ionization energy: The minimum amount of energy required to remove an electron from the outermost orbit of a neutral atom in its ground state is known as the ionization energy of that atom.

The ionization energy of Hydrogen atom is

EHme .....(1)

When mass of electron is replaced by a particle having mass = 200me, then

EH' 200me .....(2)

From (1) and (2), we have

EH' = 200EH = 200 × (−13.6) (EH=−13.6 eV)

= −2720 eV

• Q9

Calculate the shortest wavelength of the spectral lines emitted in Balmer series.

[Given Rydberg constant, R = 107 m–1]

Marks:2

• Q10

Define modulation index. Why is it kept low? What is the role of a bandpass filter?

Marks:2