CBSE Delhi-Set-3-2016
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Q1
Define’ quality factor’ of resonance in series LCR circuit. What is its SI unit?
Marks:1View AnswerAnswer:
The Q factor of series resonance circuit is defined as the ratio of the voltage developed across the inductor or capacitor at resonance to the impressed voltage, which is the voltage across R
It is dimensionless hence, it has no units. -
Q2
A point charge +Q is placed at point O as shown in the figure. Is the potential difference VA – VB positive, negative or zero?
Marks:1View AnswerAnswer:
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Q3
How does the electric flux due to a point charge enclosed by a spherical Gaussian surface get affected when its radius is increased?
Marks:1View AnswerAnswer:
According to Gauss’s law, flux through a closed surface is given by
Where q is the charge enclosed by the Gaussian surface.
Since, on increasing the radius of the Gaussian surface, charge, q remains unchanged, so the flux through the spherical Gaussian surface will not be affected when its radius is increased.
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Q4
Why are microwaves considered suitable for radar systems used in aircraft navigation?
Marks:1View AnswerAnswer:
Microwaves are considered suitable for radar system used in aircraft navigation because they have a short wavelength range from 10-3 m to 0.3m, which makes them suitable for long distance communication.
Another reason for using microwaves is that they can penetrate through clouds also.
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Q5
Write the underlying principle of a moving coil galvanometer.
Marks:1View AnswerAnswer:
When a current-carrying coil is placed in a magnetic field, it experiences a torque. This is the underlying principle of a moving coil galvanometer.
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Q6
State Brewster’s law.
The value of Brewster angle for a transparent medium is different for light of different colours. Give reason.Marks:2View AnswerAnswer:
Brewster law : The law states that the tangent of the polarising angle of incidence of a transparent medium is equal to its refractive index.
μ = tan ip
The refractive index of a material depends on the color or wavelength of light. As the polarizing angle depends on refractive index (μ = tan ip), so it also depends on wavelength of light.
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Q7
Explain the terms (i) Attenuation and (ii) Demodulation used in Communication System.
Marks:2View AnswerAnswer:
(i) Attenuation: The loss of strength of a signal while propagating through a medium.
(ii) Demodulation: The process of retrieval of information from the carrier wave at the receiver end. This is the reverse process of modulation.
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Q8
Plot a graph showing variation of de-Broglie wavelength , where V is accelerating potential for two particles A and B carrying same charge but of masses m1, m2 (m1> m2). Which one of the two represents a particle of smaller mass and why?
Marks:2View AnswerAnswer:
The slope of the smaller mass is larger, therefore, plot A in the above graph is for mass m2. -
Q9
Two cells of emfs 1.5 V and 2.0 V having internal resistances 0.2 Ω and 0.3 Ω respectively are connected in parallel. Calculate the emf and internal resistance of the equivalent cell.
Marks:2View AnswerAnswer:
Given,
E1 = 1.5 V
E2 = 2 V
r1 = 0.2 Ω
r2 = 0.3 Ω
Effective EMF of two cells connected in parallel can be calculated as:
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Q10
A nucleus with mass number A = 240 and BE/A = 7.6 MeV breaks into tow fragments each of A = 120 with BE/A = 8.5 MeV. Calculate the released energy.
Marks:2View AnswerAnswer:
The binding energy of the nucleus of mass number 240 is, B1 = 7.6 x 240 = 1824 MeV
The binding energy of each product nucleus is, B2 = 8.5 x 120 = 1020 MeV
The energy released as the nucleus breaks is
E = 2B2 – B1 = 2 x 1020 – 1824 = 216 MeV
Alternatively: Gain in binding energy for nucleon is about 0.9 MeV.
Hence, the total gain in binding energy
DE = 240 × 0.9
DE = 216 MeV.
