Science (English Medium) इयत्ता १२ - CBSE Question Bank Solutions for Physics

A device X is connected across an ac source of voltage V = V₀ sin ωt. The current through X is given as 

`I = I_0 sin (omega t + pi/2 )`

1) Identify the device X and write the expression for its reactance.

2) Draw graphs showing the variation of voltage and current with time over one cycle of ac, for X.

3) How does the reactance of the device X vary with the frequency of the ac? Show this variation graphically.

4) Draw the phasor diagram for the device X.

Two metallic wires, P₁ and P₂ of the same material and same length but different cross-sectional areas, A₁ and A₂ are joined together and connected to a source of emf. Find the ratio of the drift velocities of free electrons in the two wires when they are connected (i) in series, and (ii) in parallel.

Give one example of use of eddy currents.

Use de-Broglie's hypothesis to write the relation for the n^th radius of Bohr orbit in terms of Bohr's quantization condition of orbital angular momentum ?

State the essential conditions for diffraction of light ?

Using Rydberg formula, calculate the longest wavelength belonging to Lyman and Balmer series. In which region of hydrogen spectrum do these transitions lie?
[Given R = 1.1 ✕ 10⁷ m⁻¹]

Answer the following question :
Define 'bandwidth' and describe briefly its importance in communicating signals ?

 How are eddy currents produced ?

Describe briefly three main useful application of eddy currents ?

A proton and an alpha particle are accelerated through the same potential. Which one of the two has (i) greater value of de−Broglie wavelength associated with it and (ii) less kinetic energy. Give reasons to justify your answer.

A deuteron and an alpha particle are accelerated with the same accelerating potential greater value of de-Broglie wavelength, associated it ?

Monochromatic light of frequency 5.0 × 10¹⁴ Hz is produced by a laser. The power emitted is 3.0 × 10^–3 W. Estimate the number of photons emitted per second on an average by the source ?

An electron is accelerated from rest through a potential V. Obtain the expression for the de-Broglie wavelength associated with it ?

Using Rydberg formula, calculate the wavelengths of the spectral lines of the first member of the Lyman series and of the Balmer series.

The given graph shows the variation of photo-electric current (I) versus applied voltage (V) for two difference photosensitive materials and for two different intensities of the incident radiations. Identify the pairs of curves that correspond to different materials but same intensity of incident radiation.

Block diagram of a receiver is shown in the figure:

(a) Identify ‘X’ and ‘Y’.

(b) Write their functions.

In a series LCR circuit connected to an ac source of variable frequency and voltage ν = v_m sin ωt, draw a plot showing the variation of current (I) with angular frequency (ω) for two different values of resistance R₁ and R₂ (R₁ > R₂). Write the condition under which the phenomenon of resonance occurs. For which value of the resistance out of the two curves, a sharper resonance is produced? Define Q-factor of the circuit and give its significance.

When monochromatic light travels from a rarer to a denser medium, explain the following, giving reasons:

(i) Is the frequency of reflected and refracted light same as the frequency of incident light?

(ii) Does the decrease in speed imply a reduction in the energy carried by light wave?

A wheel with 8 metallic spokes each 50 cm long is rotated with a speed of 120 rev/min in a plane normal to the horizontal component of the Earth’s magnetic field. The Earth’s magnetic field at the place is 0.4 G and the angle of dip is 60°. Calculate the emf induced between the axle and the rim of the wheel. How will the value of emf be affected if the number of spokes were increased?

Distinguish between ‘Analog and Digital signals’.