Science (English Medium) Class 12 - CBSE Question Bank Solutions for Physics

A device 'X' is connected to an ac source V = V₀ sin ωt. The variation of voltage, current and power in one cycle is shown in the following graph:

(a) Identify the device 'X'.
(b) Which of the curves A, B and C represent the voltage , current and the power consumed in the circuit? Justify your answer.
(c) How does its impedance vary with frequency of the ac source? Show graphically.
(d) Obtain an expression for the current in the circuit and its phase relation with ac voltage.

State Huygen’s principle.

Consider a plane wave front incident on a thin convex lens. Draw a proper diagram to show how the incident wave front traverses through the lens and after refraction focusses on the focal point of the lens, giving the shape of the emergent wave front.

Use Huygens' principle to verify the laws of refraction.

Define the distance of closest approach. An α-particle of kinetic energy 'K' is bombarded on a thin gold foil. The distance of the closest approach is 'r'. What will be the distance of closest approach for an α-particle of double the kinetic energy?

Write two important limitations of Rutherford's nuclear model of the atom.

How does one explain the emission of electrons from a photosensitive surface with the help of Einstein's photoelectric equation?

The work function of the following metals is given : Na 2.75 ev, K = 2.3 eV, Mo = 4.17 eV and Ni = 5.15 eV. Which of these metals will not cause photoelectric emission for radiation of wavelength 3300 Å from a laser source placed 1 m away from these metals? What happens if the laser source is brought nearer and placed 50 cm away?

Predict the polarity of the capacitor in the situation described below :

Name the electromagnetic radiations used for (a) water purification, and (b) eye surgery.

Why are infra-red waves often called heat waves? Explain.

What do you understand by the statement, "Electromagnetic waves transport momentum"?

Using Huygens’ principle, verify the laws of reflection at a plane surface.

An electron in an atom revolves round the nucleus in an orbit of radius r with frequency v. Write the expression for the magnetic moment of the electron.

Answer the following question.

Show that the density of the nucleus is independent of its mass number A.

Output characteristics of an n-p-n transistor in CE configuration is shown in the figure.

Determine:

(i) dynamic output resistance

(ii) dc current gain and

(iii) ac current gain at an operating point V_CE = 10 V, when I_B = 30 μA.

Using this principle draw a diagram to show how a plane wave front incident at the interface of the two media gets refracted when it propagates from a rarer to a denser medium. Hence verify Snell's law of refraction.

Use Huygens’s principle to explain the formation of diffraction pattern due to a single slit illuminated by a monochromatic source of light.

When the width of the slit is made double the original width, how would this affect the size and intensity of the central diffraction band?