Osm Physics by Ashish

Zone Plate | Fresnel Diffraction Diffraction – Fresnel's Class Topic: Construction, Theory, Multiple Foci and Comparison with a Convex Lens A zone plate is a diffractive optical device consisting of a series of alternate transparent and opaque concentric circular rings. It works on the principle of Fresnel diffraction and the division of a wavefront into half-period zones. A zone plate focuses light by diffraction and interference rather than by refraction. It is an important application of Fresnel's half-period zone theory. It demonstrates how the superposition of secondary wavelets from alternate half-period zones can produce constructive interference at certain points on the axis. A zone plate behaves like a converging lens, although its focusing mechanism is entirely different from that of a conventional convex lens. Construction of a Zone Plate A zone plate is constructed by drawing a large number of concentric circles on a plane surf...

According to Huygens' principle, every point on a wavefront acts as a source of secondary wavelets. These secondary wavelets spread in all directions and interfere with one another. Fresnel assumed that the resultant intensity at any observation point can be calculated by considering the interference of secondary wavelets originating from different portions of the wavefront. To simplify this calculation, Fresnel divided the wavefront into a number of concentric annular regions called Fresnel's half-period zones . Geometrical Arrangement Consider a plane monochromatic wavefront ABCD travelling from left to right. Let P be an observation point situated at a distance from the wavefront. Draw a perpendicular PO from P to the wavefront such that: PO = b The point O is called the pole of the wavefront corresponding to the observation point P. With P as the centre, imagine a series of concentric spheres having radii: b + λ/2,   b + 2λ...

Definition: The phenomenon in which light waves bend around the edges of an obstacle or spread after passing through a narrow aperture and enter the geometrical shadow region is called diffraction of light. Dependence of Diffraction on Wavelength and Obstacle Size The extent of diffraction depends mainly on the wavelength of the wave and the dimensions of the obstacle or aperture. When the size of the obstacle or aperture is comparable to the wavelength, diffraction is considerable. When the size of the obstacle is much greater than the wavelength, diffraction is generally less pronounced. When the wavelength is large compared with the obstacle dimensions, the wave spreads considerably around the obstacle. Types of Diffraction Depending on the relative positions of the source, diffracting aperture or obstacle, and observation point, diffraction is broadly classified into two types: (I) Fresnel Diffraction (Near-Field Diffraction) (II) ...

Clausius–Clapeyron Equation | Physics Notes Derivation and physical significance of the phase-equilibrium relation The phase-equilibrium curve shown in a pressure–temperature (P–T) diagram can be described mathematically by a differential equation known as the Clausius–Clapeyron equation . It gives the relationship between pressure and temperature during a phase transition, such as melting, vaporisation or sublimation. 1. Derivation of the Clausius–Clapeyron Equation Consider two points B and C lying very close to each other on a phase-equilibrium curve. At point B, the temperature and pressure are T and p , respectively. At point C, the temperature and pressure are T + dT and p + dp , respectively. Since the two phases are in thermodynamic equilibrium at point B, their Gibbs free energies per molecule are equal: g 1 (T, p) = g 2 (T, p) (1) Similarly, at point C: g 1 (T + dT, p + dp) = g 2 (T + dT, p + dp) For small changes in temperature and ...

Elastic Properties of Matter | Physics Notes Elastic Properties of Matter 17. Bending of Beams and Structural Applications When a beam is supported at its two ends and loaded at the middle, it bends under the action of the applied load. During bending, the longitudinal layers of the beam undergo extension or compression. For a simply supported beam subjected to a downward central load, the upper layers are compressed, whereas the lower layers are stretched. Between these two regions lies a neutral surface , where the longitudinal strain and bending stress are zero. According to the theory of simple bending, the magnitude of longitudinal bending stress at a distance \(y\) from the neutral axis is \[ \boxed{\sigma_b=\frac{M_b y}{I_A}} \] where \(\sigma_b\) = longitudinal bending stress, \(M_b\) = bending moment at the section, \(y\) = perpendicular distance from the neutral axis, \(I_A\) = second moment of area of the cross-section about the neutral...

Elastic Constants by Searle's Dynamical Method 1. Aim To determine Young's modulus \(Y\), modulus of rigidity \(n\), and Poisson's ratio \(\sigma\) of the material of a given wire by Searle's dynamical method using the time periods of oscillation. 2. Apparatus Required Searle's dynamical apparatus, two identical cylindrical bars, experimental wire, rigid supporting stand, stopwatch, screw gauge, vernier calipers, metre scale and physical balance. 3. Theory When an elastic body is deformed within its elastic limit, restoring forces or couples are developed. These restoring actions tend to bring the body back to its original configuration. Searle's dynamical method determines the elastic constants of a wire by observing two independent modes of oscillation of an arrangement containing the wire and two identical bars. The first mode is associated with flexural deformation, while the second mode involves torsional deformation. Th...

Experiment: Non-Uniform Bending of a Beam Study of Bending of a Beam and Determination of Young's Modulus Method: Non-Uniform Bending (Central Loading Method) 1. Aim To study the non-uniform bending of a rectangular beam supported on two knife edges and to determine Young's modulus of the material by applying a load at the centre of the beam. 2. Apparatus Required Rectangular beam (metallic or wooden), two knife-edge supports, weight hanger, slotted weights, travelling microscope, metre scale, Vernier calipers and screw gauge. 3. Theory When a rectangular beam is supported horizontally on two knife edges and a load is applied at its midpoint, the beam bends downward. The bending moment varies along the length of the beam; therefore, this type of bending is called non-uniform bending . For a simply supported beam carrying a central load, the depression at the midpoint is given by \[ y=\frac{Wl^3}{48YI} ...