PHYSICS By MAMTA SINGH

Q1-State two main considerations taken into account while choosing the objective of astronomical telescope.   (2) Q2-State the advantages of reflecting type telescope over the refracting type.  (2) Q3-Draw the ray diagram of compound microscope and write the expression for its magnifying power at normal adjustment.   (2) Q4-Draw the ray diagram  to show use of TIR in (I) optical fibre (ii)a prism that bends the ray by 90⁰.   (2) Q5-Derive the lens makers formula. Write the assumptions used in it.  (3) Q6-Prove the lens formula using concave formula and also it's magnification.  (3) Q7-A biconvex lens has a focal length 2/3 times the radius of curvature of either surface.Calculate the refractive index of lens material.     (  2) Q8-Light from a point source in air falls on a convex spherical glass surface of refractive index 1.5 and radius of curvature 20 cm.The distance of light source from the glass surface is 100 cm.At what position is the image formed?   (2)  Q9-Deri

A Faraday Cage is a closed chamber consisting of a conducting material or a mesh of a conducting material. A Faraday cage or Faraday shield is an enclosure made of a conducting matreial. The fields within a conductor cancel out with any external fields ,so the electric field within the conductor(enclosure) is zero. Faraday cage was first invented by Michael Faraday in 1836 and it can block external static and non-static electric fields. These Faraday cages act as big hollow conductors ,one can put things in to shield them from electrical fields .Any electrical shocks the cage receives , pass harmlessly around the outside the cage. When an external electric field operates on a Faraday cage,the charges within the cage rearrange themselves to direct counteract the field and thus shield the interior of the cage from the external field. The action of a Faraday cage may depend on whether or not it is grounded. Faraday cage can block the effects

PHYSICS SAMPLE PAPER(1)-2020  CLASS 12TH  PHYSICS TIME 3:00Hrs            MAXIMUM  MARKS  70 General Instructions: (1) All questions are compulsory. There are 33 questions in all.  (2) This question paper has five sections: Section A, Section B, Section C, Section D and Section E. (3) Section A contains ten very short answer questions and four assertion reasoning MCQs of 1 mark each; Section B has two case based questions of 4 marks each    (4)Section C contains nine short answer questions of 2 marks each, Section D contains five short answer questions of 3 marks each and Section E contains three long answer questions of 5 marks each.                                                   SECTION A Q1 Write the SI unit of gyromagnetic ratio. Q2 What is the electric potential due to an electric dipole at an equatorial point? Q3 What is the value of angular momentum of electron in the second orbit of Bohr’s model of hydrogen atom? Q4 Which semiconductors are preferred to make LED&

Electromagnetic waves are transverse in nature.Electromagnetic waves consist of an electric vector (E)  and a magnetic vector (B) mutually perpendicular to each other and they are also perpendicular to the direction of propagation of the wave. The electric vector (E) ,magnetic vector (B) and the propagation vector (K) form a right handed set (all the three mutually perpendicular to each other).

In case of reverse biasing when the reverse bias voltage is made sufficient high,the electric field across the depletion region increased.            V=Ed The high electric field across the juction applies force on the minority charge carriers in the n-side and in the p-side. When the energetic free electrons collide with the atoms of the crystal in the charge depletion region,then the covalent bond breaks and electron-hole pairs are produced. These free electrons further help in creating more electron- hole pairs by participating in the collision process with the other atoms of the crystal creating large number of electron-hole pairs. This process is known as avalanche breakdown

IMPORTANT TOPIC FOR CLASS12TH PHYSICS CBSE BOARD EXAMINATION: Subject :  PHYSICS    By- Mamta Singh  Ch.-1 Electric flux Force and Torque on the electric dipole. Electric field on the axial and equatorial line.  Statement of Gauss-Theorem. Applications of Gauss- Theorem,all three applications of Gauss theorem especially charged spherical shell. Ch.-2 Capacitance and factor’s affecting capacitance.  Energy stored in a capacitor and its energy density( formula only). Capacitance of a parallel plate capacitor with a dielectric slab placed in between. (IMPORTANT) DRAW EQUIPOTENTIAL SURFACE TO A POINT CHARGE,LINE CHARGE,PLANE ELECTRIC FIELD AND DUE TO A ELECTRIC DIPOLE. Equi-potential surface and its properties. Relation between electric field and electric potential.  Effect on various parameters when a dielectric slab is introduced b/w the plates of parallel plate capacitor. Principe of parallel plate capacitor. Potential at any general point of electric dipole. Ch.3 (7 marks)

It is a device which make use of accelerated electron beams to study very minute/small objects like viruses,microbes etc.It is used for obtaining high resoution images of biological and non - biological specimens. It has the magnification of the order of 10⁵. It uses a beam of accelerated electrons as a source of illumination and it is having extremely high resoution. Electrons /electron beam have much shorter wavelength than the visible light which is used in other microscope.The resolving power of a microscope is inversely proportional to the wavelength of light used.Hence electron microscope is having high resolution.