(Model Paper) Download 12th Class Model Paper ( PHYSICS )

SECTION A

Long Answer Type Questions:
Q.1. State the Theorem which relates the enclosed charge inside a closed surface with surface integral of Electric filed. Use this theorem to obtain the electric field due to an  infinite plane sheet of charge.
OR
Show that capacity of a parallel plate capacitor depends upon the geometrical factors of capacitor. If the distance between the plates is increased how does it affect the capacitance and energy of the capacitor? (5 Marks)

Q.2. Two long straight parallel wires carry currents I1 and I2 in the same direction. Find an expression for the force per unit length between them. Depict the pattern of magnetic field lines. Use the expression to define S.I unit of current.
OR
Highly energetic positively charged particles are usually used to carry nuclear reactions. Give name, principle, construction and working of the machine used for the
purpose. (5 Marks)

Q.3. If an a.c. of the form I=I0 sinώt is fed to an LCR series circuit so that emf leads the current by . Deduce an expression for average power consumed. Hence define power factor.
OR
Name the device which converts mechanical energy into alternating electrical energy. Give its principle, construction and theory with the help of diagram. (5 Marks)

Q.4. Derive lens markers formula in case of double convex lens. Write down the sign conventions and assumption used.
OR
With the help of a ray diagram, illustrate the formation of the final image of an object in the compound microscope. Derive the expression for magnifying power. How it can be increased? (5 Marks)
 

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