PRE Board Exam class X11                  

  Time Allowed 1.5Hr.           Subject-physics                    M.M.-50

All Questions are compulsory.

 

Q1: What does q1 +q2 signify in electrostatics?1

Q2: Can electrostatics potential at a point be zero, while electric field at that point is not zero?1

Q3: A carbon resistor of 47 k ohm is to be marked with rings of different colours for identification. Write the sequence of the colours.1

Q4: How will the magnetic field intensity at the centre of a circular coil carrying current change, if the current through the coil is doubled and radius of the coil is halved.1

Q5: Why do magnetic lines of force prefer to pass through ferromagnetic substance than through air?1

Q6: A wire of certain radius is stretched so that its radius decreased by a factor of n. calculate its new resistance.2

Q7: Alloys of metals have greater resistivity than their constituent metals why.2

Q8: A charge q is placed at the centre of the line joining two equal charges Q. show that the system of three charges will be in equilibrium if q = -Q/4.2

Q9: Two identical short magnet a and B of magnetic moments m each are placed at a distance d with their axes perpendicular to each other. Find the magnetic field at a point p mid way between the two dipoles.2

Q10: The maximum torque acting on  a coil of effective area 0.04 m² is 4 * 10^-8 Nm when the current in it is 100 uA. Find the magnetic induction in which it is kept.2

Q11: Derive the condition for obtaining maximum current through the external resistance connected across a mixed grouping of cells.2

Q12: Deduce an expression for the capacitance of  a parallel plate capacitor when a dielectic slab is inserted between its plate.2

Q13: Apply Biot – Savart law to find the magnetic field due to a circular current carrying loop at  a point on the axis of the loop. 2

Q14: Discuss refraction at convex spherical surface when object in rarer medium and image formed is real.2

Q15: How is n-type semiconductor formed? Deduce an expression for the conductivity of a n-type semiconductor.3

Q16: A battery of emf V and internal resistnace r sends currents I₁ and I₂ , when connected to external resistance  R₁ and R₂ respectively. Find the emf and internal resistance of the battery.3

Q17: Prove that in an RL circuit, the voltage leads the current by π/2. 3

Q18: An infinite plane sheet of charge density 10 C m is held in air. In this situation how far apart are two equipotential surfaces, whose p.d. is 5V?3

Q19: Drive an expression for the mutual inductance of two long solenoids. State the factors on which mutual inductance depend. 3

Q20: What is meant by rms value of an alternating current? Derive a relation between it and its peak value.3

Q21: With the help of a labeled diagram, explain the principle, construction and working of an ac generator. Derive the expression for the induced emf and current.3

Q22: Apply Gauss’s theorem to show that for a spherical shell, the electric field inside the shell vanishes, whereas outside it, the field is as if all the charge had been concentrated at the centre.3

Q23: Discuss Common base amplifier with input and output phase relationship.3