CBSE Physics Previous Question Paper 
All India (Comptt.) 1998 (Part - 9)

Q. 1. Name the physical quantity whose SI unit is Coulomb/Volt.

Q. 2. Write the frequency limit of visible range of electromagnetic spectrum in kHz.

 

Q. 3. How does the conductance of a semi-conducting material change with rise in temperature?

Q. 4. The force F experienced by a particle of charge e moving with velocity v in a magnetic field B is given by Of these, name the pairs of vectors which are always at right angles to each other.

 

Q. 5. Two wires A and B are of same metal, have the same area of cross-section and have their lengths in the ratio 21. What will be the ratio of currents flowing through them respectively when the same potential difference is applied across length of each of them?

 

Q. 6. Calculate the rms value of the alternating current shown in the figure.

 

Q. 7. The image of an object formed by a lens on the screen is not in sharp focus. Suggest a method to get clear focusing of the image on the screen without disturbing the position of the object, the lens or the screen.

 

Q. 8. Two protons A and B are placed between two parallel plates having a potential difference V as shown in the figure. Will these protons experience equal or unequal force?

Q. 9. Define the terms ‘threshold frequency’ and ’stopping potential’ for photo-electric effect. Show graphically how the stopping potential, for a given metal, varies with frequency of the incident radiations. Mark threshold frequency on this graph.

 

Q. 10. Draw labelled diagram of a Leclanche cell. Write the function of charcoal powder and manganese dioxide used in its porous pot.

 

Q. 11. How does the mutual inductance of a pair of coils change when
(i) the distance between the coils is increased ?
(ii) the number of turns in each coil is decreased ?
Justify your  in each case.

 

Q. 12. Define the terms magnetic inclination and horizontal com¬ponent of Earth’s magnetic field at a place. Establish the relationship between the two with the help of a diagram.

 

Q. 13. An electron in an atom revolves around the nucleus in an orbit of radius 0.53 A. Calculate the equivalent magnetic moment if the frequen¬cy of revolution of electron is 6.8 x 10⁹ MHz.

 

Q. 14. Write the function of base region of a transistor. Why is this region made thin and slightly doped?

 

Q. 15. Derive an expression for the energy stored in a charged parallel plate capacitor with air as the medium between its plates.

 

Q. 16. In the diagram given below for the stationary orbits of the hydrogen atom, mark the transitions representing the Balmer and Lyman series.

 

Q. 17. The given figure shows an inductor L and resistor R connected in parallel to a battery B through a switch S. The resistance of R is the same as that of the coil that makes L. Two identical bulbs, P and Q are put in each arm of the circuit as shown.

When S is closed, which of the two bulbs will light up earlier? Justify your .

Q. 18. Two point electric charges of values q and Iq are kept at a distance d apart from each other in air. A third charge Q is to be kept along the same line in such a way that the net force acting on q and 2q is zero. Calculate the position of charge Q in terms of q and d.

 

Q. 19. Explain, with the help of a circuit diagram, the use of potentiometer for determination of internal resistance of a primary cell. Derive the necessary mathematical expression.

Q. 20. (i) Sketch the wave-fronts corresponding to converging rays. (ii) Verify Snell’s law of refraction using Huygens’ wave theory.

Q. 21. An electric dipole is held in a uniform electric field. (i) Show that no translator}’ force acts on it
(ii) Derive an expression for the torque acting on it

 

Q. 22. Derive an expression for the width of the central maxima for diffraction of light at a single slit. How does this width change with increase in width of the slit?

 

Q. 23. A capacitor of capacitance 100 μF and a coil of resistance 50Ω and inductance 0.5 H are connected in series with a 110V, 50 Hz source. Calculate the rms value of the current in the circuit.

 

Q. 24. Draw a labelled ray diagram to show the image formation in a reflecting type telescope. Write its two advantages over a refracting type telescope. On what factors does its resolving power depend?

 

Q. 25. Define the terms ’solar constant’ and ’solar luminosity’. Explain how their knowledge helps us to calculate the surface temperature of the sun. Derive the necessary mathematical expression.

Q. 26. An object is kept in front of a concave mirror of focal length 15 cm. The image formed is three times the size of the object. Calculate two possible distances of the object from the mirror.

Q. 27. A voltmeter V of resistance 400 Ω is used to measure the potential difference across a 100 Ω. resistor in the circuit shown here.
(a) What will be the reading on the voltmeter?
(b) Calculate the potential difference across 100 Ω resistor before the voltmeter is connected.

 

Q. 28. Derive a mathematical expression for the force per unit length acting on each of the two straight parallel metallic conductors carrying current in the same direction and kept near each other. Why do such current carrying conductors attract each other?

 

Or

 

Derive a mathematical expression for the force acting on a current carrying straight conductor kept in a magnetic field. State the rule used to determine the direction of this force.

 

 

Q. 29. (i) Draw a labelled diagram of Thomson’s experimental set-up to determine e/m of electrons, (ii) Explain, by deriving the necessary mathematical expression, how e/m of electrons can be determined by this method.

 

Q. 30. Define the terms ‘potential barrier’ and ‘depiction region’ for a p-n junction. Explain, with the help of a circuit diagram, the use of a p-n diode as a full wave rectifier. Draw the input and output wave-forms.