Sample Paper – 2009

Class – XII

Subject – Physics

Based on the new pattern for CBSE board examination 2009

## Time allowed : 3 hours Maximum Marks : 70

*General Instructions :*

*(i) **All questions are compulsory.*

*(ii) **This paper includes questions from chapters one to eight only*

*(iii) **Question numbers 1 to 8 are very short answer type questions, carrying one mark each.*

*(iv) **Question numbers 9 to 18 are short answer type questions , carrying two marks each.*

*(v) **Question numbers 19 to 27 are also short answer type questions, carrying three marks each.*

*(vi) **Question numbers 28 to 30 are long answer type questions, carrying five marks each.*

*(vii) **Use of calculators is not permitted. However, you may use log tables, if necessary.*

Q.1> Name two electromagnetic waves that are emitted by an incandescent bulb.

Q.2 > Name the physical quantity whose SI unit is (a) Coulomb per Volt (b) Volt meter

Q.3> A student obtains resistances of 3, 4, 12 and 16 ohms using only two metallic resistance wires either separately or joined together. What is the value of resistance of each of these wires.

Q.4> Mention one advantage and one disadvantage of AC over DC

Q.5> In a certain arrangement a proton does not get deflected while passing through a magnetic field region. Under what conditions is it possible?

Q.6> Lorentz force is given by F = Q ( VxB ). Of these, name the pairs of vectors which are always at right angles to each other.

Q.7> Mention 2 properties of alloys from which permanent magnets are made

Q.8> An alpha particle and a proton are accelerated by the same potential difference. Calculate the ratio of linear momenta acquired by the two.

Q.9> Define “Intensity of Electric field” at a point. At what points is the electric dipole field intensity parallel to the line joining the charges?

Q.10> Capacitor P, Q and R each have a capacitance C. A battery can charge the capacitor P to a potential V. If after charging P, the battery is disconnected from it and the charged capacitor P is connected in following separate instances to Q and R

(a) In parallel to Q and

(b) In series to R,

Then, what will be the potential difference across P?

Q.11> An inductor of 2mH carries a current of 5A. The direction of current is reversed in it in half a second due to which a voltage is produced across the inductor. What is this phenomenon known as? Find the voltage produced.

Q.12> Why is conductivity of electrolytes less than that of metals?

Q.13> A matrix of N x M cells each of emf E and internal resistance r is connected to an external resistor R. Write an expression for the current flowing in R. Under what condition will this current be maximum.

Q.14> “N” identical cells each of emf E and internal resistance r are connected in series to an external resistor R. Find the internal resistance r in terms of the current I flowing in the circuit.

(c) How does the internal resistance very with temp?

Q.15> A metal wire is stretched to increase its length by 10%. What is the percentage change in its resistance? Will the resistivity of the wire change?

Q.16> Plot a graph to show how the following quantities vary with the frequency of the source. (a) Resistance (b) Capacitive reactance (c) Inductive reactance

Q.17> 2 protons A and B are placed in the space b/w a parallel plate capacitor. “A” is placed closer to the left plate while “B” is placed exactly in the center. Which of them will experience a greater force? Give reasons.

Q.18> An armature coil consists of 20 turns of wire, each of area A = 0.09m^{2} and total resistance 15.0 . It rotates in a magnetic field of 0.5T at a constant frequency of 150/π Hz. Calculate the value of (i) maximum (ii) average induced emf produced in the coil

Q.19** >** Two point charges Q and 2Q at kept D distance apart. A third charge X is to be kept on the line joining them in such a way that the net force on Q and 2Q is zero. Calculate the position of X in terms of Q and D

Q.20> A 100ohm Resistor and a 200ohm resistor are connected in series across an 84 volt cell. The potential difference across 100ohm is found using a 400ohm Voltmeter. What will be the voltmeter reading. What will be the potential difference across 100ohm if measured with a potentiometer.

Q.21> What are the 3 magnetic elements of Earth.

(b) At a place the vertical and horizontal components of earth’s magnetic field are equal to 20G each. What is the net magnetic field and the angle of dip at this place?

Q.22> A wire of uniform cross section and length L has a resistance of 16ohm. It is cut into four equal parts. Each part is stretched uniformly to length L and all the four stretched parts are connected in parallel. Calculate the total resistance of the combination so formed.

Q.23> Write any four characteristics of EM waves. Give 2 uses of (a) Micro waves (b) X rays.

Q.24> State Gauss theorem. Using it derive the Electric field intensity due to a plane sheet of charge.

Q.25> Why is a potentiometer preferred over a voltmeter to measure the emf of a cell? How can a potentiometer be made more sensitive?

Q.26> Derive the force b/w 2 infinite long parallel straight wires carrying current in the same direction. Hence define one ampere.

Q.27> A potential difference V is applied across a conductor of length L and diameter D. How are the electric field and the resistance R of the conductor affected when in turn

(a) V is halved (b) L is halved (c) D is doubled

Q.28> State Biot-Savart Law. Use it to obtain the magnetic field at an axial point distanced z from the center of a circular coil of radius ‘a’, carrying a current I. Hence compare the magnitudes of the magnetic field of this coil at its center and at an axial point for which z = √3 a.

Q.29> When an inductor L and a resistance R in series are connected across a 12 V , 50Hz ac source, a current of 0.5A flows in the circuit. The current differs in phase from applied voltage by π/3 radian. Calculate the value of R.

(b) A capacitor and a bulb are connected in series to an ac source. Explain, how the brightness of the bulb will change when

(a) Distance b/w the plates of the capacitor is increased

(b) A dielectric slab is introduced in the capacitor

Q.30> A parallel plate capacitor of plate area A and separation d is charged to a potential V. The battery is then disconnected and a dielectric slab of thickness d and dielectric constant K is inserted in the capacitor. What change, if any, will take place in

(a) Charge on the plates (d) Voltage across the capacitor

(b) Electric field b/w the plates (e) Capacitance of the capacitor

(c) Energy stored