Mongar Higher Secondary School

Mongar Higher Secondary School Monger Bhutan Mid – Term Examination – 2010

Class: 12. Time: 3hrs Subject: Physics. Marks: 100

Part – I (40 marks) Answer all the question in this part I choose the correct. (10x1 = 10) 1. Which of the following is the unit of electric intensity? a) NM b) NC c) NC – 1 d) NS – 1 2. A soap bubble is given a negative charge. Then its radius a) Decreases b) increases c) no change d) nothing can be predicted. 3. A surface is hold perpendicular to the direction of lines of force of electric field. Electric flux linked with it is a) Zero b) infinite c) minimum d) maximum 4. Look at the diagram

The net capacitance

a) ∑OA b) 2∑OA c) 3∑O A d) 4∑OA d d d d 5. A resistor has Blue, Red, orange and silver bands its value may be a) 62000 ±10% b) 6200 ± 5% c) 6200 ± 10% d) 62000 ± 5% 6. The emf of the leclanche cell is a) 1.5 volt b) l.08v c) 1.2v d) 2v 7. Two electric lamps of 40watt each are connected in parallel. The power consumed by the combination will be a) 20 watt b) 80 watt c) 40 watt d) 160 watt 8. Flux density B is related to the magnetic flux by the relation  B a) B= B b) Ф = c) A = Bx Ф d) B2 = Ф A A B A B B

1 9. A Choke coil is used as a resistor in a) Potentiometer circuit b) d.c.circuit c) a.c circuit d) wheat stone circuit. 10.A transformer steps up or steps down only a) a.c b) d.c) c) either a.c or d.c d) a.c mixed with dc

Question II Write True of False. (5 mark) 1) A capacitor is an arrangement to provide large capacity in smaller space. 2) A meter Bridge is a modified form of wheat stone bridge. 3) Primary cells can be reused by recharging. 4) Lenz’s law is in accordance with law of conservation of energy. 5) A Generator is converting electrical energy into kinetic energy.

Question III. Fill in the blanks with suitable answer.[5 marks] 1) Relative permittivity of medium is defined as……………………… ∑ ∑o ∑o ∑

2) Di electric constant of a good conductor is ………….. (infinite / zero) 3) We prefer to use a wire made up of (pure metal/ alloy) in a potentiometer. 4) Pure water is a ………..(conductor/ non – conductor) 5) In case of electrical resonance the current in the circuit is………. (maximum/minimum)

Question IV. Match the following [10 marks] Please take and write both left and right side on your paper with correct answer. Don’t write the numbers A B Magnetic moment Deflection magnetometer moving coil Galvanometer Suspension of a bar magnet Perpendicular to magnetizing field. Tangent law Motor rule Dia magnetic bar Bil sin θ Flemings right hand rule South to North Fleming left land rule Magnetic dipole A current carrying loop Tesla Magnetic field strength North – south direction Magnetic force weber/ m Magnetic torque Generator rule Bia cos θ Along magnetizing field.

2 Question V. Answer the following question.10x1=10

1) Find the dipole moment of an electric dipole of having charges - 5c and +10c separated by 10cm. 2) How can you transfer whole of the charge from one conductor to another? 3) State Gauss theorem of electro static. 4) The capacity of a storage cell is 20Ah. What in the maximum current that can be drawn from it in ½ an hour. 5) What is volta effect? 6) What is curie law? 7) Write the vector form of Biot’s savert law? What does it tell about? 8) Define Reduction factor of a Galvanometer? 9) If the No. of turns in primary of a transformer is 200 turns and the I/P is 50v. The no. of turns in secondary is 200; then what could be the O/P voltage. Is it a step up transformer? 10) Differentiate with any two points about the motion of a charged particle in electric and magnetic field.

PART II SECTION A (3x8=24) Answer any 3 out of 4 questions. The intended marks is given against the questions Question VI 1) a) In hydrogen atom the electrical force of attraction between electron and proton is 8.1 x 10 – 8N.Calculate the distance between the electron and proton. Take e=1.6 x 10 – 19c [3] b) Obtain the expression for the energy of an electric dipole in an uniform Electric field. [3] c) A metallic ball carrying the charge of 10c is fixed at a distance of ‘d’ in front of an infinite metal plate. Trace the line of force meeting the plate. (2)

2) a) A charge of nine nano coulomb is present inside the cube. Calculate i) flux linked with the cube. ii) Flux linked with the one of the faces of cube. (3)

3 b) Draw the relationship between temperature and Resistivity. From there define what is critical temperature. Also name two superconductors with its respective critical temperature. [3] c) Find the potential at a point due to a +ve charge of 100 X 10-6 C at a distance of 9m. [2] 3) a) Two resistors of 3Ω and 2Ω are in parallel connection and a potential difference of 12v is applied across them. Find. i) the equivalent resistance ii) the circuit current iii) the branch current. [3] b) Draw neatly the diagram of a potentiometer and state its principle. Also draw the relationship between V and L. [3] c) Find the un known resistance x connected in the circuit. Assume that the current through the galvanometer is zero. [2]

4) a) Find the capacity of a parallel plate capacitor consisting of two plates, each of size 10cmx10cm, separated by 1mm thick mica plate of dielectric 6. [3] b) State the principle of a capacitor. What would happen if the distance in between the plates increases and area of the plates increases? [3] c) Calculate the no.if lines of forces coming out from a +v charge of 1c. [2] SECTION B(3x6=18) Answer any 3 questions out of 4 . Question VII. 1) a) Discuss the defects of simple voltaic cell and suggest the way to solve it. [3] b) Figure shows thermo emf E and Temperature T. of hot junction and the cold junction is maintained at O0c. Super imposing on the same curve, draw E- T.curve if the temperature of cold junction is raised to 1000c (3)

0 OC Tn Ti= 54 c 4 2) a) A house is fitted with a motor of 746watt 5 bulbs consuming 2A each and two fans of 80w each. If all the appliances are used for 5 hours a day calculate the monthly bill. Energy costs Nu.1 per unit. The energy is supplied at 220v. [3] b) Define and differentiate peltier’s effect and joule’s effect [3] 3) a) Obtain the expression of forces on a magnetic needle suspended in a uniform magnetic field of strength B. Also define magnetic moment and its direction.[3] b) A bar magnet when placed in the end on position producers a deflection of 450 in magnetometer. Another magnet when placed in end on position at the same place produces a deflection of 300. Compare the magnetic moments of two magnets. [3] 4) a) A Conductor with a cross section area of 1x10 – 4m2 carries an electric current of 1.2A. If the number electrons be 5x10 28m – 3, calculate the drift velocity. [3] b) Compare magnetic induction B, permeability μ, intensity of magnetization I, susceptibility K, temperature dependence and direction of magnetization with respect to Dia, fera and Ferro magnetic substances. [3]

SECTION C (3x6=18) Answer any 3 questions out of 4 Question VIII 1) a) An infinitively ling straight wire is bent into the shape as shown in fig. calculate the magnetic induction B at the centre O of the coil. [2]

2) Obtain the expression for magnetic induction B at any point inside the solenoid. [2] c) An ac current has the equation 50 sin 200t and its frequency is 500 Hz.an of 5 H capacitor of 5 micro fared connected with the source. calculate the max.E.M.F and max.current and the capacitive reactance in the circuit. [2]

3) a) State the conditions under which the magnetic flux linked with a circuit is +ve, - ve and zero. [2] b) A circuit has an inductance of 1 Henry and a resistance of 2000Ω. A 50 cycle A.C in applied to it. Calculate the reactance and impedance offered by the circuit. [2] c) Draw Growth and decay curve for an R.L. circuit. Also define what is time constant and write its unit. [2] 5 4) a) Discuss about the various sources loss of energy in case of a transformer. [2] b) i) Can electrolysis proceed with the help of ac current? ii) What is the value of power factor in the a.c circuit at resonance? iii) What is the nature of impendence of a R.L.C circuit at resonance? [2] c) i) A copper ring is suspended by means a thread such that its plane is vertical. A bar magnet approaches the centre of ring from right side what will happen to be ring. [1] ii) Fill in the blank. Eddy currents play a role analogous to that played by friction in machines. There we minimize friction by ……………..and here we minimize loss of energy by ………..the core. [1]

Physical constants

1. 1 = 9x10-9 SI Units 4Л∑o 2. – 27 Mass of proton Mp = 1.67 x 10 kg 3. – 1 – 31 Mass of e me = 9.1 x 10 kg 4. Charge on e -1 C - = 1.6x10– 19c 5. Charge on proton e + = 1.6x 10– 19c 6. – 12 ∑o = 8.854 x 10 SL units 7. Л radian = 1800 8. H = 0. 32 x 10 – 4 Tesla 9. – 7 μo = 4 x 10 SL unit 10. – 7 μo = 10 SL unit. 4Л