Physics 2006 Set 1 Close

Subjective Test

(i)All questions are compulsory.(ii) There are 30 questions in total. Questions 1 to 8 carry one mark each, Questions 9 to 18 carry two marks each, Question 19 to 27 carry three marks each and Question 28 to 30 carry five marks each.(iii)There is no overall choice. However, an internal choice has been provided.(iv)Wherever necessary, the diagrams drawn should be neat and properly labelled.(v) Use of calculators is not permitted. Question 1 ( 1.0 marks) Define the term dielectric constant of a medium in terms of capacitance of a capacitor.Question 2 ( 1.0 marks) Sketch a graph showing variation of resistivity of carbon with temperature.Question 3 ( 1.0 marks) The vertical component of Earths magnetic field at a place is times the horizontal component. What is the value of angle of dip at this place?Question 4 ( 1.0 marks) With what purpose was famous DavissonGermer experiment with electrons performed?Question 5 ( 1.0 marks) Name the type of communication in which the signal is a discrete and binary coded version of the message or information.Question 6 ( 1.0 marks) What are the laws of reflection?Question 7 ( 1.0 marks) Name the physical quantity, whose SI unit is Newton coulomb.Question 8 ( 1.0 marks) State two factors by which the range of Transmission of signals by a T.V. tower can be increased.Question 9 ( 2.0 marks) The electric field and electric potential at any point due to a point charge kept in air is 20 NC1 and 10 JC1 respectively. Calculate the magnitude of this charge.Question 10 ( 2.0 marks) Write the mathematical relation between mobility and drift velocity of charge carriers in a conductor. Name the mobile charge carriers responsible for conduction of electric current in (i) an electrolyte (ii) an ionized gas.Question 11 ( 2.0 marks) State the principle of working of a cyclotron. Write two uses of this machine.Question 12 ( 2.0 marks) Draw a labelled ray diagram of a reflecting type telescope. Write its any one advantage over refracting type telescope.Question 13 ( 2.0 marks) Draw and explain the output waveform across the load resistor R, if the input waveform is as shown in the given figure.

ORExplain how the width of depletion layer in a p-n junction diode changes when the junction is (i) forward biased (ii) reverse biased.

Question 14 ( 2.0 marks) The given graph shows the variation of charge q versus potential difference V for two capacitors C1 and C2. The two capacitors have same plate separation but the plate area of C2 is double than that of C1. Which of the lines in the graph correspond to C1 and C2 and why?Question 15 ( 2.0 marks) Two cells E1 and E2 in the given circuit diagram have an emf of 5 V and 9 V and internal resistance of 0.3 and 1.2 respectively.

Calculate the value of current flowing through the resistance of 3 .Question 16 ( 2.0 marks) How is the mutual inductance of a pair of coils affected when:(i) Separation between the coils is increased?(ii) The number of turns of each coil is increased?(iii) A thin iron sheet is placed between the two coils, other factors remaining the same?Explain your answer in each case.Question 17 ( 2.0 marks) QA convex lens made up of glass of refractive index 1.5 is dipped, in turn, in:(i) Medium A of refractive index 1.65(ii) Medium B of refractive index 1.33Explain giving reasons, whether it will behave as a converging lens or a diverging lens in each of these two media.Question 18 ( 2.0 marks) Define the terms threshold frequency and stopping potential in relation to the phenomenon of photoelectric effect. How is the photoelectric current affected on increasing the (i) frequency (ii) intensity of the incident radiations and why?Question 19 ( 3.0 marks) Explain with the help of a nuclear reaction in each of the following cases, how the neutron to proton ratio changes during (i) alpha-decay (ii) beta-decay?Question 20 ( 3.0 marks) What is an intrinsic semiconductor? How can this material be converted into, (i) P-type (ii) N-type extrinsic semiconductor?Explain with the help of energy band diagrams.Question 21 ( 3.0 marks) Why is the mass of a nucleus always less than the sum of the masses of its constituents, neutrons and protons?ORDraw a graph showing the variation of binding energy per nucleon with mass number for different nuclei. Explain, with the help of this graph, the release of energy by the process of nuclear fusion.Question 22 ( 3.0 marks) Define the term modulation. Name three different types of modulation used for a message signal using a sinusoidal continuous carrier wave. Explain the meaning of any one of these.Question 23 ( 3.0 marks) What is electric flux? Write its S.I. units. Using Gausss theorem, deduce an expression for the electric field at a point due to a uniformly charged infinite plane sheet.Question 24 ( 3.0 marks) A 10 m long wire of uniform cross-section and 20 resistances is used in a potentiometer. The wire is connected in series with a battery of 5 V along with an external resistance of 480 . If an unknown emf E is balanced at 6 m length of the wire, calculate:(i) The potential gradient of the potentiometer wire(ii) The value of unknown emf EQuestion 25 ( 3.0 marks) Draw a circuit diagram for use of NPN transistor as an amplifier in common emitter configuration. The input resistance of a transistor is 1000 . On changing its base current by 10 A, the collector current increases by 2 mA.If a load resistance of 5 k is used in the circuit, calculate:(i) The current gain(ii) Voltage gain of the amplifier Question 26 ( 3.0 marks) Define the term critical frequency in relation to sky wave propagation of electromagnetic waves.On a particular day, the maximum frequency reflected from the ionosphere is 10 MHz. On another day, it was found to decrease to 8 MHz. Calculate the ratio of the maximum electron densities of the ionosphere on the two days.Question 27 ( 3.0 marks) Draw a labelled diagram of Hertzs experimental set-up to produce electromagnetic waves. Explain the generation of electromagnetic waves using this set-up.Question 28 ( 5.0 marks) The given circuit diagram shows a series LCR circuit connected to a variable frequency 230 V source.

(a) Determine the source frequency which drives the circuit in resonance.(b) Obtain the impedance of the circuit and the amplitude of current at the resonating frequency.(c) Determine the rms potential drops across the three elements of the circuit.(d) How do you explain the observation that the algebraic sum of the voltages across the three elements obtained in (c) is greater than the supplied voltage?ORThe primary coil of an ideal step-up transformer has 100 turns and the transformation ratio is also 100. The input voltages and the power are 220 V and 1100 W respectively. Calculate:(i) Number of turns in the secondary(ii) The current in the primary(iii) Voltage across the secondary(iv) The current in the secondary(v) Power in the secondaryQuestion 29 ( 5.0 marks) What is interference of light? Write two essential conditions for sustained interference pattern to be produced on the screen.Draw a graph showing the variation of intensity versus the position on the screen in Youngs experiment when (a) both the slits are opened and (b) one of the slit is closed.What is the effect on the interference pattern in Youngs double slit experiment when:(i) Screen is moved closer to the plane of slits?(ii) Separation between two slits is increased. Explain your answer in each case.ORWhat is diffraction of light? Draw a graph showing the variation of intensity with angle in a single slit diffraction experiment. Write one feature which distinguishes the observed pattern from the double slit interference pattern.How would the diffraction pattern of a single slit be affected when:(i) The width of the slit is decreased?(ii) The monochromatic sources of light is replaced by a source of white light?Question 30 ( 5.0 marks) With the help of a neat and labelled diagram, explain the underlying principle and working of a moving coil galvanometer. What is the function of (i) Uniform radial field(ii) Soft iron corein such a device?ORDerive a mathematical expression for the force per unit length experienced by each of the two long current carrying conductors placed parallel to each other in air. Hence define one ampere of current.Explain why two parallel straight conductors carrying current in the opposite direction kept near each other in air repel?closeGalleriesof by

Physics 2006 Set 1 Close

Subjective Test

(i)All questions are compulsory.(ii) There are 30 questions in total. Questions 1 to 8 carry one mark each, Questions 9 to 18 carry two marks each, Question 19 to 27 carry three marks each and Question 28 to 30 carry five marks each.(iii)There is no overall choice. However, an internal choice has been provided.(iv)Wherever necessary, the diagrams drawn should be neat and properly labelled.(v) Use of calculators is not permitted. Question 1 ( 1.0 marks) Define the term dielectric constant of a medium in terms of capacitance of a capacitor.Solution:Dielectric constant of a medium is defined as the ratio of the capacitance of a capacitor with dielectric in between the plates to the capacitance of the same capacitor with vacuum or air in between the plates.Question 2 ( 1.0 marks) Sketch a graph showing variation of resistivity of carbon with temperature.Solution:The resistivity of carbon decreases with increasing temperature as shown in the figure given below.

Question 3 ( 1.0 marks) The vertical component of Earths magnetic field at a place is times the horizontal component. What is the value of angle of dip at this place?Solution:

Angle of dip, = 60Question 4 ( 1.0 marks) With what purpose was famous DavissonGermer experiment with electrons performed?Solution:Davisson and Germer experiment confirmed the wave nature of electrons.Question 5 ( 1.0 marks) Name the type of communication in which the signal is a discrete and binary coded version of the message or information.Solution:Digital communicationQuestion 6 ( 1.0 marks) What are the laws of reflection?Solution:(i) The incident ray, the reflected ray, and the normal lie in the same plane.(ii) The angle of incidence (i) is always equal to the angle of reflection (r). i = rQuestion 7 ( 1.0 marks) Name the physical quantity, whose SI unit is Newton coulomb.Solution:Newton coulomb is the SI unit of electric field intensity.Question 8 ( 1.0 marks) State two factors by which the range of Transmission of signals by a T.V. tower can be increased.Solution:(i) By increasing the height of the tower(ii) By increasing the height of the receiving antenna, so that it may directly intercept the signal from the transmitting antennaQuestion 9 ( 2.0 marks) The electric field and electric potential at any point due to a point charge kept in air is 20 NC1 and 10 JC1 respectively. Calculate the magnitude of this charge.Solution:Here, E = 20 NC1V = 10 JC 1

And Dividing equation (ii) by (i), we obtain

Charge, Question 10 ( 2.0 marks) Write the mathematical relation between mobility and drift velocity of charge carriers in a conductor. Name the mobile charge carriers responsible for conduction of electric current in (i) an electrolyte (ii) an ionized gas.Solution:

(i) The charge carriers in an electrolyte are positive and negative ions.(ii) In an ionised gas, the charge carriers are electrons and positively charged ions.Question 11 ( 2.0 marks) State the principle of working of a cyclotron. Write two uses of this machine.Solution:The working of the cyclotron is based on the fact that positively charged particles such as proton, deuteron, etc. can be accelerated to a sufficiently high energy with the help of smaller values of oscillating electric field by making it to cross the same electric field time and again with the use of strong magnetic field.A cyclotron is used(i) to bombard nuclei with high energy particles and to study the resulting nuclear reaction(ii) to produce radioactive substances, which may be used in hospitals for diagnosis of diseases in the bodyQuestion 12 ( 2.0 marks) Draw a labelled ray diagram of a reflecting type telescope. Write its any one advantage over refracting type telescope.Solution:The ray diagram of a reflecting type telescope is given below:

Its one of the main advantages is that there is no chromatic aberration as the objective is a mirror.Question 13 ( 2.0 marks) Draw and explain the output waveform across the load resistor R, if the input waveform is as shown in the given figure.

ORExplain how the width of depletion layer in a p-n junction diode changes when the junction is (i) forward biased (ii) reverse biased.

Solution:When the input voltage is + 5 V, the diode gets forward biased. The output of + 5 V is obtained across load resistance. When the input voltage is 5 V, the diode gets reverse biased. No output is obtained across R.ORIn forward biasing, the applied voltage V of battery B mostly drops across the depletion region and the voltage drop across the p-side and n-side of the p-n junction is negligible small. It is due to the fact that the resistance of depletion region is very high as it has no free charge carriers. In forward biasing, the forward voltage opposes the potential barrier VB. As a result of it, the potential barrier height is reduced and width of depletion layer decreases.

When a p-n junction is reverse biased, the majority charge carriers flow away from the junction and the width of the depletion layer increases as shown below.

Question 14 ( 2.0 marks) The given graph shows the variation of charge q versus potential difference V for two capacitors C1 and C2. The two capacitors have same plate separation but the plate area of C2 is double than that of C1. Which of the lines in the graph correspond to C1 and C2 and why?Solution:

As i.e., C AThe capacitor having larger area has more capacitance. As the plate C2 is double of that of C1, therefore, C2 has a larger capacitance. Hence, the line A of the graph corresponds to C2.Question 15 ( 2.0 marks) Two cells E1 and E2 in the given circuit diagram have an emf of 5 V and 9 V and internal resistance of 0.3 and 1.2 respectively.

Calculate the value of current flowing through the resistance of 3 .Solution:Net emf of E2 E1 = 9 5 = 4 VTotal resistance = 0.3 + 1.2 + 4.5 + Current through the circuit, Current through the 3 resistance = Question 16 ( 2.0 marks) How is the mutual inductance of a pair of coils affected when:(i) Separation between the coils is increased?(ii) The number of turns of each coil is increased?(iii) A thin iron sheet is placed between the two coils, other factors remaining the same?Explain your answer in each case.Solution:(i) When the separation between the two coils is increased, the flux linked with the secondary due to the current in the primary decreases. Hence, the mutual inductance decreases.(ii) Mutual inductance increases when the number of turns in each coil is increased because M N1 N2.(iii) When an iron sheet is placed between the two coils, the mutual inductance increases because M permeability (r).[Where, r is the relative permeability of the iron sheet]Question 17 ( 2.0 marks) QA convex lens made up of glass of refractive index 1.5 is dipped, in turn, in:(i) Medium A of refractive index 1.65(ii) Medium B of refractive index 1.33Explain giving reasons, whether it will behave as a converging lens or a diverging lens in each of these two media.Solution:(i) Focal length FA in medium A of refractive index 1.65 is given by:

As the focal length (FA) is negative, the lens is diverging.(ii) Focal length (FB) in medium B of refractive index 1.33 is given by:

As the focal length (FB) is positive, the lens is converging.Question 18 ( 2.0 marks) Define the terms threshold frequency and stopping potential in relation to the phenomenon of photoelectric effect. How is the photoelectric current affected on increasing the (i) frequency (ii) intensity of the incident radiations and why?Solution:Threshold frequency:It is the minimum frequency of the incident radiation for which the photoelectrons are just emitted from a metal surface without any kinetic energy.Stopping potential:Stopping potential or cut off potential is that minimum negative potential given to anode in a photocell for which the photoelectric current becomes zero.(i) The photoelectric current is independent of frequency of the incident light. Hence, there is no effect.(ii) With the increase of intensity of the incident radiations, the number of photoelectrons emitted per unit time increases and hence photoelectric current increases.Question 19 ( 3.0 marks) Explain with the help of a nuclear reaction in each of the following cases, how the neutron to proton ratio changes during (i) alpha-decay (ii) beta-decay?Solution:(i) Let us consider the following nuclear reaction:

Neutron to proton ratio before -decay

Neutron to proton ratio after -decay

As , Neutron to proton ratio increases in -decay.(ii) Let us consider the following equation in this case:

Neutron to proton ratio before -decay

Neutron to proton ratio after -decay

As ,Thus, the neutron to proton ratio decreases in -decay.Question 20 ( 3.0 marks) What is an intrinsic semiconductor? How can this material be converted into, (i) P-type (ii) N-type extrinsic semiconductor?Explain with the help of energy band diagrams.Solution:A pure semi-conductor which is free of every impurity is called intrinsic semi-conductor.The electrical conductivity of a pure semi-conductor is totally governed by the number of electrons excited from the valence band to the conduction band and is called intrinsic conductivity.(i) p-type semi-conductor:If we dope intrinsic semi-conductor with a controlled amount of trivalent atoms, then the intrinsic semi-conductor gets converted to p-type semi-conductor.Trivalent impurity atoms will occupy places of some Si-atoms and there will be one incomplete covalent bond with neighbouring Si-atoms, due to the deficiency of an electron.This makes it ionised and creates a hole or an electron deficiency in the covalently bonded electron system in the crystal. The trivalent atoms are called acceptor atoms and this extrinsic semi-conductor is known as p-type semi-conductor.

(ii) n-type semi-conductor:An intrinsic semi-conductor is doped with controlled amount of pentavalent atoms to make it an n-type semi-conductor. This four of the five valence electrons of the impurity atoms will form covalent bonds by sharing the electrons with the adjoining four atoms of silicon while the fifth electron is very loosely bound with the parent impurity atom and is comparatively free to move.Energy band diagram of an n-type semi-conductor is shown in the figure below.

Question 21 ( 3.0 marks) Why is the mass of a nucleus always less than the sum of the masses of its constituents, neutrons and protons?ORDraw a graph showing the variation of binding energy per nucleon with mass number for different nuclei. Explain, with the help of this graph, the release of energy by the process of nuclear fusion.Solution:In the formation of the nucleus, the protons and neutrons have to collect in a very small space whose size is of the order of 1014 m. The energy required for this purpose is spent by the nucleons at the cost of their masses. As a result of this, the mass of the nucleus formed becomes less than the sum of the masses of the individual nucleons.OR

When we move from lighter nuclei to heavier nuclei, we find that there will be gain in the overall binding energy and hence release of energy. This indicates that energy can be released when two or more lighter nuclei fuse together to form a heavy nucleus.Question 22 ( 3.0 marks) Define the term modulation. Name three different types of modulation used for a message signal using a sinusoidal continuous carrier wave. Explain the meaning of any one of these.Solution:Modulation:It is process wherein we superimpose the low audio frequency baseband message or information signals (called the modulating signals) on a high frequency wave (called the carrier wave). The resultant wave is called the modulated wave, which is transmitted.A sinusoidal carrier wave can be modulated in three ways:(i) Amplitude modulation(ii) Frequency modulation(iii) Phase modulationAmplitude modulation:In amplitude modulation, the amplitude of the carrier wave is varied in accordance with the amplitude of the audio frequency modulating signal.However, the frequency of amplitude modulated wave remains the same as that of the carrier wave.Question 23 ( 3.0 marks) What is electric flux? Write its S.I. units. Using Gausss theorem, deduce an expression for the electric field at a point due to a uniformly charged infinite plane sheet.Solution:Electric flux:Electric flux over an area in an electric field represents the total number of field lines crossing this area.

SI unit:Nm2 C1Electric field at a point due to a uniformly charged infinite plane sheet of charge:Consider a thin, infinite plane sheet of charge. Let be the surface density of charge on the sheet. We have to calculate electric field intensity at any point P, (at a perpendicular distance) r from the sheet.

Let us imagine a cylinder of cross-sectional area ds around P and length 2r, piercing through the sheets.Electric flux over these edges

On the curved surface of the cylinder, and outward normal are to each other. Therefore, no contribution to electric flux is made by the curved surface of the cylinder.Total electric flux over the entire surface of the cylinder = 2 EdsAs area of the sheet intercepted by the cylinder is ds,Total charge enclosed by the cylinder = ds According to Gausss law in electrostatics,

Question 24 ( 3.0 marks) A 10 m long wire of uniform cross-section and 20 resistances is used in a potentiometer. The wire is connected in series with a battery of 5 V along with an external resistance of 480 . If an unknown emf E is balanced at 6 m length of the wire, calculate:(i) The potential gradient of the potentiometer wire(ii) The value of unknown emf ESolution:Here, l = 10 mRAB = 20 V = 5 VRext = 780 Current through the wire

Potential drop across the wire IRAB = 0.01 20 = 0.2 VLength of wire AB, l = 10 m(i) Potential gradient is

(ii) Unknown emf,E = kl = 0.02 6 = 0.12 VQuestion 25 ( 3.0 marks) Draw a circuit diagram for use of NPN transistor as an amplifier in common emitter configuration. The input resistance of a transistor is 1000 . On changing its base current by 10 A, the collector current increases by 2 mA.If a load resistance of 5 k is used in the circuit, calculate:(i) The current gain(ii) Voltage gain of the amplifier Solution:

Numerical: GivenRin = 1000 IB = 10 A = 105 AIC = 2 mA = 2 103 ARout = 5 k = 5 103 (i) Current gain

(ii) Voltage gain

Question 26 ( 3.0 marks) Define the term critical frequency in relation to sky wave propagation of electromagnetic waves.On a particular day, the maximum frequency reflected from the ionosphere is 10 MHz. On another day, it was found to decrease to 8 MHz. Calculate the ratio of the maximum electron densities of the ionosphere on the two days.Solution:Critical frequency:It is that highest frequency of radio wave, which when sent straight (that is normally) towards the layer of ionosphere gets reflected from ionosphere and returns to the earth. It is given by [Where Nmax is the maximum electron density of the ionosphere layer]Numerical:fC = 10 MHz,

Question 27 ( 3.0 marks) Draw a labelled diagram of Hertzs experimental set-up to produce electromagnetic waves. Explain the generation of electromagnetic waves using this set-up.Solution:Hertzs Experiment:The following figure shows the Hertzs experimental setup.

Two large metal plates P and are connected to metal spheres S and . The spheres are connected to an induction coil. By interrupting current in the coils, a sudden high voltage is set up across the gap. This voltage ionises the air in the gap, which in turn produces oscillating current in the gap. This process results in the production of electromagnetic waves. These waves are detected by detector, which consists of a single loop of wire connected to sphere G and .Question 28 ( 5.0 marks) The given circuit diagram shows a series LCR circuit connected to a variable frequency 230 V source.

(a) Determine the source frequency which drives the circuit in resonance.(b) Obtain the impedance of the circuit and the amplitude of current at the resonating frequency.(c) Determine the rms potential drops across the three elements of the circuit.(d) How do you explain the observation that the algebraic sum of the voltages across the three elements obtained in (c) is greater than the supplied voltage?ORThe primary coil of an ideal step-up transformer has 100 turns and the transformation ratio is also 100. The input voltages and the power are 220 V and 1100 W respectively. Calculate:(i) Number of turns in the secondary(ii) The current in the primary(iii) Voltage across the secondary(iv) The current in the secondary(v) Power in the secondarySolution:(a)

(b) At resonance Z = R = 40 Current amplitude,

(c)

rms potential drop across resistor R = Irms R

rms potential drop across inductor =

rms potential drop across the capacitor

(d) The algebraic sum of the three voltages is more than the source voltage of 230 V. These voltages are not in the same phase and cannot be added like ordinary numbers. The voltages across L and C are out of phase and get added to zero. Therefore, = Applied rms voltageORGiven: NP = 100, Transformation ratio = 100,VP = 220 V, PP = 100 W(i) = Transformation ratioNS = Transformation ratio NPNS = 100 100 = 10000(ii) (iii) VS = Transformation ratio VP = 100 220 = 22000 V(iv) (v) For an ideal transformer, PS = PP = 1100 WQuestion 29 ( 5.0 marks) What is interference of light? Write two essential conditions for sustained interference pattern to be produced on the screen.Draw a graph showing the variation of intensity versus the position on the screen in Youngs experiment when (a) both the slits are opened and (b) one of the slit is closed.What is the effect on the interference pattern in Youngs double slit experiment when:(i) Screen is moved closer to the plane of slits?(ii) Separation between two slits is increased. Explain your answer in each case.ORWhat is diffraction of light? Draw a graph showing the variation of intensity with angle in a single slit diffraction experiment. Write one feature which distinguishes the observed pattern from the double slit interference pattern.How would the diffraction pattern of a single slit be affected when:(i) The width of the slit is decreased?(ii) The monochromatic sources of light is replaced by a source of white light?Solution:Interference of Light:Interference of light is the phenomenon of redistribution of light energy in a medium on account of superposition of light waves from two coherent sources.Essential conditions for sustained interference are as follows:(i) The two sources of light must be coherent.(ii) The two sources must be narrow.When both the slits are open, we get interference pattern on the screen. The following intensity distribution curve is obtained.

When one of the slits is closed, diffraction pattern is obtained on the screen. The following intensity curve is obtained.

(i) The fringe width () is given by the relation: When screen is moved closer to the plane of the slits, the distance D decreases and the fringe width also decreases.(ii) When separation d between two slits is increased, fringe width decreases.ORDiffraction of light is the phenomenon of bending of light around corners of an obstacle or aperture in the path of light. On account of this bending, light penetrates into the geometrical shadow of the obstacle. The light thus deviates from its linear path.

In interference, all bright fringes are of same intensity. In diffraction, the intensity of bright fringes decreases with the increase in distance from the central bright fringe.(i) When the width of the slit is decreased, the diffraction pattern becomes more pronounced.(ii) When source is emitting white light, the diffraction pattern is coloured. The central maximum is white, but other bands are coloured. As band width is , therefore, red band with higher wavelength is wider than the violet band with smaller wavelength.Question 30 ( 5.0 marks) With the help of a neat and labelled diagram, explain the underlying principle and working of a moving coil galvanometer. What is the function of (i) Uniform radial field(ii) Soft iron corein such a device?ORDerive a mathematical expression for the force per unit length experienced by each of the two long current carrying conductors placed parallel to each other in air. Hence define one ampere of current.Explain why two parallel straight conductors carrying current in the opposite direction kept near each other in air repel?Solution:Principle:Its working is based on the fact that when a current-carrying coil is placed in a magnetic field, it experiences a torque.

Working:Suppose the coil PQRS is suspended freely in the magnetic field.Let, l = Length PQ or RS of the coilb = Breadth QR or SP of the coiln = Number of turns in the coilArea of each turn of the coil, A = l bLet B = Strength of the magnetic field in which coil is suspendedI = Current passing through the coil in the direction PQRSLet at any instant, be the angle, which the normal drawn on the plane of the coil makes with the direction of magnetic field.The rectangular coil carrying current when placed in the magnetic field experiences a torque whose magnitude is given by: = nIBA sin Due to deflecting torque, the coil rotates and suspension wire gets twisted. A restoring torque is set up in the suspension wire.Let be the twist produced in the phosphor bronze strip due to rotation of the coil and K be the restoring torque per unit twist of the phosphor bronze strip. Then,Total restoring torque produced = K In equilibrium position of the coil, deflecting torque = restoring torque NIBA = kOr, Where [constant for a galvanometer]It is known as galvanometer constant.ORConsider two infinitely long thin conductors carrying currents in opposite directions.Magnetic field B1 due to I1 at P on conductor CD is given by:

The magnetic field B1 is perpendicular to plane of paper and directed inward. This field will produce a force/length F2 on conductor CD given by:

By Flemings left hand rule, direction of F2 is away from conductor AB.Similarly the current I2 will create a field B2 at Q directed inward, which in turn will create force/length F1.

By Flemings left hand rule, the direction F1 is away from the conductor CD. Hence, the two conductors repel each other.Definition of Ampere: If I1 = I2 = 1 A and r = 1 m, then

Thus, one ampere is that current which on flowing through each of the two parallel uniform linear conductors placed in free space at a distance of one metre from each other produces between them a force of 2 107 N per metre of their lengths.closeGalleriesof by