Electromagnetic waves Questions and Answers

A cooling object was emitting radiations of time varying wavelength 3000 40t where 2 is in and t is in second is incident on a metal sheet of work function 2eV such that the power incident on sheet is constant at 100 watt This signal is switched on and off for time intervals of 2 minutes and 1 minute respectively Each time the signal is switched on again starts from fresh value of 3000 If the meta plate is grounded so that it always remains neutral and electron clouding is negligible then find the maximum photocurrent mA The photoemission efficiency is 0 01 and remains constant Take hc 12400eV

9 A parallel beam of light of intensity is incident on a cylinder of height h and radius R placed on surface as shown in figure If surface is reflecting then force exerted by beam is F and force exerted by beam is F2 if surface is absorbing A F C F2 8 Rh 3C 21Rh B F D F2 9 hR 4C h 3 Rh C figura

a For many purposes it is necessary to change an alternating voltage from one value to another of greater or smaller value Name the device that can accomplish the above task b Mention any two reasons for energy loss in the above device c Explain how large scale transmission and distribution of electrical energy over long distances is done with the above device d Give reason for the following i At an airport a person is made to walk through the doorway of a metal detector for security reasons If he she carries anything made of metal the metal detector emits a sound On what principle does this detector work ii Why is the use of a c voltage preferred over d c voltage

Two point sources X and Y emit waves of same frequency and speed but Y lags in phase behind X by 2 radian If there is a maximum in direction D the distance XO using n as an integer is given by X 1 n 1 2 X n 1 3 n 1 D

In the figure a line of electric field created by two point charges q and 92 is shown If it is known that q 1 C the charge q2 is closest to a 2 C b 4 C d 8 C c 6 C A conducting shell of radius R has charge Q Electrostatic force between 91 92

An object of mass m 1 kg attached to a string is moving in a circle of radius R 40 cm on a horiozntal surface The other end of the string is threaded through a hole at the centre of the circle and a mass of M 2kg is hung from it Initially the mass M was held at rest If the mass M is released then the closest approach of the mass m to the centre is known to be r 10 cm Then choose the correct options Take g 10m s M A the smallest speed of mass m is 0 9m s B the largest speed of mass m is 3 6m s approximately C acceleration of mass M at the highest point is 6m s D acceleration of mass M at the lowest point is 36m s

Example 8 4 Light with an energy flux of 18 W cm falls on a non reflecting surface at normal incidence If the surface has an area of 20 cm2 find the average force exerted on the surface during a 30 minute time span Solution The total energy falling on the surface is U 18 W cm x 20 cm 30 60 6 48 105 J Therefore the total momentum delivered for complete absorption is U 6 48 105 J 2 16 x 10 kg m s 3x10 m s p c The average force exerted on the surface is p 2 16x10 3 t 0 18x104 F 1 2 10 N

3 25 A system consists of two springs connected in series and having the stiffness coefficients k and k Find the minimum work to be performed in order to stretch this system by x kjk x 2 k k Ans 7

The displacement of a forced oscillator is zero at time t 0 and its rate of growth is governed by the rate of decay of the transient term If this term decays to e k of its original value in a time t show that for small damping the average rate of growth of the oscillations is given by xo t Fo 2kmwo where xo is the maximum steady state displacement Fo is the force amplitude and w s m

Which of the following statement is false for the properties of electromagnetic waves Question Type Single Correct Type 1 2 These waves do not require any material medium for propagation Both electric and magnetic field vectors attain the maxima and minima at the same place and same ti 3 The energy in electromagnetic wave is divided equally between electric and magnetic field vectors

Monochromatic light is beamed into a Michelson inter ferometer The movable mirror is displaced 0 382 mm causing the interferometer pattern to reproduce itself 1700 times Determine the wavelength of the light What color is it

A radiowave has a maximum magnetic field induction of 10 T on arrival at a receiving antenna The maximum electric field intensity of such a wave is 1 zero 2 3 x 10 V m 3 5 8 x 10 9 V m 4 3 3 x 10 3 V m 22 4 Po 26 K The ave given be 1 10 8 2 10 7 3 10 6

a region of free space the electric field at an instant of time is E 24 0 48 0 60 0 N C and the magnetic field is B 0 080 0 290 0 200 a Show that the two fields are perpendicular to each other by calculating the following quantities ExBx 1 92 N T C N T C N T C N T C 13 92 EyBy E B 12 ExBx EyBy E B 0 b Determine the component representation of the Poynting vector for these fields Use three decimal places 11 0 107 18 3 107 21 27 107 W m A

0 Two sound P 2 x 104 sin 2 x 104 t Pa and P 4 x 104 sin 3 x 104 t 6 Pa 2 superimpose with each other Find the amplitude of resultant wave 1 4 47 x 104 Pa 2 4 47 Pa 104 Pa

The voltage wave propagating on a transmission line is given in real space time form as v z t 10cos 4m 108 1 1 6 m2 6cos 4 108 16 m2 the voltage expression in phasor form V 10e 11 62 5e 1 6 m2 OV 10e J 1 6 T2 6e J 1 6 m2 OV 10 11 62 68 1 1 6 m2 Y 10e 11 62 61 1 6 m 2

tomic rigid molecule is kB is Boltzm ann s constant and T is absolute tem perature Options 1 3 2 kB T 2 5 2 kB T 3 kB T 4 7 2 kB T My option 1 Key 2 Status Wrong Pg 330 Class XT NCERT Answer The important point to remember is that

1 A clock in a spaceship emits signal at an interval of 5s as observed b astronaut in the spaceship If the spaceship travels with a speed of 1 8 10 8 m s find the interval between two successive signals as received an observer on the ground 1 Point 6 25s 5s 4s

A 159 2 MHz LHCP electromagnetic wave is propagating in the y direction electric field is found to be 5 V m along the z axis at the origin when t 0 What is corresponding H field of the wave

Why do the properties of anode rays does not depend upon the nature of gas unlike cathode rays Why is the maximum value of e m can be calculated for gas with lower mass Can you explain in simple language

A particle with mass m and total energy Eo travels at a constant velocity V which may approach the speed of light It then collides with a stationary particle with the same mass m and they are seen to scatter elastically at the relative angle with equal kinetic energies a Determine 8 relating it to m and Eo

15 It is better to send 10 000 kW of electric power long distances at 10 000 V rather than at 220 V because A there is less heating in the transmission wires B the resistance of the wires is less at high voltages C more current is transmitted at high voltages D the insulation is more effective at high voltages E the iR drop along the wires is greater at high voltage

Which answer choice best describes which wave property could you change to yield a more energetic wave a Increase the amplitude to increase the wave energy Ob Increase the wavelength to increase the wave energy Oc Decrease the amplitude to increase the wave energy d Decrease the wavelength to increase the wave energy

Q 12 Five capacitors are connected as shown in the figure Initially S is opened and all capacitors are uncharged When S is closed steady state is obtained Then find out potential difference between the points M and N TV 1 14 3 10 S 6 F 4 F M HH N 2 F 4 F 1 2 F 2 12 4 15 31V

According to special theory of relativity the factor y that determine the length contraction and the time dilation is given by Y 1 12 2223 Determine the numerical values of y for an object moving at speed v 0 01c 0 05c 0 10c 0 20c 0 30c 0 35c 0 45c 0 50c and 0 75c

The magnetic field of an EM wave trave lling along X axis is 4 10 4 sin wt kx Here B is in tesla t is in second and x is in meter C alculate the peak value of electric force acting on a particle of charge 5 c travelling with a velocity of 5x105 m s along the Y axis Also cal culate the peak value of magnetic force

4 A small block is shot into each of the four tracks as shown below Each of the tracks rises to the same height The speed with which the block enters the track is the same in all cases At the highest point of the track the normal reaction is maximum in 2001 2M 7 V 10 V b

a infrared point source S of power 1 25 kW as shown in the figure The lateral surface of the rod is perfectly insulated from the surroundings If the cross section A absorbs 80 of the AAJ KA TOPPER incident energy and the temperature difference between the ends of the rod is constant then the rate of heat flow through the rod in steady state is

Find force exerted by light beam of intensity I incident on a cylinder height h and base radius R placed on surface as shown in figure Cylinder is having reflection coefficient 0 8 assum transmission A 38 7Rh 15 C

Figure shows a cylinder containing helium gas at atmospheric pressure with a tightly fitting piston of weight one fourth the force acting due to atmospheric pressure The cylinder is jammed at its bottom A block B is hung by means of a mass less string whose other end is attached to the piston It is observed that the piston just starts sliding next the block B is directly placed above the piston Assuming the piston to move slowly find the fractional volume of the gas compressed fixed A C D

two circular plates each of radius r 12 cm and separated by d 5 0 mm The capacitor is being charged by an external source The charging current is constant current I 0 15 A 00 Find the displacement current across the plates a 1 5 A 015 A

Sachin Tendulkar A projects a ball of mass m towards Virendra Sehwag B of mass 48 m as shown in figure The ball collides with the two vertical walls and when it just passes the wall W its velocity is horizontal Sehwag is standing on a cart of mass m catches the ball at the same level at which the ball is projected After the catch cart starts moving with a velocity 0 3 m s horizontally towards right The initial velocity vector of projection of ball is given by V 10 21 1 m s Find the value of Walls are smooth and there is no friction between cart and ground Sehwag remains fixed with respect to the cart Coefficient of restitution of ball with the walls and the required height is shown in the figure W www 1 2 Am 0 3 4 49m

T The dielectric wavelength constant of a gas of is given the following equation here c is the speed of light in free space and v is the phase velocity Then the group velocity V when v 0 1c is given by b j 5 2 C V 2 1 0 5 2 0 222

In the arrangement shown in the figure there is a horizontal cylindrical uniform but time varying magnetic field increasing at a constant rate A charge particle having charge q and mass m is kept in equilibrium at the top of a spring of spring constant k in such a way that it is on the horizontal line passing through the centr of the magnetic field as shown in figure If the compression in the spring is x the constant rate of varying magnetic field is A B 21 3qR D kx mg 21 qR2kx mg 21 C kx mg qR 51 4qR kx mg reeeer q k AM

An electromagnetic wave has an electric field given by E y t Ex y t 100 0 cos 20y wt where everything is in mks units a What is w b What is the frequency f c What is the wavelength d What is B y t e What is the average energy density of the wave

An emf of 20 V is applied at time t 0 to a circuit containing in series 10 mH inductor and 52 resistor The ratio of the currents at time t and at t 40 s is close to Take e 7 389 1 1 06 2 1 15 3 1 46 4 0 84 T B

A planar loop of wire rotates in a uniform magnetic field Initially at t 0 the plane of the loop is perpendicular to the magnetic field If it rotates with a period of 10 s about an axis in its plane then the magnitude of induced emf will be maximum and minimum respectively

d 2 5 104 26 The sun radiates electromagnetic energy at the rate of 3 9 x 1026 W Its radius is 6 96 x 108 m The intensity of sun light in W m at the solar surface will be a 5 6 106 b 6 4 107 c 4 2 106 d 4 2 107

3 The amplitude of the sinusoidally oscillating electric field of plane wave is 60 V m Then the amplitude of the magnetic field is a 2 10 T c 6 10 T b 6 10 T d 2 10 T

A charge Q is placed on the surface of an original and charged soap bubble of radius r Because of the mutual repulsion of the charged surface the radius increases to a somewhat larger radius R If p be the atmospheric pressure The work done by the bubble in pushing back the atmosphere is given by

m2 d 2 3 x 10 W m2 12 The magnetic field of a beam emerging from a filter facing a flood light is given by 3 W B 12 x 10 8 sin 1 20 x 107 z 3 60 x average intensity of the beam is a 1 71 Wm2 b 2 1 W m 2 c 3 2 W m 2 d 2 9 W m The al 10 5 t T The

SolveLancer Test The mathematical expression for Pointing Vector is given by S Ex B The term S x t always points in the Ho i Negative X direction ii Direction of wave propagation SolveLancer Test a Only i true b i ii both false c i ii both true d Only ii true

co sutin C S Radio carbon dating is done by estimating in specimen the a Amount of ordinary carbon still present b Amount of radio carbon still present c Ratio of amount of 4C to C still present 14 12 12 d Ratio of amount of C to 4C still present

electric field of an EM wave is in the negative z direction and the magnetic field is in the positive y direction Which of the following statements is true Answer A B Your Attempt Rate this question Correct answer Energy is being transported in the positive x direction but half a cycle later When the ele c field is in the opposite directi will be transported in the negative x direction Energy is being transported in the positive x direction and half a cycle later when the electric fi is in the opposite direction it

charged particle with charge q enters a region of constant uniform and mutually orthogonal fields E and B with a velocity v perpendicular to both E and B and comes out without any change in magnitude or direction of v Then AIEEE 2007 a v Ex B B c V ExB E b v BxE B2 d v BxE E tic field with

2 15 Why are microwaves considered suitable for radar systems used in aircraft navigation CBSE Delhi 20 Ans Microwaves are considered suitable for radar systems used in aircraft navigation due to t short wavelength or high frequency

Which of the following conditions would theoretically require infinite voltag O a zero current through a capacitor O b a sudden jump in the current through a capacitor OC zero current through an inductor O d a sudden jump in the current through an inductor

receive about 1 37 kW of energy per square meter from the sun Calculate the electric field associated with the sunlight on the surface of the earth assuming that it is essentially monochromatic with 1 60008

Two charges q and q are situated at a certain distance At the point exactly midway between them electric field and potential both are zero electric field is zero but potential is not zero electric field is not zero but potential is zero neither electric field nor potential is zero

A cobalt rod of susceptibility 1500 Am 1 The permeability of cobalt material is 8 x 10 4 Tm A 1 6 x 10 4 Tm A 1 2 10 Tm A 1 7 10 Tm A 1

Suppose an isolated north pole is kept at the centre of a circular loop carrying a electric current i The magnetic field due to the north pole at a point on the periphery of the wire is B The radius of the loop is a The force on the wire is 1 Nearly 2maiB perpendicular to the plane of the wire 2 2ma B in the plane of the wire 3 paiB along the axis of the wire