Basic Physics Questions and Answers

I t Q 43 A truck of mass M has 4 wheels The surface area of r the metal disc in each wheel is A When brakes are applied the brake shoe in each wheel rubs against the metal disc This produces heat We will assume that this heat is used to heat the disc in the wheel only Each disc has mass m and is made of material of specific heat capacity s One day the truck was going downhill on a road inclined at angle to the horizontal To maintain a constant speed v the driver had to apply brakes The only other dissipative force apart from the brake force on the truck is the air resistance force that is equal to F Assume no heating of discs due to air friction a Find the initial rate of rise of temperature of each metal disc after the brakes are applied Find the final temperature T of the disc assuming that it is a black body and it loses heat only through radia tion Take the atmospheric temperature to be To

ath of the shit is 1 5 x 10 cm 3 2 5 x 10 5 cm 4 In an n p n transistor 2 1 0 x 10 cm 4 1 25 x 10 5 cm 108 electrons enter the emitter in 10 s If 1 electrons are lost in the base the fraction of current that enters the collector and current amplification factor are respectively 1 0 8 and 49 3 0 7 and 50 2 0 9 and 90 4 0 99 and 99 34 461 415 6 1 5 x 105 cm 3 2 5 x 10 5 cm n p n if 10 sa 2 1 0 x 10 cm 4 1 25 x 105 cm 108 1 a en un acte qui fanda 1 0 8 and 49 3 0 7 and 50 2 0 9 and 90 4 0 99 and 99

A vernier calipers has main scale divisions of 1mm each 10 main scale divisions coincide with 8 vernier scale divisions When measuring length of obje zero of vernier lies to immediateright of 5 main scale division and 7th vernier scale division coincides with some division of mainscale The scale is free of zero error Mark the correct statements D Least count of calipers is 0 25 mm Measurement of object is 5 25 mm Measurement of object is 5 75 mm 7 Vernier scale coincides with14 main scale division

The yalue of numerical aperature of the objective lens of a microscope is 1 25 If light of wavelength 5000 is used the minimum separation between two points to be seen as distinct will be JEE Main 2019 April 4 0 38 um 1 0 24 m 2 0 48 m 3 0 12 m

40 g of ice at 20 C is dropped into a calorimeter containing 40 g water at 10 C The specific heat of water is twice that of ice The amount of water contained in the calorimeter when equilibrium is reached is

3 10 J If the electric potential at a certain distance from a point charge is 900V and electric intensity is 225 Vm The charge is 1 4 10 C 3 4 10 C 2 2 10 C 4 2 10 C work in carry

15 A student measures the distance traversed in free fall of a body initially at rest in a given time He uses this data to estimate g the acceleration due to gravity If the maximum percentage errors in measurement of the distance and the time are e and e respectively the maximum percentage error in the estimation of g is 1 e e 3 e en 2 e 2e 4 e 2e H

Three forces act on an object a mass of 5 kg as shown in the below Figure F 350 N 40 F2 450 N 35 84 84 m s2 63 82 m s2 F3 600 N Determine both the magnitude of the object s acceleration O 0 m s O O O 70 m s

A charge having e m equal to 108 C kg and with velocity 3 x 105 m s enters into a uniform magnetic field B 0 3 tesla at an angle 30 with direction of field The radius of curvature will be 1999 0 01 cm 0 5 cm 1 cm 2 cm

Examine the following four statements i Surface tension is due to cohesion only norbindel Capillarity is due to adhesion only Surface tension is due due cohesion and adhesion Capillarity is due to both cohesion and adhesion Which of the above statements are true i and ii ii and iii i and iv only iv ii iii iv a b c d to to both

dipole is fixed at the origin with its moment pointing in the X direction Consider two identical circular disc shaped imaginary surfaces with their centres at two points A and B on the X axis equidistant from the origin shown in the figure The surfaces are perpendicular to the X axis The electric flux through the surfaces is and respectively The sign of flux is taken positive if it crosses a surface towards the X direction and take negative if it crosses a surface towards the X direction Which of these options is correct O 0 QL L B 0 and 0 and 0 and 0 and 3 0 3 0 g 0 B 5 0

Two blocks A and B are connected by a massless string shown in figure A force of 30 N is applied on block B The distance travelled by centre of mass in 2 s starting from rest is A 10 kg Smooth B 20 kg

For a vertical semi circular plate sub merged in a homogenous liquid with its diameter d at the free surface the depth of centre of pressure from the free surface is a b c d PRESS 3rd 32 3d 2 4d 3 3rd 16 d

Ira volume rm conductor of length cross section area A and resistivity p is connected with an ideal DC battery of emf then choose the correct option s Assumen to be no of e per L Current in conductor is EA pl Electric field produced in conductor is l Drift velocity of e s in conductor is plen

52 A ball of mass 5 g and charge 10 7 C moves from point A whose potential is 500 V to a point B whos potential is zero The velocity of the ball at t point B if its velocity at the point A is zero is 2 0 1414ms 1 0 1414 cms 1114 cms 1 41 414

4 9 10 ms 2 towards east 46 Two electric charges Qand 40 are seperated by a certain distance If the electric intensity at Qis E the electric intensity at the other charge is 2 5 4 3 E 1 4E 4 2E 48 Two point charges q and q 2 are situated at 0 respectively 2

In the given circuit R is a pure resistor and L is a pure inductor S is a 100V 50 Hz AC Source and A is an ammeter reading is I If the source is changed to 100V 100 Hz the ammeter reading with k and k closed will respectively be S A k R k L

A very long straight wire carries a current At the instant when a charge Q at point P has velocity as shown the force on the charge is I Q P 2005 along Oy YA L opposite to Oy along Ox x

3 A glass bubble from an explosion under water oscillates with a period T proportional to Pa do Ec where P is the static pressure d is the density and E is the total energy of the explosion Find the values of a b and c

When light of wavelength 500 nm is incident on a metal surface of work function 1 83 eV photoelectrons are emitted A fastest photoelectron combines with a He2 atom to form Het atom The Het atom thus formed is in its first excited state Find the energy in eV of the photon emitted during the combination

A gas is undergoes a process in which pressure of gas is P and volume of gas V are related as VPn constant then choose the correct statement s P Bulk modulus of gas is Volume expansion coefficient is Work done in process is I n n 1 T l dW n VdP

49 A electric field of 1 5x10 NC two parallel plates of length 2 cm An electron enters the region between the plates at right angles to the field with a kinetic energy of Ex 2000eV The deflection that the electron experiences at the deflecting plates is 1 0 34 mm 2 0 57 mm 3 7 5 mm 4 0 75 mm 2

4 Mirror is convex m 2 An atomic power nuclear reactor can deliver 19 300 MW The energy released due to fission of each nucleus of uranium atom U23 is 170 MeV The number of uranium atoms fissioned per hour will be Approximately 1 30 x 1025 3 10 x 100 An insulated box containing a diatomic gas of 2 4 1022 4 5 x 10 5 20 4 34 m 2 300 MW face 170 MeV 12 facefuca tan g 2 4 x 102 4 5 x 10 5 1 30 x 1025 3 10 x 1020 af FOREN FIER FO

A body is projected horizontally from the top of tower with a velocity of 20ms 1 After what time the vertical component of velocity is 3 times the horizontal component of velocity g 10ms A 12sec B 6s C 4sec D 2sec Mark For Review Next Save Next Clear Response Submit PHYSICS 101 102 103 104 105 106 107 108 109 110

There are nelectrons of charge e in a drop of of density p It is in equilibrium in an elect field E Then the radius of drop is 1 3 2neE 4 pg 3neE 4 pg 1 2 1 3 2 4 neE pg 1 2 2neE t pg 1 3

In the circuit shown the battery is ideal and both capacitors are initially uncharged If the switch Sis closed the current through the switch immediately afterwards and the current through it after a long time is respectively R S V 3V 3R R C 31 P R 3R 31 R 2002 31 R N U www

A boat crosses river of width 60 7 m inshortest possible path Speed of river is 8m s and speed of the boat in still water is 6m s Find the time taken by boat in seconds to cross the river

A leak proof cylinder of length 1m made of a metal which has very low coefficient of expansion is floating vertically in water at 0 C such that its height above the water surface is 20 cm When the temperature of water is increased to 4 C the height of the cylinder above the water surface becomes 21 cm The density of water at T 4 C relative to the density at T 0 C is close to 1101 2 1 04 1 3 1 03 4 1 26

D The mass of the sphere is 3 2x10kg and it carries a net charge equal to that of 10 electrons If the electronic charge is 1 6 10 C and the acceleration of free fall is 10ms2 the field required to keep the sphere stationary is 1 5 10 V m 3 2 10 V m 2 5 10 V m 4 2 10 V m

A conducting rod AB is moved with velocity v over a U shaped conducting rail placed in a uniform magnetic field as shown in the figure below The motion of rod AB is perpendicular to the direction of magnetic field Then which of the following statements are true Magnetic field Direction into the plane of paper X X X X X X XX XXX X X X X X X X XXX X X X X x X A XXX X X X X B8 B 1 Current in rod will flow from B to A ii Current in rod will flow from A to B iii B point will have high potential iv A point will have high potential XXX XX

A single conservative force acts on a 1 kg particle that moves along x axis The potential energy of the particle varies with x as U 20 x 2 here U is in joules and x is in meters When the particle is at x 5 m its kinetic energy is 20 J then which of the following is are Correct Mechanical energy of particle is 49 J Least and greatest value of x between which particle can move is 2 29 m and 2 29 m respectively Maximum kinetic energy of the particle is 29 J At x 2 the body is in equilibrium

A cannon installed at the top of a hill can fire shells in all directions There is an enemy bunker at an angle of elevation op and a distance d from the cannon All the shells fired explode in air in time T before they reach the bunker At what angle to the horizontal should a shell be fired with a speed u to explode closest to the bunker Acceleration due to gravity is g C tan tan o 2gT

4 We 38 An electron moving along positive x axis with speed of 3x10 m s enters the region of a unifor electric field The electron stops after travelling distance of 90mm in the field The electric fie strength is charge on electron 1 6x10 19 C Mass of electron 9 1 10kg 1 2 84 KV m along ve x axis 2 0 284 KV m along ve x axis 3 0 284 KV m alon ve x axis 1 Lalong twe Y avis

Q 17 54 Suppose we have an unlimited number of identical bulbs Each bulb consumes power 4 W if it is operated at a potential difference 40 V We also have a battery of emf 60 V and internal resistance 89 The minimum number of bulbs that must be connected in parallel across this battery such that each bulb consumes power less than 4 W is

is held in quilibrium by a potential difference of 600V An oil drop carrying Anween the horizontal plates In order to hold another drop of twice the radius in equilibrium a potential drop of 1600V had to be maintained The charge on the second drop is 30 2 2Q 4 3Q 2 all water drops each of radius r and

A 50 kg load is to be pulled up a plane inclined at an angle of 45 with the horizontal with a force making an angle of 30 with the inclined plane If the coefficient of friction is 0 3 what will be the magnitude of the force required to push the load up at the same angle instead of pulling it Ans 640 N

Q 7 54 Two thin conducting spherical shells of radii R and 3R are fixed concentrically and given total charge Q and Q respectively Which of these options is are correct The electric field at a point at a distance 2R from the their common centre has Q and is directed 16 R magnitude radially inward The electric field inside the inner shell is zero The potential at their common centre is 6R The potential of the outer shell is zero

Adipole is placed inside a cavity of a solid conducting neutral body Mark the correct statements A Electrostatic potential of a point on the surface of cavity is same as that of a point on the outer surface of conductor C Everywhere outside the body electric field due to dipole is zero B No charges are induced on the outer surface of conducting body D Everywhere outside the body net electric field is zero

Q 3 54 A small dipole is fixed at the origin with its moment pointing in the X direction Consider two identical circular disc shaped imaginary surfaces with their centres at two points A and B on the X axis equidistant from the origin shown in the figure The surfaces are perpendicular to the X axis The electric flux through the surfaces is and B respectively The sign of flux is taken positive if it crosses a surface towards the X direction and taken negative if it crosses a surface towards the X direction Which of these options is correct 04 0 A P A 0 and B 0 1 0 and B 0 A 0 and g 0

A circular coil of 50 turns and radius 7 cm is placed in a uniform magnetic field of 4 T normal to the plane of the coil If the current in the coil is 6A then total torque acting on the coil is A 14 78 Nm B 0 C 7 39 Nm D 3 69 Nm

A charge moving with velocity v in X direction is subjected to a field of magnetic induction in negative X direction As a result the charge will 1993 remain unaffected start moving in a circular path Y Z plane retard along X axis

f A double slit of separation 0 1 mm is illuminated by white 17 0 1 mm at for light A coloured interfernce pattern is formed on a screen OITeI 100 cm X T V ra tr m ve trta antene XANH TE 100 cm away If a pin hole is located in this screen at a fefe 2 mm distance of 2 mm from the central fringe the wavelengths in the visible spectrum 4000 to 7000 which will be absent in the light transmitted through the pin hole is are 1 4000 fox 4000 7000 f 2 5000 3 6000 4 7000 fox A 1 4000 2 5000 3 6000 4 7000 A

they are collinear et three vectors a b and are related as a b c The angle between a and 6 is 0 Select the orrect alternative Angle between and 6 is greater than 0 2 if b Angle between c and is greater than 0 2 if a b 1 Angle between and 6 can be n 0 for some values of a b Angle between c and 5 cannot be 0 for some values of a b

10 Two identical pendulums A from the some point Both are given positive cahrge with A having more charge than B They diverge and reach equilibrium with the suspension of A and B making angles and O with the vertical respectively 1 0 0 2 0 0 3 0 0

through a point are same 4 Both 1 3 Choose the correct statement 1 In a straight line motion a particle can increase its velocity with decreasing acceleration 2 In a straight line motion acceleration can revert its direction without its velocity reverting its direction 3 A body at rest may be accelerated 4 All of these alat 4 1 a 3 far 1 tetan YES THAT AR FUT 2 anat fend faudra fanu faci a fem fa af 3 farm 4

In a two level laser the population of atoms in the upper and lower levels are 6 5 10 6 and 5 0 10 5 respectively If the coefficient of stimulated emission is 3 2 104 m W s and the energy density is 8 2 J m Hz then calculate the rate of the stimulated emission a 1 7 10 2 S 1 b 1 3x1022 s c 2 2 10 2 S d 1 3x1024 S 1

The diffusivity of the gas O2 CCl4 is being determined by observing the steady state evaporation of carbon tetrachloride into a tube containing oxygen Arnold Cell The distance between the CCl4 liquid level and the top of the tube is 17 1 cm The total pressure on the system is 755 mm Hg and the temperature is O C The vapor pressure of CCl4 at that temperature is 33 0 mm Hg The cross sectional are of the cell is 0 82 cm It is found that 0 0208 cm of CCl4 evaporate in a 10 hr period after steady state has been attained What is the diffusivity of the gas pair O2 CC14

A uniform electric field of magnitude E 100NC exists in space in X direction The field through a plane square flux of this are of edge 10cm placed in the YZ plane Taking the normal along the positive x axis to be positive is A 10 Nm C Nm C 1 C B 100 D 0 1 Nm C Nm C

Figure shows static equilibrium situation friction is adequate to prevent slipping The body is a disc with a point mass attached as its periphery The disc will be in static equilibrium if O O m m Msin 0 cos0 sin 0 M cos 0 cos 0 sin 0 M sin 0

Electric charges are distributed in a small volume The flux of electric field through a spherical surface of radius 10cm surrounding the total charge is 25V m The flux over a concentric sphere of radius 20cm will be A 25V m C 100 V m B 50 V m D 200 V m