Answer & Solution Physics NEET-2017

Transcription

1 nswer & Solution Physics NEET-7 9. Two blocks and of masses m and m respectively are connected by a massless and inextensible string. The whole system is suspended by a massless spring as shown in figure. The magnitudes of acceleration of and immediately after the string is cut, are respectively. g () g, () g,g Sol. [] efore fter m m () g, g (4) g g, kx 4 mg m mg T mg T mg m mg kx 4 mg 4mg mg m am g / mg T m T m mg a m g mg m 9. The acceleration due to gravity at a height km above the earth is the same as at a depth d below the surface of earth. Then: () d km () d km () d km (4) d km h Outside the earth, g g d Inside the earth, g g for same value of g, h d d h km 9. particle executes linear simple harmonic motion with an amplitude of cm. When the particle is at cm from the mean position, the magnitude of its velocity is equal to that of its acceleration. Then its time period in seconds is: () 5 π () 5 π t distance x from mean position, ω x ω x () 4 π 5 (4) π orporate Office : 7, ajiv Gandhi Nagar, (ehind INOX), Kota (aj.) ranch Office :,District entre, (Opp. llen), Jawahar Nagar,Kota (aj.) ontact No. : , info@turningpointkota.com

2 nswer & Solution Physics NEET-7 x ω x x 5 x ω π 4π T sec ω The resistance of a wire is '' ohm. If it is melted and stretched to 'n' times its original length, its new resistance will be: () n () () n (4) n n Volume of wire remain same, thus V Or, ρ ρ V or ' n 95. capacitor is charged by a battery. The battery is removed and another identical uncharged capacitor is connected in parallel. The total electrostatic energy of resulting system: () increases by a factor of 4 () decreases by a factor of () remains the same (4) increase by a factor of Sol. [] Initial energy of system, U i V V when another capacitor is connected in parallel, V' V' V V V ' final energy of system, U f ()V' V 4 orporate Office : 7, ajiv Gandhi Nagar, (ehind INOX), Kota (aj.) ranch Office :,District entre, (Opp. llen), Jawahar Nagar,Kota (aj.) ontact No. : , info@turningpointkota.com

3 nswer & Solution Physics NEET Two rods and of different materials are welded together as shown in figure. Their thermal conductivities are K and K. The thermal conductivity of the composite rod will be: T K K T () K K (K K ) () () K K (4) (K K ) Sol. [] Since rods are in parallel, then K() K K d d d K K K 97. The two nearest harmonics of a tube closed at one end and open at other end are Hz and 6 Hz. What is the fundamental frequency of the system. () Hz () Hz () Hz (4) 4 Hz Sol. [] For closed organ pipe, difference in successive frequencies is equals to twice of fundamental frequency. Then, f 4 f Hz d 98. The bulk modulus of a spherical object is ''. If it is subjected to uniform pressure 'p', the fractional decrease in radius is: () P () () p P (4) p P V P P Since, or V / V V r V P r V e 99. physical quantity of the dimensions of length that can be formed out of c, G and 4π [c is velocity of light, G is universal constant of gravitation and e is charge]: () Sol. [] L e G π c 4 / r p q e K[c] [G] 4πε () c G 4 e π / p q r M LT LT M L T M L T q r q r p q r 6q p and p q r p 4q () e c G4π / (4) e G c 4π is orporate Office : 7, ajiv Gandhi Nagar, (ehind INOX), Kota (aj.) ranch Office :,District entre, (Opp. llen), Jawahar Nagar,Kota (aj.) ontact No. : , info@turningpointkota.com

4 nswer & Solution Physics NEET-7 y solving them, p, q and r Thus, Ge πε L K 4 where K is a dimensionless constant. Figure shows a circuit that contains three identical resistors with resistance 9. each, two identical inductors with inductance L. mh each, and an ideal battery with emf 8 V. The current 'i' through the battery just after the switch closed is... L L Sol. () m (). () (4) ampere [onus] L L when switch is closed, inductor provides infinite resistance and capacitor provides zero resistance. Thus, current through battery, ε E I 4 /. One end of string of length l is connected to a particle of mass 'm' and the other end is connected to a small peg on a smooth horizontal table. If the particle moves in circle with speed ' ', the net force on the particle (directed towards center) will be (T represents the tension in the string) mυ mυ () T () T () T (4) Zero Sol. [] Net force on the particle mv T. The photoelectric threshold wavelength of silver is 5 m. The velocity of the electron ejected from a silver surface by ultraviolet light of wavelength 56 m is: (Given h evs and c 8 ms ) 5 () 6 ms 6 ().6 ms () Sol. [], [] 6 ms (4) 6. ms orporate Office : 7, ajiv Gandhi Nagar, (ehind INOX), Kota (aj.) ranch Office :,District entre, (Opp. llen), Jawahar Nagar,Kota (aj.) ontact No. : , info@turningpointkota.com 4

5 nswer & Solution Physics NEET-7 hc 4 φ.8 ev λ 5 Kinetic energy of electrons, hc K φ λ 4..8 ev.7 9 J V.6 m/s 6 m/s 9.. adioactive material '' has decay constant '8 ' and material '' has decay constant ' '. Initially they have same number of nuclei. fter what time, the ratio of number of nuclei of material '' to that '' will be e? () λ Sol. [] fter time t, Since, & N N e () N N 7λ N e λ N e λ λt e e λ t e λ λ t t λ λ 7λ ( ) t t () 8λ (4) 9λ 4. rope is would around a hollow cylinder of mass kg and radius 4 cm. What is the angular acceleration of the cylinder if the rope is pulled with a force of N? () 5 m/s ().5 rad/s () 5 rad/s (D) 5 m/s N τ F F α 5 rad/s I m m.4 5. Two cars moving in opposite directions approach each other with speed of m/s and 6.5 m/s respectively. The driver of the first car blows a horn having a frequency 4 Hz. The frequency heard by the driver of the second car is [velocity of sound 4 m/s]: () 5 Hz () 6 Hz () 4 Hz (4) 448 Hz V S V O V V V V S 4 O f ' f 4 orporate Office : 7, ajiv Gandhi Nagar, (ehind INOX), Kota (aj.) ranch Office :,District entre, (Opp. llen), Jawahar Nagar,Kota (aj.) ontact No. : , info@turningpointkota.com 5

6 nswer & Solution Physics NEET Hz Turn rectangular coil of length. cm and width.5 cm carries a current of 85 and subjected to a magnetic field of strength.85 T. Work done for rotating the coil by 8 against the torque is: () 9. J () 4.55 J (). J (4).5 J Sol. [] W M cos cos8 M ( ) (NI) µ J 9.5 J long solenoid of diameter. m has 4 turns per meter. t the centre of the solenoid, a coil of turns and radius. m is placed with its axis coinciding with the solenoid axis. The current in the solenoid reduces at a constant rate to from 4 in.5 s. If the resistance of the coil is, the total charge flowing through the coil during this time is: () () 6 () (4) 6 Magnetic field inside the solenoid, ni 7 4 4π I 8π I harge flowing through the ring, φ N( ) πr q 8π (4 ) π π 4 µ 8. Suppose the charge of a proton and an electron differ slightly. One of them is e, the other is (e e). If the net of electrostatic force and gravitational force between two hydrogen atoms placed at a distance d (much greater than atomic size) apart is zero, then e is of the order of [Given mass of hydrogen m h.67 7 kg] () e e e e e e () () 7 (4) 47 Ke(e e) Ke K(e e) Gm r r r r e e Ke Gm e e Ke Gm e e e Ke e e e e Gm e orporate Office : 7, ajiv Gandhi Nagar, (ehind INOX), Kota (aj.) ranch Office :,District entre, (Opp. llen), Jawahar Nagar,Kota (aj.) ontact No. : , info@turningpointkota.com 6

7 nswer & Solution Physics NEET-7 ( ) 7 Gm e K 9 9. Two astronauts are floating in gravitational free space after having lost contact with their spaceship. The two will: () keep floating at the same distance between them () move towards each other () move away from each other (4) will become stationary Sol. [] They have same velocity when separates from spaceship, thus distance will remain same.. The ratio of wavelengths of the last line of almer series and the last line of Lyman series is: () () () 4 (4).5 Last line of almer series, λ Last line of Lyman series, λ λ 4 λ. The de-roglie wavelength of a neutron in thermal equilibrium with heavy water at a temperature T (Kelvin) and mass m, is: h h h h () () () (4) mkt mkt mkt mkt Sol. [] λ λ λ λ m(ke) mkt m KT. thin prism having refracting angle is made of glass of refractive index.4. This prism is combined with another thin prism of glass of refractive index.7. This combination produces dispersion without deviation. The refracting angle of second prism should be: () 4 () 6 () 8 (4) Sol. [] for dispersion without deviation, ( µ ) ( µ ' ) ' µ.4 ' 6 µ '.7. Thermodynamic processes are indicated in the following diagram. orporate Office : 7, ajiv Gandhi Nagar, (ehind INOX), Kota (aj.) ranch Office :,District entre, (Opp. llen), Jawahar Nagar,Kota (aj.) ontact No. : , info@turningpointkota.com 7

8 nswer & Solution Physics NEET-7 P i IV f I III II f f f 7 K 5 K K V Match the following : olumn- olumn- P. Process I a. diabatic Q. Process II b. Isobaric. Process III c. Isochoric S. Process IV d Isothermal () P a, Q c, d, S b () P c, Q a, d, S b () P c, Q d, b, S a (4) P d, Q b, a, S c Sol. [] Theory based 4. U tube with both ends open to the atmosphere, is partially filled with water. Oil, which is immiscible with water, is poured into one side until it stands at a distance of mm above the water level on the other side. Meanwhile the water rises by 65 mm from its original level (see diagram). The density of the oil is: Oil Pa 65 mm 65 mm F E D Pa mm Final water level Initial water level Water () 65kg m () Pressure at Pressure at P ρ g(4) P ρ g() w ρ 98kg / m 4 45kg m () 8kg m (4) 98kg m 5. spring of force constant k is cut into lengths of ratio : :. They are connected in series and the new force constant is k'. Then they are connected in parallel and force constant is k". Then k' : k" is: () : 6 () : 9 () : (4) : 4 K '(6L) K (L) K (L) K (L) K 6K ', K K ' & K K ' when connected in parallel, K" K K K K ' orporate Office : 7, ajiv Gandhi Nagar, (ehind INOX), Kota (aj.) ranch Office :,District entre, (Opp. llen), Jawahar Nagar,Kota (aj.) ontact No. : , info@turningpointkota.com 8

9 nswer & Solution Physics NEET-7 K ' K" 6. Which of the following statements are correct? (a) entre of mass of a body always coincides with the centre of gravity of the body. (b) entre of mass of a body is the point at which the total gravitational torque on the body is zero. (c) couple on a body produce both translational and rotational motion in a body. (d) Mechanical advantage greater than one means that small effort can be used to lift a large load. () (b) and (d) () (a) and (b) () (b) and (c) (4) (c) and (d) Sol. [] Theory based 7. beam of light from a source L is incident normally on a plane mirror fixed at a certain distance x from the source. The beam is reflected back as a spot on a scale placed just above the source L. When the mirror is rotated through a small angle the spot of the light is found to move throught a distance y on the scale. The angle is given by: () Sol. [] y x () y x y () x y (4) x y eflected beam rotates by angle when mirror is rotated by angle. y y Since, θ θ x x 8. gas mixture consists of moles of O and 4 moles of r at temperature T. Neglecting all vibrational modes, the total internal energy of the system is: () 4 T () 5 T () 9 T (4) T f Since, E nt 5 E ()()T (4)()T T 9. onsider a drop of rain water having mass g falling from a height of km. It hits the ground with a speed of 5 m/s. Take 'g' constant with a value m/s. The work done by the (i) gravitational force and the (ii) resistive force of air is: () (i) J (ii) 8.5 J () (i).5 J (ii) 8.5 J () (i) J (ii) 8.75 J (4) (i) J (ii) 8.75J orporate Office : 7, ajiv Gandhi Nagar, (ehind INOX), Kota (aj.) ranch Office :,District entre, (Opp. llen), Jawahar Nagar,Kota (aj.) ontact No. : , info@turningpointkota.com 9

10 nswer & Solution Physics NEET-7 Work done by gravity, w mgh J g by work energy theorem, wg w mv w ( )(5) J. carnot engine having an efficiency of as heat engine, is used as a refrigerator. If the work done on the system is J, the amount of energy absorbed from the reservoir at lower temperature is: () J () 9 J () 99 J (4) J Sol. [] η Since, β 9 η Q Q β 9 Q 9J work done. n arrangement of three parallel straight wires placed perpendicular to plane of paper carrying same current 'I' along the same direction is shown in Fig. Magnitude of force per unit length on the middle wire '' is given by: d d 9 () µ i πd F () µ i πd () µ i πd (4) µ i πd F Ftotal F µ µ I π I d πd orporate Office : 7, ajiv Gandhi Nagar, (ehind INOX), Kota (aj.) ranch Office :,District entre, (Opp. llen), Jawahar Nagar,Kota (aj.) ontact No. : , info@turningpointkota.com

11 nswer & Solution Physics NEET-7. The x and y coordinates of the particle at any time are x 5t t and y t respectively, where x and y are in meters and t in seconds. The acceleration of the particle at t s is: () () 5 m/s () 4 m/s (4) 8 m/s dx ˆ dy V i ˆj (5 4t)i ˆ ˆj dt dt dv and a 4i ˆ dt or a 4 m/s. The ratio of resolving powers of an optical microscope for two wavelengths 4 Å and 6 Å is: () 8 : 7 () 9 : 4 () : (4) 6 : 8 esolving power of microscope λ λ the ratio of resolving power 6 λ 4 4. Preeti reached the metro station and found that the escalator was not working. She walked up the stationary escalator in time t. On other days, if she remains stationary on the moving escalator, then the escalator takes her up in time t. The time taken by her to walk up on the moving escalator will be: t t tt tt () () () (4) t t t t t t When escalator is not working d V...() t when she stand and escalator in moving. d V...() t when they both moves upward d ( V V )...() t ' from eq. (), () and () d d d t t t ' tt t ' t t 5. spherical black body with a radius of cm radiates 45 watt power at 5 K. If the radius were halved and the temperature doubled, the power radiated in watt would be : () 5 () 45 () (4) 8 orporate Office : 7, ajiv Gandhi Nagar, (ehind INOX), Kota (aj.) ranch Office :,District entre, (Opp. llen), Jawahar Nagar,Kota (aj.) ontact No. : , info@turningpointkota.com

12 nswer & Solution Physics NEET-7 s power T 4 r 4 P T r 4 P T r 4 45 T r P 4 r (T) P 8 watt 6. potentiometer is an accurate and versatile device to make electrical measurements of E.M.F. because the method involves: () cells () potential gradients () a condition of no current flow through the galvanometer (4) a combination of cells, galvanometer and resistances onceptual 7. The given electrical network is equivalent to: Y () ND gate () O gate () NO gate (4) NOT gate y y y y y 8. In a common emitter transistor amplifier the audio signal voltage across the collector is V. The resistance of collector is K. If current gain is and the base resistance is k, the voltage and power gain of the amplifier is: () and () 5 and () 5 and 5 (4) and β Voltage gain v v 5 Power gain Voltage gain urrent gain β β 5 9. Two discs of same moment of inertia rotating about their regular axis passing through centre and perpendicular to the plane of disc with angular velocities and. They are brought orporate Office : 7, ajiv Gandhi Nagar, (ehind INOX), Kota (aj.) ranch Office :,District entre, (Opp. llen), Jawahar Nagar,Kota (aj.) ontact No. : , info@turningpointkota.com

13 nswer & Solution Physics NEET-7 into contact face to face coinciding the axis of rotation. The expression for loss of energy during this process is: () I( ) ω ω () I( ) 4 ω ω () I( ω ω ) (4) I( ) 8 ω ω Sol. [] s angular momentum in conserved therefore L L i f Iω Iω I ω ' ω ω ω ' Intial KE is Iω Iω ω ω Final KE is (I) loss intial KE final KE ω ω I( ω ω ) I I( ω ω ) 4 a m. Young's double slit experiment is first performed in air and then in a medium other than air. It is found that 8 th bright fringe in the medium lies where 5 th dark fringe lies in air. The refractive index of the medium is nearly: ().5 ().59 ().69 (4) β m βa λ md 9 λad 8 d d λ 6 λ a 6 or µ.78 λ 9 λ 9 m. Which one of the following represents forward bias diode? V V 4 V () () V V () V () V 5V Zero volt is higher potential than volt.. Two Polaroids P and P are placed with their axis perpendicular to each other. Unpolarised light I is incident on P. third polaroid P is kept in between P and P such that its axis makes an angle 45 with that of P. The intensity of transmitted light through P is : orporate Office : 7, ajiv Gandhi Nagar, (ehind INOX), Kota (aj.) ranch Office :,District entre, (Opp. llen), Jawahar Nagar,Kota (aj.) ontact No. : , info@turningpointkota.com

14 nswer & Solution Physics NEET-7 I () I () 4 I () 8 I (4) 6 45 I I I I I I I & I I cos 45 4 I and I I cos In an electromagnetic wave in free space that root mean square value of the electric field is E rms 6V/m. The peak value of the magnetic field is: ().4 8 T ().8 8 T ().7 8 T (4) 4. 8 T Sol. [] Erms 6 8 rms T T rms 4. If θ and θ be the apparent angles of dip observed in two vertical planes at right angles to each other, then the true angle of dip θ is given by: () cot θ cot θ cot θ () tan θ tan θ tan θ () cot θ cot θ cot θ (4) tan θ tan θ tan θ Sol. [] tan θ tan θ tan θ & tan θ cos α cos(9 α) where, is actual dip angle cos α sin α tan θ tan θ tan θ tan θ cot θ cot θ cot θ 5. The diagrams below show regions of equipotentials V 4 V V 4 V V V V 4 V V V V V V 4 V V V positive charge is moved from to in each diagram. () Maximum work is required to move q in figure (c) orporate Office : 7, ajiv Gandhi Nagar, (ehind INOX), Kota (aj.) ranch Office :,District entre, (Opp. llen), Jawahar Nagar,Kota (aj.) ontact No. : , info@turningpointkota.com 4

15 nswer & Solution Physics NEET-7 () In all the four cases the work done is the same () Minimum work is required to move q in figure (a) (4) Maximum work is required to move q in figure (b) Sol. [] Since, W q V q(v V ) q(4 ) q work done is same in all the four cases. orporate Office : 7, ajiv Gandhi Nagar, (ehind INOX), Kota (aj.) ranch Office :,District entre, (Opp. llen), Jawahar Nagar,Kota (aj.) ontact No. : , info@turningpointkota.com 5