Basic Physics Questions and Answers

d 2 64 52 57 Two metal wires of identical dimensions are connected in series Ifg and o are the conductivities of the metals respectively the effective conductivity of the combination is a 0 0 c 0 0 b d 0 0 2 20 0 0 0

The radius of Na ion is 116 pm and that of CI ion is 167 pm The volume of NaCl unit cell is Question Type Single Correct Type 1 2 3 4 1 81 x 10 22 cm 1 81 x 108 cm 1 81 x 10 cm 1 81 x 10 8 cm Status Unattempted

A set of atoms in an excited state decays a in general to any of the states with lower energy b into a lower state only when excited by an external electric fie c all together simultaneously into a lower state d to emit photons only when they collide

61 9 Three resistors of resistances 3 2 4 2 and 5 2 are combined in parallel This combination is connected to a battery of emf 12 V and negligible internal resistance current through each resistor in ampere is a 4 3 2 4 b 8 7 3 4 d 5 5 8 2 c 2 5 1 8

D B Match the columns Column A 1 Contact force 2 Stretching a rubber band 3 Non contact force 4 Friction 5 Polishing Column B a Magnetic force b Opposes relative motion c Reduces friction d Muscular force e Force as a pull SHORT AND PRECISE A Show the given text in form of the flowcharts 1 Types of forces Give reasons for the following statements 1 Force does not change the mass of the body 2 Types of friction

A spherical shell of radius 10 cm is carrying a ch rge q If the electric potential at distances 5 cm 10 cm and 15 cm from the centre of the spherical shell is V V and Va respectively then 1 V V Va 2 V V V 3 V V V3 4 V V V3

2 T T Time period of thin bar magnet of vibration magnetometer is T If it cuts into two equal parts in then ime period of each part fashions Along or parallel to its length T T 2 T T 2 b Perpendicular to its length 3 T 2 T 4 T 2 T 2

SolveLancer Test Which of the following statement is correct 1 For a non uniform gravitational field centre of gravity coincides with the centre of mass for a body II using Faraday s law we can find the direction of induced current due to changing magnetic field III wave speed depends on its source IV reading of spring balance will be same on earth and on moon for a given body SolveLancer Test a i iii iv b ii iii c i ii iii iv d none

The following four wires are made of same material Which of these will have the largest extension when the same tension is applied NEET 2013 a Length 50 cm diameter 0 5 mm b Length 100 cm diameter 1mm c Length 200 cm diameter 2 mm d Length 300 cm diameter 3 mm

Example 14 12 Take A and B input waveforms similar to that in Example 14 11 Sketch the output waveform obtained from AND gate Solution Hence Y 0 A 0 B 0 A 1 B 0 Hence Y 0 A 1 B 1 Hence Y 1 Hence Y 0 Hence Y 0 A 0 B 1 A 0 B 0 A 1 B 0 Hence Y 0 Hence Y 0 A 0 B 1 For t t Based on the above the output waveform for AND gate can be drawn as given below For tst For t to ti For t to ti For t to t For t to ti For to to toi ta

2 The dimensional formula of thermal conductivity is A and that of thermal resistance is B Then dimensional formula of length will be 1 AB 3 A B Two identical 2 AB BA 4 conducting rods are fi

16 If earth suddenly stop rotating then the weight of an object of mass m at equator will o is angular speed of earth and R is its radius 1 Decrease by mo 2R 2 Increase by mo 2R 3 Decrease by moR 2 4 Increase by moR 2

7 Velocity of a body moving along a straight line with uniform acceleration a reduces by of its initial velocit 3 4 in time to The total time of motion of the body till its velocity becomes zero is

In a series resonant R L C circuit if L is increased by 25 and C is decreased by 20 then the resonant frequency will 1 2 4 orrect Answer 3 our Answer 4 atus incorrect Increases by 10 Decreases by 10 Remain unchanged Increases by 2 5

TEMPERATURE DEPENDENCE OF RESISTIVITY 28 The resistance of a heating element is 99 2 at room temperature What is the temperature of the element if the resistance fs found to be 116 52 T Temperature coefficient of the material of the resistor is 1 7 x 10 C 1 a 999 9 C r 1020 2 C b 1005 3 C d 1037 1 C 27 35

8 A man carries a load on his head through a distance of 5 m The minimum amount of work is done when he 1 Moves it over an inclined plane 2 Moves it over a horizontal surface 3 Lifts it vertically upwards 4 first on inclined plane and then upwards

4 If magnitude of average speed and average velocity over a time interval are same then 1 The particle must move with zero acceleration 2 The particle must move with non zero acceleration 3 The particle must be at rest 4 The particle must move in a straight line without turning back

3 A particle moves along x axis with speed 6 m s for the first half distance of a journey and the second half distance with a speed 3 m s The average speed in the total journey is 1 5 m s 2 4 5 m s 3 4 m s 4 2 m s

39 A heater coil is rated 100 W 200 V It is cut into two idential parts Both parts are connected together in parallel to the same source of 200 V The energy liberated per second in the new combination is a 100 b 2001 c 300J d 400

Example 14 11 Justify the output waveform Y of the OR gate for the following inputs A and B given in Fig 14 37 Solution Note the following At t t A 0 B 0 For t to t A 1 B 0 For t to ti A 1 B 1 For t to t A For t to t For t to t For t t Therefore the Hence Y 0 Hence Y 1 Hence Y 1 Hence Y 1 Hence Y 0 Hence Y 1 A 0 B 1 Hence Y 1 waveform Y will be as shown in the Fig 14 37 t t A 0 B 1 0 B 0 A 1 B 0 A Input B Y

An airplane needs to head due north but there is a wind blowing from the northeast at 50 km hr The plane flies at an airspeed of 650 km hr To end up due north the pilot will need to fly the plane degrees east of north

A 6 kg cube has 15 cm length sides The cube is completely submerged in a tank of salt water and placed on to a vertical spring that is attached to the bottom of the tank The spring compresses a distance of 7 cm The density of salt water is 1025 kg m a Calculate the spring constant of the spring b Calculate how deep the top of the spring should be so that the total pressure on it is 130 kPa

Q7 Two forces 3N and 2 N are at an angle q such that the resultant is R The first force is now increased to 6N and the resultant become 2R The value of q is HP PMT 2000 a 30 b 60 c 90 d 120

ELECTRIC CURRENT 1 Ten million electrons pass from point P to point Q in one micro second The current and its direction is l a 1 6 x 10 A from point P to point Q b 3 2 x 10 A from point P to point Q c 1 6 x 10A from point Q to point P 2x 10 12 A from point Q to point P 7 TH ci a E c c

1 20 points Given the two vectors A and B where vector A 22 2 k and that vector B 2 3 2k please find the following a 4 points The magnitudes of the two vectors A and B b 4 points The unit vector in the direction of A c 4 points The dot product of A B d 4 points The cross product of A x B

x 10 Vm 100 In a Van de Graaff type generator a spherical me shell is to be 15 x 10 V electrode The dielectr strength of the gas surrounding the electrodes 5x 10 Vm The minimum radius of the spheric shell required is a Im c 1 5 m b 2 m d 3 m c d 3 An chan a

Exercise 5 Fill in the blanks with the correct forms of the verbs in brackets Use the simple past past continuous past perfect or present tense 1 Saroja 2 Anil came at 10 30 You 3 Gopi 4 We get start 5 The boy 5 He feel play her hand while she very asleep while he to the cinema late so the film while he tired because he the dinner burn cook to bed by that time go the magazine fall read already fall run football for two hours

Tollowing cases i x 3 5 The position of a particle as a function of time is given by x 61 0 5 What is its velocity at 1s 5 The position of a stone dropped from rest from a cliff i

on of ng to and t to be uring 9 d all of these The voltage V and current I graphs for a conductor at two different temperatures and T are shown in the figure The relation between T and T is o a T T b T T c T T d T T

38 93 What is the energy stored in the capacitor betwe Terminals a and of the network shown in th figure Capacitance of each capacitance C 1uF a 12 5 l c 25 l 94 Consider a par b Zero d 50 l lates 20cm

a 125 l c 25 pl b Zero d 50 l 94 Consider a parallel plate capacitor with plates 20 m by 20 cm a separated by 2mm The dielectric constant of the material between the plates is 5 The plates are connected to a voltage source of 500 V The energy density of the field between the plates will be close to a 2 65 1 m c 1 38 1 m b 1 95 1 m d 0 69 1 m 98

c 6 2 d 2 25 x 10 electrons s A current in a wire is given by the equation 1 2 3t 1 the charge through cross section of wire in time interval t 3 sto t 5 sis b 43 34 C a 32 33 C c 45 5 C d 42 C 9 c d Th gra dit T

16 A charged particle having drift velocity of 7 5 x 10 ms in electric field of 3 x 10 mobility is m a 6 5 x 10 m b 25 x 10 m Vs c 2 5 x 10 m Vs d 6 5 x 10 m Vs 22

d 1 3 17 A resistor is marked with the rings coloured brown black green and gold The resistance in ohm is a 3 5 x 10 5 6 8 x 10 5 b 1 10 x 10 10 d 1 x 10 5 DEPENDENCE OF RESISTIVITY resistances a 1 2 b 2 1 c 1 1 34

A particle of mass 2 gm and charge 1 C is held at a distance of 1m from a fixed charge of 1 mC If the particle is released it will be repelled The speed of the particle when it is at a distance of 10m from the fixed charge is Question Type Single Correct Type 1 2 3 4 100 m s 90 m s 60 m s 45 m s

20 A particle performs SHM in a straight line In the first second starting from rest it travels a distance a and in the next second it travels a distance b in the same direction The amplitude of the SHM is a a b b 2a b 3 d None of these c 2a 3a b

3 Three point charges of 2 C 3 C and 3 C are kept at the vertices A B and C respectively of an equilateral triangle of side 20 cm as shown in fig What should be the sign and magnitude of charge to be placed at the mid point M of side BC so that 3 C charge at A remains in equilibrium CRSE Delhi 20051 M B20 cm C

14 9 4 Transistor as an Amplifier CE Configuration To operate the transistor as an amplifier it is necessary to fix its operating point somewhere in the middle of its active region If we fix the value of V corresponding to a point in the middle of the linear part of the transfer curve then the de base current I would be constant and corresponding Vec 1 R collector current I will also be constant The de voltage V would also remain constant The operating values of Vand determine the operating point of the amplifier CE If a small sinusoidal voltage with amplitude is superposed on the de base bias by connecting the source of that signal in series with the BB Supply then the base current will have sinusoidal variations superimposed on the value of n As a consequence the collector current V also will have sinusoidal variations superimposed on the value of Ic producing in turn corresponding change in the value of Vo We can measure the ac variations across the input and output terminals by blocking the de voltages by large capacitors E Re Vcc RE 14 32 A simple circuit of a CE transistor amplifier Vo In the discription of the amplifier given above we have not considered any ac signal In general amplifiers are used to amplify alternating signals Now let us superimpose an ac input signalu to be amplified on the bias V de as shown in Fig 14 32 The BB output is taken between the collector and

mndenser system 99 In case of a Van de Graaff generator the breakdow field of air is a 2x 10 V m c 2 x 10 V m b 3 x 10 V mi d 3x 10 Vm 100 In a Van de Graaff type generator a spherical shell is to be 15 x 10 Yala 2 b c

The negatively and uniformly charged nonconducting disc as shown in the figure is rotated clockwis with great angular speed The direction of the magnetic field at point A in the plane of the disc is A into the page B out of the page A C up the page D down the page

Lower end of a uniform inextensible rope of mass 2 kg and leng attached to a block of mass 7 5 kg placed on a horizontal floor Coefficient of friction between the block and the floor is 0 5 The upper end of the rope is held 2 m above the lower end so that the tangent at the lower end remains horizontal as shown in the figure In this situation the block stays standstill on the floor Acceleration due to gravity is 10 m s 5 The upper end must be pulled at an angle that is closest to a 60 above the horizontal c 45 above the horizontal b 53 above the horizontal d Insufficient information 2 m

24 Which of the following is not true about electric charge 1 Charge on a body is always integral multiple of certain charge known as charge of electron 2 Charge is a scalar quantity 3 Net charge on an isolated system is always conserved 4 Charge can be converted into energy and energy can be converted into charge

43 Light coming from a discharge tube filled with hydrogen falls on the cathode of the photoelectric cell The work function of the surface of cathode is 4eV Which one of the following values of the anode voltage in volts with respect to the cathode will likely to make the photo current zero a 4 c 8 b 6 d 10

SolveLancer Test A long thin solenoid has 600 turns per metre and radius 2 4 cm The current in the solenoid is increasing at a uniform rate The induced electric field at a point near the centre of the solenoid and 6 5 cm from the axis is 6 x 10 6 dl dt The value ofis SolveLancer Test a 2 67 A s b 3 19 A s c 1 797 A s d 6 66 A s m

1 t 6 s 4 The particle moves with a constant velocity A particle moves along x axis in such a way tha its x co ordinate varies with time according to the equation x 4 2t t2 The speed of the partic will vary with time as V 2722 v2t 3 V K O O 2 t 2 sto O 1810 6163 to be a vd V in noi 4 O t r 8 Pusa Road New Delhi 110005 Ph 011 47623

A field is 80m long and 50m broad In one corner of the field a pit which is 10m long 7 5 m broad and 8m deep has been dug out The earth taken out of it is evenly spread over the remaining part of the field Find the rise in the level of the field

36 In a semiconductor diode P side is earthed and N side is put at potential of 2 V the diode shall

A projectile of mass m is thrown from the origin O with a speed v0 at an angle e Identify the CORRECT statement Y4 C 0 Angular momentum of the particle about O is always zero Angular momentum of the particle about O increases with time A constant torque acts on the particle about O in the clockwise sense

c only i d i and ii are correct and iii is wrong 38 A molecule of a substance has a permanent electric dipole moment of magnitude 10 cm A mole of this substance is polarised by applying a strong electrostatic field of magnitude 10 V m The direction of field is changed by an angle 60 The heat released by the substance in aligning its dipole along the new direction of the field is a 6 b 31 c 3J alectric dipole of length d 6J 20 cm having ith respect to

ye fe O 2 Two identical metallic spheres each of radius r are fixed with their centres at points d 0 0 and d 0 0 in a homogeneous medium of conductivity o Here d r One of them is maintained at potential V and the other one is grounded as shown in the figure Calculate magnetic flux density at a point that is in the y z plane at a distance R from the origin O Ans Moord d d I Bate R loc disk can rotate about its central vertical axis in a A largo friotic