## WBJEE 2014 | Physics

- Total No of Questions - 50
- Time Limit - 50 mins
- No negative marking

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Question 1 |

In a noiseless transformer an alternating current of 2 A is flowing in the primary coil. The no of turns on the primary and the secondary coils are 100 and 200 respectively. The value of the current in the secondary coil is :

A | 0.08 A |

B | 0.4 A |

C | 5 A |

D | 10 A |

Question 2 |

A luminous object is placed 20 cm from surface of a convex mirror and a plane mirror is set, so that virtual images formed in two mirrors coincide. If the plane mirror is at a distance of 12 cm from object, then focal length of convex mirror is :

A | 5 cm |

B | 10 cm |

C | 20 cm |

D | 40 cm |

Question 3 |

The magnitude of resultant of two equal forces ia equal to either of two forces. Th angle between forces is :

A | pi/3 |

B | 2pi/3 |

C | pi/2 |

D | 3pi/4 |

Question 4 |

A body is moving in a vertical circle of radius r such that the string is just taut at its highest point. The speed of the particle when the string is horizontal is :

A | √gr |

B | √2gr |

C | √3gr |

D | √5gr |

Question 5 |

A particle projected vertically upwards attains max height H. if the ratio of the times to attain a height h(h

A | 4h=3H |

B | 3h=4H |

C | 3h=H |

D | 4h=H |

Question 6 |

A proton and an α-particle, accelerated through the same potential difference, enter a region of uniform magnetic field normally. If the radius of the proton orbit is 10 cm, the n radius of α orbit is :

A | 10 cm |

B | 10√2 cm |

C | 20 cm |

D | 5√2 cm |

Question 7 |

A scooter of mass 120 kg is moving with a uniform velocity of 108 km/h. The force require to stop the vehicle in 10s is :

A | 360 N |

B | 720 N |

C | 180 N |

D | 120 × 10.8 N |

Question 8 |

The min distance of a reflector to hear the echo of monosyllabic sound is : (the speed of sound is 330 m/s)

A | 16.5 m |

B | 33 m |

C | 165 m |

D | 330 m |

Question 9 |

A solid sphere of mass 2kg rolls up a 30° incline with a initial speed 10 m/s. The max height reached by the sphere is :(g = 10 m/s²)

A | 3.5 m |

B | 7.0 m |

C | 10.56 m |

D | 14.0 m |

Question 10 |

A certain force gives a 2 kg object an acceleration of 0.5 m/

^{2}. What acceleration would the same force give to a 10 kg object ?A | 0.1 m/s ^{2} |

B | 0.2 m/s ^{2} |

C | 0.5 m/s ^{2} |

D | 1.0 m/s ^{2} |

Question 11 |

An electron makes transition inside a hydrogen atom. The orbit angular momentum of electron may change by :

A | h |

B | h/3 pi |

C | h/ 2 pi |

D | h/ 4 pi |

Question 12 |

A 2 kg block is dropped from a height from 0.4 m on a spring of force constant k = 1960 N/m. The max compression of the spring is :

A | 0.1 m |

B | 0.2 m |

C | 0.3 m |

D | 0.4 m |

Question 13 |

Some gas at 300 K is enclosed in a container. Now, the container is placed on a fast moving train. While train is in motion, the temperature of gas ;

A | rises above 300 K |

B | falls below 300 K |

C | remains unchanged |

D | becomes unsteady |

Question 14 |

A heat engine absorbs heat at 327°C and exhausts heat at 127°C. The efficiency of engine is η and the max amount of work performed by the engine per kilocalorie of heat input is W. Then :

A | η = 0.38 |

B | η = 0.88 |

C | W = 1596 J |

D | W = 1400 J |

Question 15 |

Potential ata a point at a distance r from the centre of a uniformly charged sphere of radius a(

A | a ^{3} |

B | r |

C | 1/r |

D | 1/a ^{3} |

Question 16 |

A simple pendulum has time period T. The pendulum is completely immersed in a non-vicious liquid whose density is one tenth, of that of the material of the bob. The time period of the pendulum immersed in liquid is :

A | T |

B | √(9/10) T |

C | √(10/9) T |

D | T/10 |

Question 17 |

1 Wb/m

^{2}is equal to :A | 10 ^{4} G |

B | 10 ^{2} G |

C | 10 ^{-2} G |

D | 10 ^{-4} G |

Question 18 |

It is possible to observe total internal reflection when a ray travels from :

A | air into water |

B | air into glass |

C | water into glass |

D | glass into water |

Question 19 |

Two photons of energy 2.5 eV each are incident on a a metal plate whose work function is 4.0 eV, then the no of electrons emitted from the metal surface woll be :

A | one |

B | two |

C | none of these |

D | more than two |

Question 20 |

A bulb is placed between two plane mirrors inclined at an angle of 60°. The no of images formed is :

A | 5 |

B | 6 |

C | 4 |

D | 3 |

Question 21 |

A sonometer wire is vibrating with an amplitude R

_{1}and R_{2}, separated by a large distance are connected by a long wire. The ratio of the charges on them is :A | R _{1}/R_{2} |

B | R _{2}/R_{1} |

C | R _{1}^{2}/R_{2}^{2} |

D | R _{2}^{2}/R_{1}^{2} |

Question 22 |

If we add impurity to a metal those atoms also deflect electron. Therefore :

A | the electrical and thermal conductivity both increases |

B | the electrical and thermal conductivity both decreases |

C | the electrical conductivity increases but thermal conductivity decreases |

D | the electrical conductivity decreases but thermal conductivity increases |

Question 23 |

A simple pendulum with length L and mass of the bob is vibrating with an amplitude a. Then the max tension in the string :

A | mg |

B | mg[1 + (a/L) ^{2}] |

C | mg[1 + a/2L] ^{2} |

D | mg[1 + (a/L)] ^{2} |

Question 24 |

An electric dipole placed i an a uniform electric field will have min potential energy when the dipole moment is inclined to the field at an angle ;

A | pi |

B | pi/2 |

C | zero |

D | 3 pi/2 |

Question 25 |

Two bodies of equal masses are connected by a light inextensible string passing over a smooth frictionless pulley. The amount of mass that should be transferred from one to another, so that both the masses mole 50 m in 5 s is :

A | 30% |

B | 40% |

C | 70% |

D | 50% |

Question 26 |

Energy required to accelerate a car from 10 m/s to 20 m/s compared with that required to accelerate, if from 0 to 10 m/s is :

A | twice |

B | thrice |

C | four times |

D | same |

Question 27 |

To double the covering range of a TV transmitter tower, its height should me made :

A | 2 times |

B | 4 times |

C | √2 times |

D | 8 times |

Question 28 |

The sun subtends an angle of half a degree at the pole of a concave mirror which has a radius of curvature of 15 m. Then the size(diameter) of the image of the sun formed by the concave mirror is :

A | 7.5 cm |

B | 6.55 cm |

C | 3.7 cm |

D | 13.1 cm |

Question 29 |

A thoroidal solenoid with an air core has an average radius of 15 cm, area of cress-section 12 cm

^{2}and 1200 turns. Ignoring the field variation across the cross-section of the toroid the self-inductance of the toroid is:A | 4.6 mH |

B | 6.9 mH |

C | 2.3 mH |

D | 9.2 mH |

Question 30 |

Two plane mirror are placed perpendicular to each other. A ray strikes one mirror and after reflection from the second mirror will be :

A | perpendicular to the original ray |

B | parallel to the original ray |

C | at 45° to the original ray |

D | can be at any angle to the original ray |

Question 31 |

The ratio areas between the electron orbits for the first excited state to the ground state for hydrogen atom is :

A | 2:1 |

B | 4:1 |

C | 8:1 |

D | 16:1 |

Question 32 |

How many times more intense is a 90 dB sound than a 40 dB sound:

A | 2.5 |

B | 5 |

C | 50 |

D | 10 ^{5} |

Question 33 |

In a triode value a change in anode voltage from 200 V to 240 V on a constant grid voltage produces an increase of anode current from 5 mA to 9.6 mA. The AC anode resistance is :

A | 870 Ω |

B | 8700 Ω |

C | 87000 Ω |

D | 870000 Ω |

Question 34 |

A combination of convex and concave lenses has power 4D. If the convex lens has power 5D the focal length of the concave lense will be :

A | 100 cm |

B | - 100 cm |

C | -1 cm |

D | 100/9 cm |

Question 35 |

A solenoid 30 cm is long is made by winding 2000 loops of wire on an iron rod whose cross section is 1.5 mm

^{2}. If the relative permeability of the iron is 6000, what is the self-inductance of the solenoid ?A | 1.5 H |

B | 2.5 H |

C | 3.5 H |

D | 0.5 H |

Question 36 |

If 1 mg U

^{235}is completely annihilated, the energy liberated is:A | 9 × 10 ^{10} J |

B | 9 × 10 ^{19} J |

C | 9 × 10 ^{18} J |

D | 9 × 10 ^{17} J |

Question 37 |

In a shunted ammeter, only 10% of current passes through the galvanometer of resistance G. The resistance of the shunt is :

A | 9G |

B | 10G |

C | G/9 |

D | G/10 |

Question 38 |

The moment of inertia of the body about an axis is 1.2 kg m

^{2}. Initially the body is at rest. In order to produce a rotational kinetic energy of 1500 J, an angular acceleration of 25 rad/s^{2}must be applied about the axis for the duration of :A | 2 s |

B | 4 s |

C | 8 s |

D | 10 s |

Question 39 |

If X = ε

_{o}lv / t, where ε_{o}is the permittivity of free space, l is light v is potential difference and t is time. The dimension of X are same as that of :A | charge |

B | resistance |

C | voltage |

D | current |

Question 40 |

a bar magnet has coercivity 4×10

^{3}A/m. It is desired to demagnetise by inserting it inside a solenoid 12 cm long and having 60 turns. The current that should be sent through the solenoid is :A | 2 A |

B | 4 A |

C | 6 A |

D | 8 A |

Question 41 |

An electron moving with velocity 2×10

^{7}m/s describes a circle in a magnetic field of strength 2×10^{2}T. The min momentum of the electron may be :×kg m /sA | 6.6 × 10 ^{-20} kg m /s |

B | 3.3 × 10 ^{-20} kg m /s |

C | 3.3 × 10 ^{-48} kg m /s |

D | 6.6 × 10 ^{-48} kg m /s |

Question 42 |

The vol of a bolock of metal changes by 0.12% when heated through 20°C. Then α is :

A | 2.0× 10-5 /°C |

B | 4.0× 10-5 /°C |

C | 6.0× 10-5 /°C |

D | 8.0× 10-5 /°C |

Question 43 |

A copper wire of cross sectional area = 2.0 mm

^{2}, resistivity = 1.7×10^{8}Ωm, carries a current of 1 A. The electric field in the copper wire is :A | 8.5 × 10 ^{-5} V/m |

B | 8.5 × 10 ^{-4} V/m |

C | 8.5 × 10 ^{-3} V/m |

D | 8.5 × 10 ^{-2} V/m |

Question 44 |

A cooking pot should have :

A | high specific heat and low conductivity |

B | high specific heat and high conductivity |

C | low specific heat and low conductivity |

D | low specific heat and high conductivity |

Question 45 |

In some region, the gravitational field is zero. The gravitational potential in this region :

A | may be zero |

B | cannot be zero |

C | must be change |

D | none of the above |

Question 46 |

If Φ is phase difference between current and voltage, the wattless component current is :

A | I cos Φ |

B | I sin Φ |

C | I tan Φ |

D | I cos ^{2} Φ |

Question 47 |

The transfer ratio β of a transistor is 50. The input resistance of the transistor when used in the common emitter mode is 1 k Ω. The peak value of the collector alternating current for an input peak voltage of 0.01 V is:

A | 100 µA |

B | 500 µA |

C | 0.01 µA |

D | 0.25 µA |

Question 48 |

The voltage gain of an amplifier without feedback is 100. If a negative feedback is introduced, with a feedback friction β = 0.1, then the gain of the feedback amplifier is :

A | 9.09 |

B | 10 |

C | 100.1 |

D | 90 |

Question 49 |

Monochromatic light incident on a metal surface emits electrons with kinetic energies from 0 to 2.6 eV. What is the least incident energy, if the tightly bound electron needs 4.2 eV to be removed?

A | 1.6 eV |

B | from 1.6 eV to 4.2 eV |

C | from 4.2 eV to 6.8 eV |

D | more than 6.8 eV |

Question 50 |

The ratio of the adiabatic bulk modulus to the isothermal bulk modulus of a perfect gas is equal to :

A | C _{P} - C_{V} |

B | C _{P}/C_{V} |

C | C _{V}/C_{P} |

D | √C _{P}/C_{V} |

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