## WBJEE - PHYSICS

- Number of Questions : 20
- Time : 30 Minutes
- No negative marking.

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Question 1 |

The magnetic field at the point of intersection of diagonals of a square wire loop of side L carrying a current I is

A | μ _{0}I /πL |

B | 2μ _{0}I /πL |

C | √2μ _{0}I /πL |

D | 2√2μ _{0}I /πL |

Question 2 |

If g is the acceleration due to gravity on the surface of the earth, the gain in potential energy of an object of mass m raised from the earth’s surface to a height equal to the radius R of the earth is

A | mg R /4 |

B | mg R/ 2 |

C | mg R |

D | 2mg R |

Question 3 |

A radioactive nucleus of mass number A, initially at rest, emits an α-particle with a speed ν . The recoil speed of the daughter nucleus will be

A | 2ν / A - 4 |

B | 2ν / A + 4 |

C | 4ν / A - 4 |

D | 4ν / A + 4 |

Question 4 |

If a person can throw a stone to maximum height of h metre vertically, then the maximum distance through which it can be thrown horizontally by the same person is

A | h/2 |

B | h |

C | 2h |

D | 3h |

Question 5 |

A stone of relative density K is released from rest on the surface of a lake. If viscous effects are ignored, the stone sinks in water with an acceleration of

A | g(1–K) |

B | g(1+K) |

C | g(1 - 1/k) |

D | g(1 + 1/k) |

Question 6 |

In an inelastic collision an electron excites as hydrogen atom from its ground state to a M-shell state. A second electron collides instantaneously with the excited hydrogen atom in the M-State and ionizes it. At least how much energy the second electron transfers to the atom in the M-state?

A | +3.4 eV |

B | +1.51 eV |

C | –3.4 eV |

D | –1.51 eV |

Question 7 |

A body of mass 6 kg is acted upon by a force which causes a displacement in it given by, x = t

^{2}/ 4 metre where t is the time in second. The work done by the force in 2 seconds isA | 12 J |

B | 9 J |

C | 6 J |

D | 3 J |

Question 8 |

Five equal resistance, each of resistance R, are connected as shown in figure below. A battery of V volt is connected between
A and B. The current flowing in FC will be

A | 3V/R |

B | V/R |

C | V/2R |

D | 2V/R |

Question 9 |

A particle is moving with a constant speed ν in a circle. What is the magnitude of average velocity after half rotation?

A | 2ν |

B | 2 v/π |

C | v/ 2 |

D | v/ 2π |

Question 11 |

If the Earth were to suddenly contract to 1/n th of its present radius without any change in its mass, the duration of the new day will be nearly

A | 24/n hr. |

B | 24 n hr. |

C | 24/n ^{2} hr. |

D | 24n ^{2} hr. |

Question 12 |

A cricket ball of mass 0.25 kg with speed 10 m/s collides with a bat and returns with same speed within 0.01 S. The force acted on bat is

A | 25 N |

B | 50 N |

C | 250 N |

D | 500 N |

Question 13 |

Two cells with the same e.m.f. E and different internal resistances r

_{1}and r_{2}are connected in series to an external resistance R. The value of R so that the potential difference across the first cell be zero isA | √r _{1}r_{2} |

B | r _{1} + r_{2} |

C | r _{1} - r_{2} |

D | r _{1} + r_{2}/2 |

Question 15 |

In the nuclear reaction

^{14}_{7}N + X ->^{14}_{6}C +^{1}_{1}H the X will be?A | ^{0}_{-1}e |

B | ^{1}_{1}H |

C | ^{2}_{1}H |

D | ^{1}_{0}n |

Question 16 |

A | CE |

B | CE R _{1}/ R_{1} + r |

C | CE R _{2}/ R_{2} + r |

D | CE R _{1}/ R_{2} + r |

Question 17 |

A material has Poisson’s ratio 0.50. If a uniform rod of it suffers a longitudinal strain of 2 × 10

^{–3}, then the percentage change in volume isA | 0.6 |

B | 0.4 |

C | 0.2 |

D | Zero |

Question 18 |

A box is moved along a straight line by a machine delivering constant power. The distance moved by the body in time t is proportional to

A | t ^{ 1/2 } |

B | t ^{ 3/4 } |

C | t ^{ 3/2 } |

D | t ^{ 2 } |

Question 19 |

A cubical vessel of height 1 m is full of water. What is the amount of work done in pumping water out of the vessel? (Take g =10 m s

_{–2})A | 1250 J |

B | 5000 J |

C | 1000 J |

D | 2500 J |

Question 20 |

Current through ABC and A'B'C' is I. What is the magnetic field at P? BP = PB' = r (Here C'B' PBC are collinear)

A | B = 1 2I / 4π r |

B | B = μ _{0}/ 4π (2I/ r) |

C | B = μ _{0}/ 4π (I/ r) |

D | Zero |

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