Tips and Tricks of The Day

Record Limit : 

    2019-03-19 11:22:50.0
Ex: The angle of dip at a place is 60°. At this place the total intensity of earth's magnetic field is 0.64 units. The horizontal intensity of earth's magnetic field at this place is
A) 1.28 units                               
B) 0.64 units
C) 0.16 units                               
D) 0.32 units
Trick: BH = Bcosφ = 0.64 × cos60o = 0.64×12 = 0.32units
    2019-03-18 11:01:50.0
Ex: The point whose abscissa is equal to its ordinate and which is equidistant from the points (1,0) and (0,3) is
A) (1, 1)
B) (2, 2)
C) (3, 3)
D) (4, 4) 
Let the point be (x, x), so according to the condition (x−1)2 + (x−0)2 = (x−0)2 + (x−3)2  ⇒ −2x+1 = −6x+9 ⇒ x = 2.  
Hence the point is (2, 2).
    2019-03-15 12:30:14.0
Ex: A body A is projected upwards with a velocity of 98m/s. The second body B is projected upwards with the same initial velocity but after 4 sec. Both the bodies will meet after
A) 6 sec   
B) 8 sec
C) 10 sec 
D) 12 sec
Explanation: Let t be the time of flight of the first body after meeting, then (t−4)sec will be the time of flight of the second body. 
Since h1 = h2   
 ∴98t − 1/2gt2 = 98(t−4)−1/2g(t−4)2
t = 12seconds
    2019-03-14 11:52:59.0
Ex: An electric dipole has the magnitude of its charge as q and its dipole moment is p. It is placed in a uniform electric field E. If its dipole moment is along the direction of the field, the force on it and its potential energy are respectively
A) 2q⋅E and minimum                                      
B) q⋅E and p⋅E
C) Zero and minimum            
D) q⋅E and maximum
Explanation: In the given condition angle between p⃗  and E⃗  is zero. Hence potential energy U = −pEcos0 = −pE= min. Also in uniform electric field 
Fnet = 0.
    2019-03-13 11:56:47.0
Ex: In chemical reaction A⇌B, the system will be known in equilibrium when
A) A completely changes to B
B) 50% of A changes to B
C) The rate of change of A to B and B to A on both the sides are same
D) Only 10% of A changes to B
Explanation: When rate of forward reaction is equal to rate of backward reaction the reaction is said to be in equilibrium.
    2019-03-12 12:19:27.0
Ex: A stone is just released from the window of a train moving along a horizontal straight track. The stone will hit the ground following        
A) Straight path
B) Circular path
C) Parabolic path
D) Hyperbolic path
Correct answer: C
Explanation: Due to constant velocity along horizontal and vertical downward force of gravity stone will hit the ground following parabolic path.
    2019-03-11 11:40:47.0
Ex: If two waves of same frequency and same amplitude respectively, on superimposition produced a resultant disturbance of the same amplitude, the waves differ in phase by                             
A) p    
B) 2π/3
C) π/2                                
D) Zero 
Correct answer: B
Explanation: A2 = a2 = a2 + a2 + 2a2cosθ ⇒ cosθ = −12 ⇒ θ = 2π / 3
    2019-03-08 11:42:03.0
Ex: Which of the following is logically equivalent to  ~( ~p⇒q)
A) p∧q 
B) p∧ ~q
C) ~p∧q
D) ~p ∧ ~q
Correct answer: D
Explanation: Since  ~(p⇒q) ≡ p ∧ ~q   ~( ~p⇒q)=  ~p ∧ ~q
    2019-03-07 12:34:29.0
Ex: Two sources of waves are called coherent if
A) Both have the same amplitude of vibrations
B) Both produce waves of the same wavelength
C) Both produce waves of the same wavelength having constant phase difference
D) Both produce waves having the same velocity
Correct answer: C
Explanation: Two coherent source must have a constant phase difference otherwise they can not produce interference.
    2019-03-06 10:45:38.0
Ex: In a solid lattice the cation has left a lattice site and is located at an interstitial position, the lattice defect is
A) Interstitial defect            
B) Valency defect
C) Frenkel defect 
D) Schottky defect
Correct answer: C
Explanation:  When cation shifts from lattice to interstitial site, the defect is called Frenkel defect.