Physics [Unit & Dimensions] Questions for Railway ALP Stage-II Exam : 27th November 2018

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Q1. Which of the following is not a vector quantity?
इनमें से कौन एक उक्त रेखा (वेक्टर क्वांटिटी) नहीं है?
(a) Speed / गति
(b) Velocity / वेग
(c) Torque / टार्क 
(d) Displacement / विस्थापन
Show Answer
Sol. A vector quantity has a direction and a magnitude, while a scalar has only a magnitude, Speed is a scalar quantity.

Q2. The dimensional formula for universal gravitational constant is
सार्वभौमिक गुरुत्वाकर्षण स्थिरता के लिए आयामी सूत्र क्या है?
(a)  [M^(-2)]
(b) [M^(-1) L^3 T^(-2)]
(c) [M^(-1) L^3 T^2]
(d) [ML^2 T^(-2) ]

Show Answer
Sol. According to the newton’s law of gravitation, the force of attraction between two objects of mass m_1 and m_2 can be given as F=(Gm_1 m_2)/r^2 , where  G is the gravitational constant and r is the distance between the objects
∴G=(F×r²)/(m_1×m_2 ), now on putting the dimensional formula of F, r, m_1 and m_2 in the given expression, we can get the dimensional formula for G as
([F]×[r]²)/([m_1 ][m_2])=([MLT^2 ]×[L]²)/([M][M])
=[M^(-1 ) L^3   T^(-2)]

Q3. Decibel  is used to measure the intensity of
डेसिबल का उपयोग किस की तीव्रता को मापने के लिए किया जाता है?
(a) Magnetic field/ चुंबकीय क्षेत्र
(b) Sound/ ध्वनि
(c) Light/ प्रकाश
(d) Heat/ऊष्मा

Show Answer
Sol. The decibel ( dB) is used to measure sound level, but it is also widely used in electronics, signals and communication. The dB is a logarithmic way of dscribing a ratio. The ratio may be power, sound pressure, voltage or intensity or several other things.

Q4. A micron is equal to
एक माइक्रोन किस के बराबर है-
(a) 0.1 mm
(b) 0.01 mm
(c) 0.001 mm
(d) 0.0001 mm

Show Answer
Sol. 1 Microns is equal to 0.001 Millimeters.

Q5   Dimensional formula of latent heat
गुप्त गर्मी का आयामी सूत्र क्या है?
(a) M0L2T-2
(b) MLT-2
(c) ML2T-2
(d) ML2T-2

Show Answer
Sol. Latent heat is given by energy per unit mass. The dimensional formula is [M0L2T–2].

Q6. Therm is the unit of
थर्म किस की इकाई है ?
(a) Power/ शक्ति
(b) Heat/ऊष्मा
(c) Light/प्रकाश
(d) Distance/दूरी

Show Answer
Sol. The Therm (symbol, thm) is a non-SI unit of heat energy equal to100000 British thermal units (Btu). It is approximately the energy equivalent of burning 100 cubic feet (2.83 cubic metres) – often referred to as 1 CCF – of natural gas.

Q7. Knot is measure of
नॉट क्या मापने में इस्तेमाल किया जाता है?
(a) The speed of ship/जहाज की गति
(b) The curvature of spherical objects/ गोलाकार वस्तुओं का वक्रता
(c) Solar radiation/ सौर विकिरण
(d) Intensity of earthquake shock/ भूकंप की तीव्रता
Show Answer
Sol. A knot is one nautical mile per hour (1 knot = 1.15 miles per hour ). The term knot dates from the 17th century, when sailors measured the speed of their ship by using a device called a “common log.” This device was a coil of rope with uniformly spaced knots, attached to a piece of wood shaped like a slice of pie.
Q8. The dimension of which of the following is the same as that of impulse? 
निम्नलिखित में से किस का आयाम आवेग के समान है?
(a) Volume /आयतन
(b) Momentum / संवेग
(c) Torque /टार्क
(d) Change in the rate of momentum / संवेग की दर में बदलाव
Show Answer
Sol. Dimensional formula for impulse and momentum are  same  MLT-1.

Q9. Which among the following is the fundamental quantity? 
निम्नलिखित में से क्या एक मौलिक मात्रा है?
(a) Volume /आयतन
(b) Time /समय
(c) Velocity /वेग
(d) Force /बल
Show Answer
 Sol. Time in physics is defined by its measurement: time is what a clock reads. In classical, non-relativistic physics it is a scalar quantity and, like length, mass, and charge, is usually described as a fundamental quantity.

Q10. The dimensional formula of coefficient of viscosity is
श्यानता के गुणांक का आयामी सूत्र क्या है?
(a) [MLT-1]
(b) [M-1L2T-2]
(c) [ML-1T-1]
(d) None of these/ इनमें से कोई नहीं
Show Answer
 Sol. Coefficient of viscosity is defined as tangential force required to maintain a unit velocity gradient between two parallel layers of liquid of unit area. Mathematically, Coefficient of viscosity (η)= Fr/Av ( where  F= tangential Force, Area, r= distance between the layers, v= velocity.
   viscosity (η)= (MLT-2 x L )/ (L2 x LT-1)
    = (ML2T-2)/L3T-1
     = ML-1T-1.

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