# Q&A - Ask Doubts and Get Answers

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represents change enthalpy  And  represents the change in internal energy. According to First law of thermodynamics, H and E are related as,
Engineering
179 Views   |

Four identical electrical lamps are labelled 1.5V, 0.5A which describes the condition necessary for them to operate at normal brightness. A 12V battery of negligible internal resistance is connected to lamps as shown, then

• Option 1)

The value of R for normal brightness of each lamp is  $\frac{3}{4} \Omega$

• Option 2)

The value of R for normal brightness of each lamp is $\frac{21}{4} \Omega$

• Option 3)

Total power dissipated in circuit when all lamps are normally bright is 24W

• Option 4)

Power dissipated in R is 21W when all lamps are normally bright

V = IR    For normal brightness current through each bulb is 0.5 A Therefore, Total current = 2A Option 1) The value of R for normal brightness of each lamp is   Incorrect Option 2) The value of R for normal brightness of each lamp is Correct Option 3) Total power dissipated in circuit when all lamps are normally bright is 24W Incorrect Option 4) Power dissipated in R is 21W when all lamps...
Engineering
617 Views   |

When the rms voltages VL, VC and VR are  measured respectively across the inductor L, the capacitor C and the resistor R in a series  LCR  circuit  connected  to  an AC source, it is found that the ratio VL : VC : VR = 1 : 2 : 3. If the rms voltage of the AC source is 100 V, then VR is close to :

• Option 1)

50 V

• Option 2)

70 V

• Option 3)

90 V

• Option 4)

100 V

or   Option 1) 50 V Incorrect Option 2) 70 V Incorrect Option 3) 90 V Correct Option 4) 100 V Incorrect
Engineering
126 Views   |

What is the fractional error in g calculated from $T= 2 \pi \sqrt{\frac{l}{g}}$   ? Given the fractional error in T and l are $\pm$x and $\pm$y respectively.

• Option 1)

x+y

• Option 2)

x-y

• Option 3)

2x+y

• Option 4)

2x-y

Option 1) x+y Option 2) x-y   Option 3) 2x+y   Option 4) 2x-y
Engineering
394 Views   |

Three masses m, 2m and 3m are moving in x-y plane with speed 3u, 2u, and u respectively as shown in figure. The three masses collide at the same point at P and stick together. The velocity of resulting mass will be :

• Option 1)

• Option 2)

• Option 3)

• Option 4)

As we learnt in  Law of Consevation of Momentum -               then  - wherein  Independent of frame of reference     Pi = Py Option 1) Incorrect Option 2) Incorrect Option 3) Incorrect Option 4) Correct
Engineering
100 Views   |

A small ball of mass m starts at a point A . with speed vo and moves along a frictionless track AB as shown. The track BC has coefficient of friction . The ball comes to stop at C after travelling a distance L which is :

• Option 1)

• Option 2)

• Option 3)

• Option 4)

As we learnt in Impulse Momentum Theorem - - wherein If   is increased, average force is decreased    Apply convervation of Energy Let a be the acceleration produced because of friction f=MN  =>  Mmg a = Mg     Option 1) This is incorrect option Option 2) This is incorrect option Option 3) This is correct option Option 4) This is incorrect option
Engineering
172 Views   |

Which of the following is not based on the principle of capillarity

• Option 1)

Floating of wood on eater surface

• Option 2)

Ploughing of soil

• Option 3)

Rise of oil in wick of lantern

• Option 4)

Soaking of ink by bloating paper

As we discussed in concept Capillary - If a tube of very narrow bore is dipped in a liquid, the liquid in the capillary either ascends or descends . - wherein A towel soaks water.   Floating of wood on eater surface Option 1) Floating of wood on eater surface Option is correct Option 2) Ploughing of soil Option is incorrect Option 3) Rise of oil in wick of lantern Option is incorrect Option...
Engineering
158 Views   |

When the angle of contact between a solid and a liquid is 90°, then

• Option 1)

Cohesive force > Adhesive force

• Option 2)

Cohesive force < Adhesive force

• Option 3)

Cohesive force = Adhesive force

• Option 4)

Cohesive force >> Adhesive force

As we discussed in concept Cause of viscosity - Cause of viscosity  in liquids is cohesive -   Cohesive force = Adhesive force Option 1) Cohesive force > Adhesive force Option is incorrect Option 2) Cohesive force < Adhesive force Option is incorrect Option 3) Cohesive force = Adhesive force Option is correct Option 4) Cohesive force >> Adhesive force Option is incorrect
Engineering
225 Views   |

When impurities are added to an elastic substance, its elasticity

• Option 1)

Increases

• Option 2)

Decreases

• Option 3)

Becomes zero

• Option 4)

May increase or decrease

As we discussed in concept Elasticity - That body which regain it's original shape and size - wherein i.e. after removal of deforming force   both way increase or decrease Option 1) Increases Option is incorrect Option 2) Decreases Option is incorrect Option 3) Becomes zero   Option is incorrect Option 4) May increase or decrease Option is correct
Engineering
735 Views   |

What is the change in surface energy, when a mercury drop of radius R splits up into 1000 droplets of radius r?

• Option 1)

$8\rho R^{2}T$

• Option 2)

$16 \rho R^{2}T$

• Option 3)

$24 \rho R^{2}T$

• Option 4)

$36 \rho R^{2}T$

As we discussed in concept Surface Energy - It is defined as the amount of work done in increasing the area of the liquid against surface tension. -      where n= 10000 After calculeting we get Option 1) Option is incorrect Option 2) Option is incorrect Option 3) Option is incorrect Option 4) Option is correct
Engineering
392 Views   |

Water rises in a capillary tube to a certain height such that the upward force due to surface tension is balanced by 75 × 10-4 N, forces due to the weight of the liquid. If the surface tension of water is 6 × 10-2 N/m, the inner-circumference of the capillary must be

• Option 1)

$1.25\times10^{-2}m$

• Option 2)

$0.50\times10^{-2}m$

• Option 3)

$6.5\times10^{-2}m$

• Option 4)

$12.5\times10^{-2}m$

As we discussed in concept @14048  Capillary - If a tube of very narrow bore is dipped in a liquid, the liquid in the capillary either ascends or descends . - wherein A towel soaks water.    Total upward force =circumference    Total upward force = weight of the liquid Option 1) Option is incorrect Option 2) Option is incorrect Option 3) Option is correct Option 4)   Option is incorrect
Engineering
879 Views   |

There is no change in the volume of a wire due to change in its length on stretching. The poison’s ration of the material of the wire is

• Option 1)

+ .50

• Option 2)

- 0.50

• Option 3)

0.25

• Option 4)

- 0.25

Strain - Ratio of change in configuration to the original configuration. -     Volume of wire = Volume remain constant Option 1) + .50 Incorrect Option 2) - 0.50 Correct Option 3) 0.25 Incorrect Option 4) - 0.25   Incorrect
Engineering
568 Views   |

There is a hole in the bottom of tank having water. If total pressure at bottom is 3 atm (1 atm = 105N/m2) then the velocity of water flowing from hole is

• Option 1)

10 m/s

• Option 2)

30 m/s

• Option 3)

20 m/s

• Option 4)

none of these

As we discussed in Torricelli's Theorem / Velocity of Efflux - In fluid dynamics relating the speed of fluid flowing out of an orifice.  - wherein    Gauge pressure at bottom= Option 1) 10 m/s Incorrect Option 2) 30 m/s Incorrect Option 3) 20 m/s Correct Option 4) none of these Incorrect
Engineering
440 Views   |

The work done in blowing a soap bubble of radius R is W1 and that to a radius 3R is W2. the ratio of work done is

• Option 1)

1:3

• Option 2)

3:1

• Option 3)

1:9

• Option 4)

9:1

As we discussed in Work Done in Stretching Wire / Elastic P.E. - - wherein L - Length of wire  - increase in length     Option 1) 1:3 Incorrect Option 2) 3:1 Incorrect Option 3) 1:9 Correct Option 4) 9:1 Incorrect
Engineering
545 Views   |

One end of a uniform wire of length L and of weight W is attached rigidly to a point on the roof and a weight W1 is suspended from its lower end. If S is the area of cross-section of the wire, the stress in the wire at a height 3L/4 from its lower end is,

• Option 1)

$\frac{W_{1}}{S}$

• Option 2)

$\left ( W_{1} +\frac{W}{4}\right )S$

• Option 3)

$\left ( W_{1} +\frac{3W}{4}\right )S$

• Option 4)

$\frac{W_{1}+W}{S}$

As discussed in Stress - The internal restoring force per unit area of deformed body. - wherein Due to the forces, the body gets deformed and internal forces appear.   As discussed in @14070  Total force and height 3L/4 from its lower end = weight suspended + weight of 3/4 of the chain Option 1) This solution is incorrect. Option 2) This solution is incorrect. Option 3) This solution is...
Engineering
123 Views   |

In the following fig. is shown the flow of liquid through a horizontal pipe. Three tubes A, B and C are connected to the pipe. The radii of the tubes A, B and C at the junction are respectively 2 cm, 1 cm and 2 cm. It can be said that the

• Option 1)

Height of the liquid in the tube A is maximum

• Option 2)

Height of the liquids in tubes A and B are same

• Option 3)

Height of the liquids in all three tubes are same

• Option 4)

Height of the liquids in tubes A and C are same

As discussed in Capillary - If a tube of very narrow bore is dipped in a liquid, the liquid in the capillary either ascends or descends . - wherein A towel soaks water.   Heights of liquids in tubes A and C are same.  Option 1) Height of the liquid in the tube A is maximum This solution is incorrect Option 2) Height of the liquids in tubes A and B are same This solution is incorrect Option...
Engineering
673 Views   |

An incompressible liquid flows through a horizontal tube as shown in the following fig. Then the velocity v of the fluid is

• Option 1)

3.0 m/s

• Option 2)

1.5 m/s

• Option 3)

1.0 m/s

• Option 4)

none of these

As discussed in Equation of Continuity - The question of continuity is derived from the principle of conservation of mass. -                                          Option 1) 3.0 m/s This solution is incorrect. Option 2) 1.5 m/s This solution is incorrect. Option 3) 1.0 m/s This solution is correct. Option 4) none of these This solution is incorrect.
Engineering
140 Views   |

A stretched wire has a Young’s modulus $\gamma$ and energy density E. The strain in the stretched wire is

• Option 1)

$\sqrt{\frac{2E}{\gamma }}$

• Option 2)

$\frac{2E}{\gamma }$

• Option 3)

$\frac{4E}{\gamma }$

• Option 4)

$\sqrt{\frac{E}{\gamma }}$

As discussed in Stress - The internal restoring force per unit area of deformed body. - wherein Due to the forces, the body gets deformed and internal forces appear.     Stress -   - wherein    Strain in stretched wire Option 1) This solution is correct Option 2) This solution is incorrect Option 3) This solution is incorrect Option 4) This solution is incorrect
Engineering
172 Views   |

A small sphere of mass m is dropped from a great height. After it has fallen 100 m, it has attained its terminal velocity and continues to fall at that speed. The work done by air friction against the sphere during the first 100 m of fall is

• Option 1)

Greater than the work done by air friction in the second 100 m

• Option 2)

Less than the work done by air friction in the second 100 m

• Option 3)

Equal to 100 mg

• Option 4)

Greater than 100 mg

As discussed in Terminal Velocity - When spherical body attains constant velocity in viscous fluid. -   In the first 100 mts body starts from rest and its velocity goes on increasing and after 100 mts it acquires maximum velocity (terminal velocity) i.e. viscous force which is proportional to velocity. Hence work done against air friction in first 100 m is less than the work done in next 100...
Engineering
137 Views   |

A sheet can be made water proof by coating it with a substance that changes the angle of contact

• Option 1)

to  $\frac{\pi}{2}$

• Option 2)

to zero

• Option 3)

from acute to obtuse

• Option 4)

from obtuse to acute

As we discussed in concept Ascent Formula - For  For  For  - wherein meniscus (concave) Rise meniscus (convex) Fall meniscus (Plane) Plane    From acute to obtuse Option 1) to  This option is incorrect. Option 2) to zero This option is incorrect. Option 3) from acute to obtuse This option is correct. Option 4) from obtuse to acute This option is incorrect.
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