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Friday, May 28, 2021

In a vernier calipers, there are 10 divisions on the vernier scale and 1 cm on the main scale is divided in 10 parts. While measuring a length, the zero of the vernier lies just ahead of 1.8 cm mark and 4th division of vernier coincides with a main scale division. The value of length is

  •  In a vernier calipers, there are 10 divisions on the vernier scale and 1 cm on the main scale is divided in 10 parts. While measuring a length, the zero of the vernier lies just ahead of 1.8 cm mark and 4th division of vernier coincides with a main scale division. The value of length is 
    1. 1.804 cm
    2. 1.840 cm
    3. 1.800 cm
    4. None of these 
        Ans.    As we know that the measurement taken by a vernier calipers
                    = reading on main scale just before zero mark of vernier scale 
                       + (number of divisions of vernier scale coinciding with any main scale division
                          x least count of the vernier calipers)
                    
                   Moreover, we know that the least count of any vernier calipers
                    = the value of smallest division of main scale / number of divisions of vernier scale  
                    = (1 cm/10) / 10 (As per given information)
                    = 0.1 cm/10
                    = 0.01 cm
                    Now, the measurement taken by the vernier calipers
                    = 1.8 cm + (4 x 0.01 cm) (As per given information)
                    = 1.8 cm + 0.04 cm
                    = 1.84 cm  
                    Therefore, option 2 that is 1.840 cm is correct.       
                
                         

In an instrument, there are 25 divisions on the vernier scale which coincide with 24th division of the main scale. 1 cm on main scale is divided in 20 equal parts. The least count of the instrument is

  •  In an instrument, there are 25 divisions on the vernier scale which coincide with 24th division of the main scale. 1 cm on main scale is divided in 20 equal parts. The least count of the instrument is 
  1. 0.002 cm
  2. 0.05 cm
  3. 0.001 cm
  4. 0.02 cm 
    Ans. As we know that the least count of a vernier calipers is 
            = the value of smallest division of main scale / number of divisions of vernier scale  
            = (1 cm / 20) / 25
            = (10 mm / 20) / 25
            = 0.5 mm / 25
            = 0.02 mm
            = 0.002 cm
            Therefore, option 1 that is  0.002 cm is correct.

Thursday, May 27, 2021

A body rises vertically up to a height of 125 m and comes back at the point of projection in 5 s. The average speed of the body was

  •  A body rises vertically up to a height of 125 m and comes back at the point of projection in 5 s. The average speed of the body was 
    1. 25 m/s,
    2. 50 m/s,
    3. Zero
    4. None of these
        Ans.    As we know that speed = distance traveled / time taken,
                    Here, as the speed is changing continuously,
                    Average speed = total distance traveled / total time taken
                                            = (125 m + 125 m) / 5 s,
                                            = 250 m / 5 s
                                            = 50 m/s
                    Therefore, average speed is 50 m/s and option 2. 50 m/s is correct.
 

Wednesday, May 26, 2021

On Fahrenheit scale, the boiling point of water is

  • On Fahrenheit  scale, the boiling point of water is 
  1.  100 ˚F
  2.  98.7 ˚F
  3.  212 ˚F
  4.  220 ˚F
Ans. As per the given figure, boiling point of  water is 212 ˚F , therefore option 3. 212 ˚F is correct.

A hydrometer is used to measure the following quantity of liquid

  •  A hydrometer is used to measure the following quantity of liquid
    1. Density
    2. Volume
    3. Relative density
    4. Pressure
        Ans. 

The correct option is 3. Relative density

Convert 1 mm Hg pressure in Pascal. (Density of Hg = 13.6 X 10^6 Kg/m^3 and g = 9.8 m/s^2)

  • Convert 1 mm Hg pressure in Pascal. (Density of Hg = 13.6 X 10^6 Kg/m^3 and g = 9.8 m/s^2)
    1. 133.28 Pa
    2. 133.80 Pa
    3. 133.12 Pa
    4. 132.98 Pa
        Ans. As we know that 760 mm of Hg pressure = 101300 Pa
                1 mm of Hg pressure = 101300/760 = 133.28 Pa,
                Therefore, option 1. 133.28 Pa is correct.

Tuesday, May 25, 2021

A real and enlarged image can be obtained by using

  •  A real and enlarged image can be obtained by using 
    1. Convex mirror
    2. Plane mirror
    3. Concave mirror
    4. Convex and plane mirror                                            
    
Ans.    Please see above  to understand clearly that when object AB is between focal point and centre  
           of curvature, the image A'B' is real and enlarged.
           So, it is clear that correct option is 3. Concave mirror

Monday, May 24, 2021

Two plane mirrors are placed making an angle of 60˚ in between them. For an object placed in between the mirrors, the number of images formed will be

    • Two plane mirrors are placed making an angle of  60˚ in between them. For an object placed in between the mirrors, the number of images formed will be                                                                                                                                                            
  1. 3
  2. 5
  3. 6
  4. Infinite  

Ans. As per above figure and as we know that number of images formed when two plane mirrors are kept at an angle  degrees is: 

i.e., 

The image formed by a plane mirror is

  • The image formed by a plane mirror is   
                                                                       

    1. Erect and diminished
    2. Erect and enlarged
    3. Inverted and of same size
    4. Erect and of same size
Ans.    As we see in our dressing table mirror or in other domestic mirror, our image is always erect                 and of same size, therefore option 4. Erect and of same size is correct.

A man can hear the sound of frequency

  •  A man can hear the sound of frequency

    1. 1 Hz,
    2. 1000 Hz,
    3. 200 Hz,
    4. 5 MHz,
Ans.    As you know that a man can hear the sound of frequency between 20 Hz and 20,000 Hz.
            Moreover, you know the sounds of frequencies less than 20 Hz i.e. sub sonic and more than 20,000             Hz i.e. ultrasonic, man can not hear. Therefore correct option is 2. 1000 Hz.

The foundation of buildings are made wider than the wall

 

  • The foundation of buildings are made wider than the wall
  1. So that the pressure exerted by the building on the ground becomes less
  2. So that constructing the wall is easy
  3. So that the walls look beautiful
  4. None of these
                                         
    Ans.     As you know that pressure = force / area

         Here, when the foundation of buildings are made wider than the wall, pressure on                 ground is less

        Therefore option 1. So that the pressure exerted by the building on the ground                becomes less is true.