Tag: physics

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Multiple choice how humans hear sound human ear study of sound sound physics

When a sound wave enters the ear, it sets the eardrum into oscillation, which  in turn causes oscillation of 3 tiny bones in the middle ear called ossicles. This oscillation is finally transmitted to the fluid filled in inner portion of the ear termed as inner ear, the motion of the fluid disturbs hair calls within the inner ear which transmit nerve impulses to the brain with information that a sound is present. The three bones present in the middle ear are named as hammer, anvil and stirrup. Out of these the stirrup is the smallest one and this only connects the middle  ear to inner ear as shown in the figure below. The area of stirrup and its extent of connection with the inner ear limits the sensitivity of the human ear. Consider a person's eat whose moving part of the eardrum has an area of about 43 mm$^{2}$ and the area of stirrup is about 3.2 mm$^{2}$. The mass of ossicles is negligible. As a result, force  exerted by sound wave in air on eardrum and ossicles is same as the force exerted by ossicles on the inner ear. Consider a sound wave having maximum pressure fluctuation of $3\times10^{-2}$ Pa from its normal equilibrium pressure value which is wqual to $10^{5}$ Pa. Frequency of sound wave is 1200 Hz. 
Data: Velocity of sound wave in air is  332 m/s. Velocity of sound wave in fluid (present in inner ear) is 1500 m/s. Bulk modulus of air is $1.42\times10^{5}$ Pa. Bulk modulus of fluid is $2.18\times10^{9}$ Pa.


Find the pressure amplitude of given sound wave in the fluid of inner ear. 

  1. 0.03 Pa

  2. 0.04 Pa

  3. 0.3 Pa

  4. 0.4 Pa
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Given :   Area of stirrup        $A _s = 3.2 mm^2     = 3.2\times 10^{-6}$ $m^2$

             
  Area of eardrum     $A = 43  mm^2  = 43 \times 10^{-6} m^2$

  Pressure amplitude at eardrum    $P _o =  3 \times 10^{-2}$  Pa

Force exerted by sound wave in air on eardrum       

$F =  P _o A = 3 \times 10^{-2} \times 43 \times 10^{-6}   = 129 \times 10^{-8}$N

According to question , force exerted on eardrum is equal to force exerted by ossicles on the inner ear.

Let pressure amplitude in the fluid of inner ear be  $p' _o$

$\therefore$    $p' _o  = \dfrac{F}{A _s}  =  \dfrac{129 \times10^{-8}}{3.2 \times 10^{-6}}   = 0.4$ Pa

Multiple choice physics friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it friction: a necessary evil

Why do we sprinkle powder before playing caroms?

  1. To increase friction

  2. To decrease friction

  3. To increase or decrease the friction depending on the type of the game played.

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Powder acts as a lubricant to the surface and reduces friction so that the game can be carried on smooth surface.

Multiple choice physics friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it friction: a necessary evil

To keep machines running smoothly and to avoid wear and tear of machines, the best and the most commonly used lubricant is:

  1. Powder

  2. Sand

  3. Oil

  4. Water
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Oil is the best and the most commonly used lubricant used for keeping machines running smoothly and to avoiding wear and tear of machines as it reduces the friction more effectively.

Multiple choice physics friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it friction: a necessary evil

The force which prevents us from slipping while walking on the road is:

  1. muscular force of our body

  2. gravitational pull by earth

  3. frictional force

  4. balanced forces of nature
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When we push the ground with our feet, the friction provides a forward reaction to our push and sends us forward. Walking on smooth ground is difficult because the frictional force is not great enough to prevent slipping.


Option C is correct.

Multiple choice physics friction advantages and disadvantages of friction merits and demerits of friction and methods to reduce it friction: a necessary evil

In which of the following cases more friction is desirable?

  1. Movement of piston in a cylinder

  2. Braking of a vehicle

  3. Running on a track

  4. All of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Answer is B.

Brakes is a type of automotive brake that slows or stops a vehicle by converting kinetic energy into heat energy, via friction. The heat energy is then dissipated into the atmosphere. 
Hence, braking of a vehicle happens due to friction.