Tag: physics

Questions Related to physics

Which of the following reading is most accurate

physics units and measurement: error analysis accuracy of measurement accuracy and precision accuracy, precision and uncertainty in measurement

  1. 4 cm

  2. 0.004 mm

  3. 40.00 cm

  4. 4.0 m

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Correct Option: D

The mean length of an object is $5\ cm$. Which of the following measurements is most accurate?

physics units and measurement: error analysis accuracy of measurement accuracy and precision accuracy, precision and uncertainty in measurement

  1. $4.9\ cm$

  2. $4.805\ cm$

  3. $5.25\ m$

  4. $5.4\ cm$

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Correct Option: A
Explanation:

According to the problem, the length L = 5 cm 

Let us first check the error in each value by picking options one by one, we get
$\triangle L _1 = 5 -4.9 = 0.1 cm$
$\triangle L _2  = 5 -4.805 = 0.195 cm$
$\triangle L _3 = 5.25 - 5 = 0.25 cm$
$\triangle L _4 = 5.4 -5 = 0.4 cm$
Hence Error $\triangle L _1$ is least.
Hence 4.9 cm is most closer to true value. So 4.9 is more accurate.

When the jaws of a vernier callipers are in contact with each other, the zeroeth division of the vernier scale does not coincide with the zeroeth division. of the main scale but coincides with the second division on it. Discuss the accuracy of the observed readings done with the instrument

physics units and measurement: error analysis accuracy of measurement accuracy and precision accuracy, precision and uncertainty in measurement

  1. Accuracy decreases.

  2. Accuracy increases

  3. no change

  4. cant say

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Correct Option: A

Why are shields made of iron usually provided around precision instruments?

physics units and measurement: error analysis accuracy of measurement accuracy and precision accuracy, precision and uncertainty in measurement

  1. For protection against the effect of moisture in the air

  2. For guiding the instruments against unauthorised handling

  3. For protection against the effect of external magnetic fields

  4. For absorbing heat generated during the functioning of the instruments

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Correct Option: C
Explanation:

 Metals like iron can be used to shield the instruments from external magnetic fields because magnetic fields cannot penetrate metallic surfaces.

Choose the wrong statement.

fluid dynamics option b: engineering physics physics

  1. Viscous force always supports the motion.

  2. A denser fluid always more viscous than a less dense fluid.

  3. Any object cannot have a velocity after a sufficient long time more than its terminal velocity in a given fluid.

  4. If a body is at rest in a fluid then the viscous force on it is zero.

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Correct Option: A
Explanation:

Viscous force is a frictional force which opposes the relative motion between liquid molecules. Terminal velocity is the velocity attained by the particle when net force on it becomes zero the body cannot have more velocity than terminal velocity in respective fluid.

The velocity of falling rain drops attains limited value because of :

fluid dynamics option b: engineering physics physics

  1. surface tension

  2. upthrust due to air

  3. viscous force exerted by air

  4. air current

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Correct Option: C
Explanation:

Gravity does cause things to fall with increasing speed, but as they speed up viscous force by air increases increases. Since according to stokes law $F _r \propto v$.  Eventually the acceleration stops and the raindrop reaches a constant terminal velocity.

Clouds appear to float in air due to:

fluid dynamics option b: engineering physics physics

  1. low density.

  2. air current.

  3. viscosity of air.

  4. buoyancy.

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Correct Option: C
Explanation:

Viscosity of air is responsible for floating of clouds is air

The quality of fountain-pen ink depends largely on:

fluid dynamics option b: engineering physics physics

  1. Surface tension of the liquid

  2. Viscosity of ink

  3. impurities in ink

  4. Density of ink

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Correct Option: B
Explanation:

The quality of fountain-pen ink depends largely on viscosity of ink because as the viscosity of ink is more, it requires hard pressure on the pen to write and as the viscosity of ink is less  we can write smoothly.

Two identical lead shots are dropped at the same time in two glass jars containing water and glycerine. The lead shot dropped in glycerine descends slowly because:

fluid dynamics option b: engineering physics physics

  1. Viscous force is more in water than in glycerine

  2. Viscous force is more in glycerine than in water

  3. Surface tension is more in water

  4. Surface tension is more in glycerine

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Correct Option: B
Explanation:

Glycerine viscosity is 950 cP and water viscosity is 0.89 cP. We can see that glycerine has high viscosity. High viscous force of glycerine increases the time of drop of lead shot than in water.

After the storm, the sea water waves subside due to:

fluid dynamics option b: engineering physics physics

  1. Surface tension of sea-water

  2. Disapperance of heavy currents

  3. The viscosity of sea water

  4. Gravitational pull of the storm

Show answer
Correct Option: C
Explanation:

After the storm, the sea water waves subside due to the viscosity of sea water. Since viscosity's main cause is cohesive force which acts in intermolecular particles. So, sea water waves subside due to these cohesive force between water molecules.