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Q:

When an electric bulb breaks , there is an explosive sound. That is due to

A) the chemical reaction between the gases inside the bulb B) the compressed gases inside rushing out suddenly
C) the air outside rushing in to fill the vacuum inside the bulb D) None of these

Answer:   C) the air outside rushing in to fill the vacuum inside the bulb



Explanation:

The inside of the bulb being a vacuum, the outside air rushes in when the bulb is broken. The vibrations of the rushing air molecules produce the sound.

Subject: Physics
Q:

Sound waves cannot travel in

A) Vacuum B) Water
C) Glass D) Hydrogen gas
 
Answer & Explanation Answer: A) Vacuum

Explanation:

A Sound wave needs a medium for propogation. Hence, Sound cannot travel through a vacuum.

A vacuum is an area without any air, like space. So sound cannot travel through space because there is no matter for the vibrations to work in.

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Q:

Resistance of human body in dry condition

A) 10 ohm B) 1000 ohm
C) 10000 ohm D) 100000 ohm
 
Answer & Explanation Answer: D) 100000 ohm

Explanation:

Under dry conditions, the resistance offered by the human body may be as high as 100,000(10^5) Ohms.

 

Depending on the person, a rough value for the internal resistance of the human body is 300-1,000 Ohms. The skin's resistance is much lower if it is wet or burnt/blistered.



There are a lot of factors involved and not every person has the same electrical resistance. For instance, men tend to have lower resistance than women.

Within the body, the tissues with the greatest resistance are bone and fat - nerves and muscle have the least resistance.

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Q:

Q = mc∆T refers to

A) Enthalpy formula B) Heat Transfer formula
C) Specific Heat formula D) Heat of Vaporization
 
Answer & Explanation Answer: C) Specific Heat formula

Explanation:

Q = mc∆T refers to Specific Heat formula.

 

When heat energy is added to a substance, the temperature will change by a certain amount.

The relationship between heat energy and temperature is different for every material, and the specific heat is a value that describes how they relate.

 

Q = mc∆T

 

Q = heat energy (Joules, J)

m = mass of a substance (kg)

c = specific heat (units J/kg∙K)

∆T = change in temperature (Kelvins, K)

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Q:

Acceptable noise level for human ear

A) > 85 db B) = 85 db
C) < 85 db D) None of the above
 
Answer & Explanation Answer: C) < 85 db

Explanation:

Sound intensity or level is measured by a unit called a decibel. An 85 decibel noise level is not a safe standard for the public.

 

Hence, Acceptable noise level for human ear is less than 85 db.

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Q:

Atmospheric pressure exerted on earth is due to

A) gravitational pull B) rotation of earth
C) revolution of earth D) uneven heating of earth
 
Answer & Explanation Answer: A) gravitational pull

Explanation:

The atmospheric pressure at the surface of the Earth is due to gravitational pull of the earth and is about 14.7 psi.

 

That means that the weight of a column of air which has a cross section of 1 square inch and which stretches from the surface of the Earth to space is 14.7 pounds. 

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1 186
Q:

The modulus of elasticity for mild steel is approximately equal to

A) 210 kN/mm2 B) 100 kN/mm2
C) 80 kN/mm2 D) 10 kN/mm2
 
Answer & Explanation Answer: A) 210 kN/mm2

Explanation:

It is useful to have a property of a material that is independent of the size of the sample and can be use to compare its elastic properties with another - this is called the Modulus of Elasticity for the material.

The modulus of elasticity is defined as:

 

Modulus of elasticity = Stress / Strain

 

There are three types of moduli. They are :

(a) the Young Modulus - tensile and compression longitudinal stress

(b) the shear modulus - a shearing stress

(c) the bulk modulus - volume changes of the specimen.

 

mod-compressor1528180544.jpg image

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Q:

What causes brownian motion in colloids?

A) coagulation of particles and the dispersed phase B) erratic flashes of light
C) molecules of the dispersion medium colliding with dispersed phase particles D) All the above
 
Answer & Explanation Answer: C) molecules of the dispersion medium colliding with dispersed phase particles

Explanation:

When their is a colloid in the solution, then it will show the Brownian movement, such as dust particle in the air will show the Brownian movement.

 

Hence, Brownian movement arises due to the impact of the molecules of the dispersion medium with the colloidal particles. It has been postulated that the impact of the molecules of dispersion medium on the colloidal particles are unequal.

 

This leads to the zig-zag (random) motion of the colloidal particles.

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2 171
Q:

Blotting paper absorbs ink due to

A) Capillary action phenomenon B) Diffusion of ink through the blotting
C) Siphon action D) Viscosity of ink
 
Answer & Explanation Answer: A) Capillary action phenomenon

Explanation:

Blotting paper absorbs ink by the process of capillary action. The capillary action is based on the property of surface tension of liquid.

 

All unsized paper will absorb water. Blotting paper is not sized and made bulkier to provide capillary action for faster absorption of liquid.

 

Blotting paper has also been sold as a cosmetic to aid in the removal of skin oils and makeup.

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