Physics - in Hindi

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A wire of resistance R is stretched to reduce its diameter to half of its original value, The new resistance is?


प्रतिरोध R का एक तार इस तरह से खींचा कि इसका व्यास उसके प्रारंभिक मान से आधा हो गया है, नया प्रतिरोध होगा?

A)
2R

B)
4R

C)
8R

D)
16R


Correct Answer :

16R


Explanation :

The resistance R of a uniform cylinder of length L, of cross-sectional area A, and made of a material with resistivity ρ

R = ρL/A

New radius = r/2
New area = pi *(r/2)*(r/2)=1/4 of original area

As volume = length * area
new length = 4 * original length

New resistance R1 = ρ 4L/(A/4) = ρ 16*L/A = 16 R

The resistivity of the material depends on?


पदार्थ की प्रतिरोधकता निर्भर करती है?

A)
Length of the wire
/
तार की लंबाई

B)
Diameter of the wire
/
तार के व्यास

C)
Temperature of the wire
/
तार के तापमान पर

D)
Material of the wire
/
तार के पदार्थ पर


Correct Answer :

Material of the wire


Explanation :

The resistance R of a uniform cylinder of length L, of cross-sectional area A, and made of a material with resistivity ρ

Resistance R = ρL/A

The resistivity of a material depends on its nature and the temperature of the conductor, but not on its shape and size. A good conductor has less resistivity, whereas a bad conductor or insulator has high resistivity.
The unit for resistivity is the ohm-metre.

Calculate the energy equivalent of 1g of substance ?


1g पदार्थ के बराबर ऊर्जा की गणना करें?

A)
3*1013 J

B)
6*1013 J

C)
9*1013 J

D)
2*1013 J


Correct Answer :

9*1013 J


Explanation :

As per Einstein's equation E=mc2, where c is the speed of light (~3x108 m/s), m is the mass, and E is amount of energy.
1 g = 0.001 kg

E=0.001kg * (3 * 108 m/s)2
E=0.001 * 9 * 1016 kg*m2/s2
E=9 * 1013 kg*m2/s2

A kg*m2/s2 is a joule that measures energy

The unit of Thermal Conductivity of a material is?


किसी पदार्थ की ऊष्मीय चालकता की इकाई है?

A)

W / mK


B)

W / m2K


C)

Wm / K


D)

W2K / m



Correct Answer :

W / mK


Explanation :

In SI units, thermal conductivity is measured in watts per meter-kelvin (W / mK).

The most common element used in manufacturing of transistor is?


ट्रांजिस्टर के निर्माण में प्रयुक्त सबसे आम तत्व है?

A)

Silicon


B)

Phosphorus


C)

Gallium


D)

Germanium



Correct Answer :

Silicon


Explanation :

Transistor, three-terminal, solid-state electronic device used for amplification and switching.

The first transistors were made from germanium, but now most transistors are made from silicon. Silicon (Si) and germanium (Ge) form similar crystal structures with similar physical properties, but silicon is preferred over germanium because of silicon's superior thermal characteristics.

A larger force on a rotating body results in larger?


घूर्णन करने वाली वस्तु पर लगाये गये एक बड़े बल का परिणाम बड़े .................में होता है?

A)

mass


B)

torque


C)

axis of rotation


D)

centre of mass



Correct Answer :

torque

What is the unit of the physical quantity, magnetic flux density?


भौतिक मात्रा, चुंबकीय प्रवाह घनत्व की इकाई क्या है?

A)

Siemens


B)

Weber


C)

Henry


D)

Tesla



Correct Answer :

Tesla


Explanation :

The tesla (symbol T) is a derived unit of the magnetic induction (also, magnetic flux density) in the International System of Units. One tesla is equal to one weberper square metre.

The unit of relative density is?


सापेक्ष घनत्व की इकाई है?

A)

no unit


B)

kg/m


C)

kg/m3


D)

g/cm3



Correct Answer :

no unit


Explanation :

Relative density of a substance = Density of the substance/Density of water at 4°C As relative density is the ratio of densities, it has no units. (Both the numerator and the denominator have the same units, they cancel each other )

Which of the following modes of heat transfer is faster?


निम्नलिखित में से कौन सा ऊष्मा हस्तांतरण का सबसे तेज विधि है?

A)

Radiation only

/

विकिरण


B)

Conduction only

/

चालन


C)

Convection only

/

संवहन


D)

Both conduction and radiation

/

चालन और विकिरण



Correct Answer :

Radiation only


Explanation :

Radiation is the fastest mode of transfer of heat, because radiation travels at the speed of light, which is very quick. Heat radiation is carried not by moving atoms (as in conduction or convection) but by electromagnetic waves. Radiation is the only way that heat can move through a vacuum.

The slowest mode of transfer of heat is conduction because it takes place from particle to particle.

The force required to produce an acceleration of 4 m/s2 in an object of mass 9 kg is?


9 किलोग्राम द्रव्यमान की वस्तु में 4 m / s2 का त्वरण उत्पन्न करने के लिए आवश्यक बल होगा?

A)

4N


B)

5N


C)

9N


D)

36N



Correct Answer :

36N


Explanation :

By Newton’s second law, F=ma

So, F=9 kg*4 m/s²=36 N

Perspiration(sweat) helps in cooling the body because the ?


पसीना शरीर को ठंडा करने में मदद करता है क्योंकि?

A)

Water evaporates resulting in heat loss of the body


B)

Water evaporates resulting in heat gain of the body


C)

Water sublimes resulting in heat loss of the body


D)

Water condenses resulting in heat gain of the body



Correct Answer :

Water evaporates resulting in heat loss of the body


Explanation :

Sweat (Perspiration) helps cool down by releasing moisture onto skin. sweat evaporates from skin taking a little bit of body heat with it.

Atmospheric pressure at sea level equals ?

A)

1.01 * 107 Pascal


B)

1.01 * 105 Pascal


C)

1.01 * 106 Pascal


D)

1.01 * 109 Pascal



Correct Answer :

1.01 * 105 Pascal


Explanation :

The atmospheric pressure is the weight exerted by the overhead atmosphere on a unit area of surface.

The atmospheric pressure at sea level is given equivalently as P = 1.013*105 Pa = 1013 hPa = 1013 mb = 1 atm = 760 torr.

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