Physics - General Knowledge Questions and Answers

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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?

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?

A)
Length of the wire

B)
Diameter of the wire

C)
Temperature of the wire

D)
Material of the wire


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 ?

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?

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?

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?

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?

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?

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?

A)

Radiation only


B)

Conduction only


C)

Convection only


D)

Both conduction and radiation



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?

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 ?

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.

Which among the following is the SI unit of Force?

A)

Mole


B)

Newton


C)

Kelvin


D)

Ampere



Correct Answer :

Newton


Explanation :

Newton is the SI unit of force, symbol N.

Who received the first Nobel Prize in physics?

A)

Hendrik Antoon Lorentz and Pieter Zeeman


B)

Wilhelm Conrad Rontgen


C)

Antoine Henri Becquerel


D)

Pierre Curie and Marie Curie



Correct Answer :

Wilhelm Conrad Rontgen


Explanation :

The first Nobel Prize in Physics was awarded to physicist Wilhelm Röntgen in recognition of the extraordinary services he rendered by the discovery of the remarkable rays (or X-rays).

Work done is said to be zero when an object moves at an angle of ............with respect to the force applied ?

A)

90°


B)

45°


C)


D)

180°



Correct Answer :

90°


Explanation :

when the force applied and the displacement taking place are at right angles(90°) to each other, then we can say that the work done is zero.

The physical quantity corresponding to the rate of change of displacement is..............?

A)

motion


B)

velocity


C)

acceleration


D)

speed



Correct Answer :

velocity


Explanation :

Rate of change of displacement is velocity.

Displacement and velocity are vector quantities. They have direction.

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