Tag: physics

Questions Related to physics

AN iron rod burried inside earth along direction becomes a magnet

physics properties of a magnetic field earth - a gigantic magnet magnetic field of earth introduction to magnetic field and magnetic flux

  1. N-S

  2. S-N

  3. Both

  4. None

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Correct Option: A
Explanation:

An iron rod buried inside earth along N-S direction becomes a weak magnet. It is only possible when the earth itself behaves like a magnet.

The bulging of earth at the equator and flattening at the poles is due to 

physics properties of a magnetic field earth - a gigantic magnet magnetic field of earth introduction to magnetic field and magnetic flux

  1. Centripetal force

  2. Centrifugal force

  3. Gravitational force

  4. Electrostatic force

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Correct Option: B
Explanation:

The bulging of equator and flattening at poles is due to rotation of earth. The rotation of earth creates a centrifugal force which is pseudo effect counter balancing the inward acting centripetal force. This pseudo effect pushes the earth outward, bugling from earth, and flattening at poles. 

Hence correct answer is option B.

Define angle of declination at a place :

physics properties of a magnetic field earth - a gigantic magnet magnetic field of earth introduction to magnetic field and magnetic flux

  1. angle between the vertical plane and the geographical meridian

  2. angle between the vertical plane and the magnetic meridian

  3. angle between the geographical meridian and the magnetic meridian

  4. angle between the geographical meridian and horizontal plane

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Correct Option: C
Explanation:

The magnetic meridian is an equivalent imaginary line connecting the magnetic south and north poles and can be taken as the magnetic force lines along the surface of the earth. Therefore a compass needle will be parallel to the magnetic meridian.

The angle between the magnetic and the true meridian is the angle of declination, which is relevant for navigating with a compass.

Assertion : Earth's magnetic field does not affect the working of a moving coil galvanometer.
Reason : The earth's magnetic field is quite weak as compared to magnetic field produced in the moving coil galvanometer.

physics properties of a magnetic field earth - a gigantic magnet magnetic field of earth introduction to magnetic field and magnetic flux

  1. If both assertion and reason are true and reason is the correct explanation of assertion.

  2. If both assertion and reason are true and reason is not the correct explanation of assertion.

  3. If assertion is true but reason is false.

  4. If both assertion and reason are false.

Show answer
Correct Option: A
Explanation:

The field magnet used in a moving coil galvanometer is very strong. The earth's magnetic field is quite weak as compared to the magnetic field produced by the field magnet. Practically the coil rotates under the effect of the strong magnetic field due to the earth does not affect the working of the moving coil galvanometer.

The north pole of earth's magnet is near __________.

physics properties of a magnetic field earth - a gigantic magnet magnetic field of earth introduction to magnetic field and magnetic flux

  1. geographic north

  2. the centre of earth

  3. geographic south

  4. Both (A) and (C)

Show answer
Correct Option: C
Explanation:
The opposite poles of two magnets attract.
So, north pole of earth's magnet is near the geographic south. The magnetic field created by the molten core of the earth have a magnetic south pole near the geographic north pole to attract N-pole.
Hence, option : C.

A magnet is placed earth's magnetic field with south pole of the magnet pointing north. At the neutral point :

physics properties of a magnetic field earth - a gigantic magnet magnetic field of earth introduction to magnetic field and magnetic flux

  1. The earth's magnetic field is zero

  2. The fields of the magnet and the earth are equal and in opposite direction.

  3. The magnet's magnetic field is zero.

  4. The net magnetic field is zero.

Show answer
Correct Option: B,D
Explanation:
If the magnet is placed as the north pole, the magnet is aligned with south of earth magnetic field then at a neutral point, that is the point where magnetic forces are equal and opposite thus fields of both are equal and opposite and Net field is zero.

The magnetic field of earth is due to :

physics properties of a magnetic field earth - a gigantic magnet magnetic field of earth introduction to magnetic field and magnetic flux

  1. Magnetic dipole buried at the centre of the earth

  2. Motion and distribution of some material in and outside the earth.

  3. Induction effect of the sun.

  4. Interaction of gamma rays with the crust of the earth.

Show answer
Correct Option: B
Explanation:

The magnetic field of earth is due to motion and distribution of some materials in and outside the earth.
Our planets magnetic field is believed to be generated deep down in earth's core. The Coriolis force, resulting form the earth's spin, also cause swirling whirlpools. The flow of liquid iron generated electric current, which in turn produces magnetic field.
Hence, option : B.

A body of mass 100 kg falls on the earth from infinity. What will be its energy on reaching the earth? Radius of the earth is 6400 km and g = 9.8 $m/s^2$. Air friction is negligible.

physics properties of a magnetic field earth - a gigantic magnet magnetic field of earth introduction to magnetic field and magnetic flux

  1. 6.27 x $10^9$ J

  2. 6.27 x $10^{10}$ J

  3. 6.27 x $10^{12}$ J

  4. 6.27 x $10^7$ J

Show answer
Correct Option: A
Explanation:

$\begin{array}{l} u\widehat { i } +k\widehat { i } ={ u _{ f } }+{ k _{ f } } \ \Rightarrow 0+0=\frac { { -GMm } }{ R } +\frac { 1 }{ 2 } m{ v^{ 2 } } \ \Rightarrow \frac { 1 }{ 2 } m{ v^{ 2 } }=\frac { { GMm } }{ { R\times R } } \times R \ =mgR \ =100\times 9.8\times 6400\times 1000 \ =6272000\times 1000 \ =6.27\times { 10^{ 9 } }J \end{array}$

Hence,
option $(A)$ is correct answer.

A ball 'A' of mass m falls to the surface of the earth from infinity. Another ball 'B' of mass 2m falls to the earth from the height equal to six times radius of the earth then ratio of velocities of 'A' and 'B' on reaching the earth is

physics properties of a magnetic field earth - a gigantic magnet magnetic field of earth introduction to magnetic field and magnetic flux

  1. $\sqrt (6/5)$

  2. $\sqrt (5/6)$

  3. 1

  4. $\sqrt (7/6)$

Show answer
Correct Option: D
Explanation:

$\begin{array}{l} { v _{ A } }=\sqrt { \dfrac { { 2GM } }{ R }  } \left( { escape\, \, velocity } \right)  \ { v _{ B } }=\sqrt { \dfrac { { 2gh } }{ { 1+\frac { h }{ R }  } }  } =\sqrt { \dfrac { { 2gh } }{ 7 }  } \left( { h=6R } \right)  \ { v _{ B } }=\sqrt { \dfrac { { 2gh6R } }{ 7 }  } =\sqrt { \dfrac { { 12GM } }{ { 7R } }  }  \ \dfrac { { { v _{ B } } } }{ { { v _{ A } } } } =\sqrt { \dfrac { { 2GM } }{ h }  } =\sqrt { \dfrac { { 7R } }{ { 12GM } }  } =\sqrt { \dfrac { 7 }{ 6 }  }  \ Hence, \ \dfrac { { { v _{ _{ B } } } } }{ { { v _{ A } } } } =\sqrt { \dfrac { 7 }{ 6 }  }  \ \therefore \, option\, \, D\, \, is\, correct\, \, answer. \end{array}$

The value of g decreases inside the surface of Earth because

physics properties of a magnetic field earth - a gigantic magnet magnetic field of earth introduction to magnetic field and magnetic flux

  1. A force of upward attraction is applied by the shell or earth above

  2. The shell of earth above exerts no net force

  3. The distance from the centre of the Earth decreases

  4. The density of the material at the centre of the Earth very small

Show answer
Correct Option: B,C
Explanation:

for a point inside  there is no nor force of outside shell

also
$F = \dfrac{{GMx}}{{{R^3}}}.m$        inside the surface where $x$ is distance from centre.
$\therefore$ as we go inside the distance from centre decrease
$\therefore$ $\vec g$ decrease 
hence, option $(B)$ and $(C)$ both are correct.