Tag: introduction to magnetic field and magnetic flux

Quizzes (0) Questions (23)

Questions Related to introduction to magnetic field and magnetic flux

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

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

  1. geographic north

  2. the centre of earth

  3. geographic south

  4. Both (A) and (C)
Reveal answer Fill a bubble to check yourself
C Correct answer
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.
Multiple choice physics properties of a magnetic field earth - a gigantic magnet magnetic field of earth introduction to magnetic field and magnetic flux

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

  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.
Reveal answer Fill a bubble to check yourself
B,D Correct answer
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.

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

The magnetic field of earth is due to :

  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.
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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.

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  1. $\sqrt (6/5)$

  2. $\sqrt (5/6)$

  3. 1

  4. $\sqrt (7/6)$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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

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

The value of g decreases inside the surface of Earth because

  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
Reveal answer Fill a bubble to check yourself
B,C Correct answer
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.

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

The actual north magnetic pole of earth

  1. Is situated near the geographic south pole.

  2. Is north pole of the magnetic substance of the earth's core.

  3. Attracts the $N$ pole of the compass needle.

  4. Both $(1)$ and $(2)$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The reason for the magnetic field of the earth is the magnetic substance in the earth’s core. 

So the pole of the earth is the pole of the magnetic substance in the earth’s core.

The actual north magnetic pole of earth is situated near the geographic south pole because the unlike poles attract each other.

 

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

Atoms or molecules of liquid or gaseous mate-rial are in rapid motion and are not aligned. Thus,

  1. Fluids can be easily magnetised

  2. Fluids can never be magnetised

  3. Liquid iron rotating about an axis in earth's core is an exception

  4. Liquid iron rotating about an axis in earth's core is difficult to be magnetised
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

As the material gets heated or it is in its liquid or gaseous state, the atoms or molecules are in rapid motion and are not aligned. Thus, fluids are seldom magnetic. An exception is when a magnetic material such as iron is in its liquid state and is continuously rotating around the axis; the atoms can be aligned in one direction, even though they are in liquid rapid motion.

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

When a Magnetic needle is suspended freely, it always aligns itself in the direction of magnetic north and south pole of the earth, the north pole of the needle gets attracted towards the magnetic south pole of the earth and the south gets repelled equally away from it. So two equal and opposite forces acting on the needle should cancel each other which does not happen because the:

  1. Force of attraction and repulsion are equal but not exactly in opposite direction

  2. Force of attraction and repulsion are not exactly equal even though in opposite direction

  3. Force of attraction and repulsion are not equal and not in opposite direction

  4. Force of attraction and repulsion are exactly equal and opposite in direction
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Though two equal and opposite forces are acting on the needles, they don't cancel each other as they act on two different points and they generate torque which later at proper alignment reaches equilibrium such as

$\sum F=0$ and

$\sum M=0$