12th Class Physics Magnetic Effects of Current / करंट का चुंबकीय प्रभाव Question Bank

done Case Based (MCQs) - Magnetism and Matter Total Questions - 15

• question_answer1)

  Directions (Q. No. 1 to 5):

  Read the following text and answer the following questions on the basis of the same:

  Earth's magnetism: Earth's magnetic field is caused by a dynamo effect. The effect works in the same way as a dynamo light on a bicycle. Magnets in the dynamo start spinning when the bicycle is pedaled, creating an electric current. The electricity is then used to turn on the light. This process also works in reverse. If you have a rotating electric current, it will create a magnetic field. On Earth, flowing of liquid metal in the outer core of the planet generates electric currents. The rotation of Earth on its axis causes these electric currents to form a magnetic field which extends around the planet. The average magnetic field strength in the Earth's outer core was measured to be 25 Gauss, 50 times stronger than the magnetic field at the surface. The magnetic field is extremely important for sustaining life on Earth. Without it, we would be exposed to high amounts of radiation from the Sun and our atmosphere would be free to leak into space. This is likely what happened to the atmosphere on Mars. As Mars doesn't have flowing liquid metal in its core, it doesn't produce the same dynamo effect. This left the planet with a very weak magnetic field, allowing for its atmosphere to be stripped away by solar winds, leaving it uninhabitable. Based upon the study of lava flows throughout the world, it has been proposed that the Earth's magnetic field reverses at an average interval of approximately 300,000 years. However, the last such event occurred some 780,000 years ago.

  Which of the followings is the reason for Earth's magnetism?
  A)
  Rotation of electric current done clear
  B)
  Rotation of Earth done clear
  C)
  Attraction due to other celestial bodies done clear
  D)
  Solar flares done clear
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• question_answer2)
  Electric current in the Earth's body is generated due to:
  A)
  movement of charged particle in the atmosphere. done clear
  B)
  flowing of liquid metal in the outer core. done clear
  C)
  electric discharges during thunderstorm. done clear
  D)
  its revolution round the Sun. done clear
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• question_answer3)
  Which planet has no own magnetic field?
  A)
  Jupiter done clear
  B)
  Neptune done clear
  C)
  Mars done clear
  D)
  Mercury done clear
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• question_answer4)
  Average magnetic field strength in the Earth's outer core is:
  A)
  5 Gauss done clear
  B)
  25 Gauss done clear
  C)
  500 Gauss done clear
  D)
  Cannot be measured done clear
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• question_answer5)
  Which of the following statements is true?
  A)
  Earth's magnetic field is due to electric current induced in the ionosphere. done clear
  B)
  The average magnetic field strength in the Earth's outer core is equal to the magnetic field at the surface. done clear
  C)
  Earth's magnetic field reverses at an average interval of approximately 3,00,000 years. done clear
  D)
  Angle of dip is same at every point of the surface of Earth, done clear
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• question_answer6)

  Directions (Q. No. 6 to 10):

  Read the following text and answer the  following questions on the basis of the same:

  If we move into space and study the Earth's invisible magnetic field, it wouldn't really look like a bar magnet at all. Earth's magnetic field gets stretched out into a comet-like shape with a tail of magnetism that stretches millions of miles behind the earth, opposite to the Sun. The Sun has a wind of gas that pushes the earth’s field from the left to the right in the picture.

  The core of the Earth is an electromagnet. Although the crust is solid, the core of the Earth is surrounded by a mixture of molten iron and nickle.

  The magnetic field of Earth is caused by currents of electricity that flow in the molten core. These currents are hundreds of miles wide and flow at thousands of miles per hour as the Earth rotates. The powerful magnetic field passes out through the core of the Earth, passes through the crust and enters space. This picture shows the solid inner core region (inner circle) surrounded by a molten outer core (the area between the two circles). The currents flow in the outer core, travel outwards through the rest of the earth's interior.

  If the Earth rotated faster, it would have a stronger magnetic field.

  By the time the field has reached the surface of Earth, it has weakened a lot, but it is still strong enough to keep your compass needles pointed towards one of its poles. All magnets have two poles: a North Pole and a South Pole The magnetic poles of earth are not fixed on the surface, but wander quite a bit. The pole in the Northern Hemisphere seems to be moving northwards in geographic latitude by about 10 kilometres per year by an average..

  Earth's magnetic field has a:
  A)
  shape of the magnetic field of a bar magnet. done clear
  B)
  shape of the magnetic field of a horseshoe magnet. done clear
  C)
  shape of a sphere. done clear
  D)
  None of the above done clear
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• question_answer7)
  Core of the Earth is:
  A)
  an electromagnet.                       done clear
  B)
  a permanent magnet. done clear
  C)
  a unipolar magnet. done clear
  D)
  None of these done clear
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• question_answer8)
  The magnetic poles of Earth are:
  A)
  fixed on the surface done clear
  B)
  wander throughout the Earth's surface done clear
  C)
  wander about 1000 kilometres per year on an average. done clear
  D)
  wander about 10 kilometres per year on an average. done clear
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• question_answer9)
  Earth's magnetic field may increase if:
  A)
  it rotates on its axis faster. done clear
  B)
  its direction of rotation is changed. done clear
  C)
  it revolves round the Sun faster. done clear
  D)
  All of the above            done clear
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• question_answer10)
  The Earth's magnetism is due to:
  A)
  induction of Sun's magnetism. done clear
  B)
  current produced by the movement of molten metals. done clear
  C)
  sea current. done clear
  D)
  revolution of the Earth round the Sun. done clear
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• question_answer11)

  Directions (Q. No. 11 to 15):

  Read the following text and answer the following questions on the basis of the same:

  Super magnet

  The term super magnet is a broad term and encompasses several families of rare-earth magnets that include seventeen elements in the periodic table; namely scandium, yttrium, and the fifteen lanthanides. These elements can be magnetized, but have 'Curie temperatures below room temperature. This means that in their pure form, their magnetism only appears at low temperatures. However, when they form compounds with transition metals such as iron, nickel, cobalt, etc. Curie temperature rises well above room temperature and they can be used effectively at higher temperatures as well. The main advantage they have over conventional magnets is that their greater strength allows for smaller, lighter magnets to be used.

  Super magnets are of two categories:

  (i) Neodymium magnet: These are made from an alloy of neodymium, iron, and boron. This material is currently the strongest known type of permanent magnet. It is typically used in the construction of head actuators in computer hard drives and has many electronic applications, such as electric motors, appliances, and magnetic resonance imaging (MRI).

  (ii) Samarium-cobalt magnet: These are made from an alloy of samarium and cobalt. This second- strongest type of rare Earth magnet is also used in electronic motors, turbo-machinery, and because of its high temperature range tolerance may also have many applications for space travel, such as cryogenics and heat resistant machinery.

  Rare-earth magnets are extremely brittle and also vulnerable to corrosion, so they are usually plated or coated to protect them from breaking, chipping, or crumbling into powder.

  Since super magnets are about 10 times stronger than ordinary magnets, safe distance should be maintained otherwise these may damage mechanical watch, CRT monitor, pacemaker, credit cards, magnetically stored media etc.

  These types of magnets are hazardous for health also. The greater force exerted by rare-earth magnets creates hazards that are not seen with other types of magnet. Magnets larger than a few centimeters are strong enough to cause injuries to body parts pinched between two magnets or a magnet and a metal surface, even causing broken bones.

  Neodymium permanent magnets lose their magnetism 5% every 100 years. So, in the truest sense Neodymium magnets may be considered as a permanent magnet.

  Curie point of pure rare Earth elements is
  A)
  very high. done clear
  B)
  below room temperature. done clear
  C)
  0K. done clear
  D)
  varies from element to element.  done clear
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• question_answer12)
  Neodymium and Samarium are
  A)
  diamagnetic. done clear
  B)
  paramagnetic. done clear
  C)
  ferromagnetic. done clear
  D)
  not magnetic materials. done clear
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• question_answer13)
  Super magnets are about _______ time stronger than ordinary magnets.
  A)
  10 done clear
  B)
  100 done clear
  C)
  1000 done clear
  D)
  10000 done clear
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• question_answer14)
  To raise the Curie point of rare Earth elements.
  A)
  they are coated with gold. done clear
  B)
  compounds are formed with transition metals. done clear
  C)
  they are oxidized. done clear
  D)
  None of the above   done clear
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• question_answer15)
  Neodymium permanent magnets lose their magnetism_...... % every 100 years.
  A)
  50 done clear
  B)
  0.5 done clear
  C)
  10 done clear
  D)
  None of the above done clear
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