Magnetism and Electromagnetism Quiz
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Questions and Answers

What happens when like poles of magnets come together?

  • They attract each other.
  • They repel each other. (correct)
  • They neither attract nor repel each other.
  • They combine to form a stronger pole.

    • Which materials are classified as ferromagnetic?

  • Iron and nickel (correct)
  • Gold and aluminum
  • Copper and silver
  • Zinc and cobalt

    • What effect does heating a permanent magnet have on its magnetism?

  • It converts the magnet into an electromagnet.
  • It enhances the magnetic strength.
  • It has no significant effect.
  • It can demagnetize the magnet. (correct)

    • What is the significance of the Curie temperature in ferromagnetic materials?

    <p>It is the temperature above which materials cannot be magnetized.</p> Signup and view all the answers

    What causes local magnetization in a previously unmagnetized ferromagnetic material when a magnet is near?

    <p>Alignment of atomic poles within domains.</p> Signup and view all the answers

    What are domains in ferromagnetic materials?

    <p>Regions of aligned atomic poles acting like small bar magnets.</p> Signup and view all the answers

    What is the primary magnetic property exhibited by neodymium?

    <p>It is used as a strong and permanent magnet.</p> Signup and view all the answers

    How does the presence of an external magnet affect an unmagnetized ferromagnetic material?

    <p>It induces magnetization, aligning the magnetic domains.</p> Signup and view all the answers

    What would need to be modified if magnetic monopoles were discovered?

    <p>The understanding that magnetism is due to electrical current</p> Signup and view all the answers

    Which of the following statements about magnetic field lines is true?

    <p>They form continuous loops from north to south</p> Signup and view all the answers

    What is the correct relationship used to calculate the magnetic force on a moving charge?

    <p>$F = qvB \sin(\theta)$</p> Signup and view all the answers

    Which factor does NOT affect the magnetic force experienced by a charge?

    <p>The mass of the charge</p> Signup and view all the answers

    What is used to represent the direction of magnetic field lines?

    <p>The direction a compass needle's north end points</p> Signup and view all the answers

    What can be inferred about the unique properties of magnetic field lines?

    <p>They define a unique magnetic field at every point in space</p> Signup and view all the answers

    In the context of magnetism, what does the Right Hand Rule help determine?

    <p>The direction of the magnetic force</p> Signup and view all the answers

    What is the significance of 'areal density' in terms of magnetic field lines?

    <p>It indicates the strength of the magnetic field</p> Signup and view all the answers

    What is the SI unit for magnetic field strength?

    <p>Tesla (T)</p> Signup and view all the answers

    Using the formula $B = \frac{F}{qv \sin \theta}$, which variable does 'B' represent?

    <p>Magnetic field strength</p> Signup and view all the answers

    What direction do you point your thumb to determine the magnetic force on a positive moving charge using RHR-1?

    <p>Direction of velocity</p> Signup and view all the answers

    If a charged particle is moving in a magnetic field, what happens to its speed?

    <p>Remains constant</p> Signup and view all the answers

    What is the relationship between the tesla and gauss?

    <p>1 G = 10^-4 T</p> Signup and view all the answers

    What phenomenon allows protons in giant accelerators to maintain a circular path?

    <p>Magnetic force</p> Signup and view all the answers

    Which statement about cosmic rays is correct?

    <p>They can be forced into spiral paths by the Earth’s magnetic field.</p> Signup and view all the answers

    What is the strength of the Earth’s magnetic field at its surface?

    <p>$5 \times 10^{-5}$ T</p> Signup and view all the answers

    What is the formula used to calculate the Hall emf in a fluid flow?

    <p>$\epsilon = Blv$</p> Signup and view all the answers

    In the context of the Hall effect, what determines the sign of the Hall emf?

    <p>The direction of the magnetic field and velocity</p> Signup and view all the answers

    Given a width of 2.50 m and an average flow velocity of 6.00 m/s, what is the Hall voltage in a magnetic field of $5.00 imes 10^{-5} ext{ T}$?

    <p>$7.50 imes 10^{-4} V$</p> Signup and view all the answers

    What is the role of magnetic force on a current-carrying wire within a magnetic field?

    <p>To convert electric energy to work</p> Signup and view all the answers

    How is torque calculated in systems involving loops of wire in a magnetic field?

    <p>$ au = rF ext{sin} heta$</p> Signup and view all the answers

    What is the value of the magnetic field if a wire carrying 30A current produces a force of 2.3 N at an angle of 60 degrees, with the wire length of 0.12 m?

    <p>$0.75 ext{ T}$</p> Signup and view all the answers

    Which statement accurately describes magnetohydrodynamics (MHD)?

    <p>It relies on electromagnetic forces to pump fluids.</p> Signup and view all the answers

    What does the right-hand rule (RHR-1) indicate about the forces acting on a current-carrying loop in a magnetic field?

    <p>Forces have equal magnitudes and opposite directions, creating torque.</p> Signup and view all the answers

    What is the primary purpose of the coils in a cathode ray tube (CRT)?

    <p>To steer the electron beam to its desired location</p> Signup and view all the answers

    What effect does an externally applied magnetic field have on certain nuclei in MRI?

    <p>It aligns the nuclei into different energy states</p> Signup and view all the answers

    Which of the following describes the phenomenon used in MRI?

    <p>Nuclear Magnetic Resonance (NMR)</p> Signup and view all the answers

    What frequency characteristic is significant in nuclear magnetic resonance?

    <p>Frequency depends on the chemical environment and magnet strength</p> Signup and view all the answers

    Who were the pioneers in formulating Nuclear Magnetic Resonance in 1946?

    <p>F. Bloch and E. Purcell</p> Signup and view all the answers

    What is the typical strength of the magnetic field created by the superconducting magnet in an MRI unit?

    <p>1 to 2 T</p> Signup and view all the answers

    What major scientific contribution did P. Lauterbur and P. Mansfield receive the Nobel Prize for?

    <p>Applications of magnetic resonance imaging (MRI)</p> Signup and view all the answers

    Which of the following is NOT a characteristic of MRI?

    <p>Produces images in only black and white</p> Signup and view all the answers

    Study Notes

    Magnetism

    • All magnets have two poles: a north magnetic pole and a south magnetic pole.
    • Like poles repel and unlike poles attract.
    • It is impossible to separate north and south poles in magnets.
    • Ferromagnetic materials strongly respond to magnets and can be magnetized.
    • Ferromagnetic materials include iron, cobalt, nickel, gadolinium, and alloys of rare earth elements like neodymium.
    • When a magnet is brought near an unmagnetized ferromagnetic material, it causes local magnetization with unlike poles closest.
    • Domains within the material act like small bar magnets.
    • Domains are small and randomly oriented in an unmagnetized object.
    • Permanent magnets can be demagnetized by hard blows or heating in the absence of another magnet.
    • A ferromagnetic material loses its magnetic properties above the Curie temperature.
    • Curie temperature for iron is 1043 K (770°C).

    Electromagnets

    • Electrical currents cause magnetic effects.
    • Magnetic monopoles (isolated north or south magnetic poles) are not observed.

    Magnetic Fields and Magnetic Field Lines

    • Magnetic fields represent magnetic forces.
    • The direction of magnetic field lines is defined as the direction in which the north end of a compass needle points.
    • Magnetic field is often called the B-field.
    • Magnetic field line properties:
      • The direction of the magnetic field is tangent to the field line at any point.
      • Field strength is proportional to the closeness of the lines.
      • Magnetic field lines never cross.
      • Magnetic field lines are continuous, forming closed loops without beginning or end. They go from the north pole to the south pole.

    Magnetic Field Strength

    • Magnetic fields exert forces on moving charges.
    • The magnitude of the magnetic force (F) on a charge moving at a speed (v) in a magnetic field of strength (B) is given by: F = qvB sin θ , where θ is the angle between the directions of v and B.
    • This force is also known as the Lorentz force.
    • The SI unit for magnetic field strength is the tesla (T).
    • 1T = 1 N/(C.m/s) = 1 N/(A.m)
    • Another unit is the gauss (G), where 1G = 10-4 T.
    • The strongest permanent magnets have fields near 2T, superconducting electromagnets may attain 10 T or more.
    • The Earth’s magnetic field on its surface is about 5 x 10-5 T or 0.5G.

    Right Hand Rule 1

    • To determine the direction of the magnetic force on a positive moving charge, point the thumb of the right hand in the direction of v, the fingers in the direction of B, and a perpendicular to the palm points in the direction of F.
    • The force on a negative charge is in the opposite direction to that on a positive charge.

    Force on a Moving Charge in a Magnetic Field

    • Magnetic force can cause a charged particle to move in a circular or spiral path.
    • Cosmic rays are energetic charged particles in space that can be forced into spiral paths by the Earth's magnetic field.
    • Protons in giant accelerators are kept in a circular path by magnetic force.
    • Magnetic force is always perpendicular to velocity, so it does no work on the charged particle, and the particle's kinetic energy and speed remain constant.

    Hall Effect

    • The Hall effect occurs when a magnetic field is applied perpendicular to the flow of charge in a conductor, resulting in a voltage difference across the conductor (Hall voltage).
    • The Hall effect can be used to measure the speed of fluids.

    Magnetic Force on a Current-Carrying Conductor

    • The magnetic force on charges moving in a conductor is transmitted to the conductor itself.
    • The force on a current-carrying wire in a magnetic field is: F = IlB sin θ, where I is the current, l is the length of the wire, B is the magnetic field strength, and θ is the angle between the wire and the magnetic field.
    • Magnetic force on current-carrying conductors can convert electric energy to work.
    • Magnetohydrodynamics (MHD) is a technique that uses magnetic force to pump fluids without moving mechanical parts.

    Torque on a Current Loop: Motors and Meters

    • Motors use magnetic force on current-carrying wires to rotate a shaft.
    • Motors have loops of wire in a magnetic field.
    • When current passes through the loops, the magnetic field exerts torque on the loops.
    • Torque is defined as 𝜏 = 𝑟𝐹𝑠𝑖𝑛𝜃, where r is the distance from the pivot the force is applied, and θ is the angle between r and F.
    • Cathode ray tubes (CRTs) use magnetic coils to steer electron beams, for example, in TVs and computer monitors.

    Magnetic Resonance Imaging (MRI)

    • MRI is a medical imaging tool based on nuclear magnetic resonance (NMR).
    • NMR involves the interaction of an externally applied magnetic field with nuclei of atoms, particularly hydrogen (protons).
    • Each nucleus has a small magnetic field.
    • When placed in an external magnetic field, these nuclei experience a torque that aligns them into one of two energy states, depending on their spin.
    • Radio frequency signals can be used to "flip" the orientation of these small magnets, causing transitions between energy states.
    • The specific frequency of radio waves absorbed and reemitted depends on the type of nucleus, chemical environment, and external magnetic field strength.
    • MRI units use superconducting magnets to create a magnetic field, typically between 1 and 2T.
    • MRI images provide detailed information about structures and organ functions.

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    Chapter 22: Magnetism PDF

    Description

    Test your knowledge on the fundamentals of magnetism and electromagnetism. This quiz covers concepts such as magnetic poles, ferromagnetic materials, and the effects of electrical currents on magnetic fields. Perfect for students studying physics.

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