Magnetic Flux Density

Magnetic Flux Density MDCAT MCQs with answers

23 past paper MCQs on Magnetic Flux Density, from the Electromagnetism unit of MDCAT Physics. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

Read the notes first Practise the unit as a quiz

1.The source of a magnetic field is: (MDCAT 2022)

  1. an isolated magnetic pole
  2. a static electric charge
  3. a current loop
  4. a stationary magnet only
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Correct answer: (c) a current loop

Moving charge is what makes a magnetic field, and the current loop is its simplest source.

2.Which of the following statements is incorrect for magnetic field lines? (MDCAT 2024)

  1. lines start at the north pole and end at the south pole
  2. lines never touch or cross each other
  3. the lines are curved
  4. the magnetic field is strongest where the lines are farthest apart
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Correct answer: (d) the magnetic field is strongest where the lines are farthest apart

The field is strongest where the lines are closest together, not farthest apart.

3.The unit of magnetic flux density is: (MDCAT 2024)

  1. $\mathrm{Wb\,m^{2}}$
  2. $\mathrm{Wb\,m}$
  3. $\mathrm{Wb\,m^{-2}}$
  4. $\mathrm{Wb}$
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Correct answer: (c) $\mathrm{Wb\,m^{-2}}$

Flux density is flux per unit area, and $1\ \mathrm{Wb\,m^{-2}}=1$ T.

4.A conductor of length \$1\,\mathrm{m}\$ carrying a current of \$1\,\mathrm{A}\$ is placed parallel to a magnetic field of \$1\,\mathrm{gauss}\$. The magnetic force on the conductor is: (UHS MDCAT 2017)

  1. zero
  2. $1\,\mathrm{N}$
  3. $10^{-4}\,\mathrm{N}$
  4. $1\,\mathrm{dyne}$
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Correct answer: (a) zero

$F=BIL\sin\theta$, and the conductor lies along the field, so $\sin0^{\circ}=0$.

5.A current carrying solenoid is cut in the ratio \$1:3\$ and each part is connected independently to the same source of current. If the field of the first part is \$B_A\$ and of the second \$B_B\$, then: (UHS MDCAT 2017)

  1. $B_A=3B_B$
  2. $B_A=B_B/3$
  3. $B_A=B_B$
  4. $B_A=4B_B$
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Correct answer: (c) $B_A=B_B$

$B=\mu_o nI$ depends on the turns per unit length, and cutting a solenoid leaves that unchanged in both pieces.

6.158.Which of the following statement is incorrect for any magnetic field lines? (UHS MDCAT 2024)

  1. Lines start at north pole and ends at south pole
  2. Lines never touch or cross each other
  3. The lines are curved
  4. Magnetic field is strongest when the lines are farthest
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Correct answer: (d) Magnetic field is strongest when the lines are farthest

The field is strongest where the lines are crowded together, not where they are far apart.

7.159.The unit of magnetic flux density is ; (UHS MDCAT 2024)

  1. Wbm-1
  2. Wbm
  3. Wbm-2
  4. Wb
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Correct answer: (c) Wbm-2

Flux density is flux per unit area, that is webers per square metre, or tesla.

8.Which of the following statement is true about the magnetic filed inside a solenoid? (KMU MDCAT 2024)

  1. It is along the axis of the coil
  2. It is circular around the wires
  3. It is strongest at the ends of the solenoid
  4. It is zero when current flows through it
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Correct answer: (a) It is along the axis of the coil

Inside a long solenoid the field is uniform and runs along the axis.

9.Q.162 The source of magnetic field is: (UHS MDCAT 2023)

  1. An isolated magnetic pole
  2. Static electric charge
  3. Nonmagnetic substance
  4. Current loop
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Correct answer: (d) Current loop

A magnetic field is made by moving charge, that is by a current.

10.The dimension of magnetic field strength is same as that of: (NUMS MDCAT 2023)

  1. Magnetic flux
  2. Magnetic induction
  3. Work done
  4. Magnetic force
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Correct answer: (b) Magnetic induction

Magnetic field strength and magnetic induction are the same quantity, measured in tesla.

11.Tesla is unit of ____ per unit area: (PMC MDCAT 2022)

  1. Magnetic field lines
  2. Electric field lines
  3. Optical field lines
  4. Gravitational field lines
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Correct answer: (a) Magnetic field lines

One tesla is one weber of flux through each square metre.

12.If we cut a magnet in half then both magnets are now (PMC MDCAT 2022)

  1. Monopole
  2. Dipole
  3. Quadrupole
  4. magnetsim is lost
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Correct answer: (b) Dipole

A magnet cut in two gives two magnets, each with its own north and south pole.

13.Magnetic field inside a long solenoid is: (PMC MDCAT 2022)

  1. Varying with radial distance
  2. Uniform
  3. Zero
  4. Not enough Information
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Correct answer: (b) Uniform

Inside a long solenoid the field is uniform and along the axis.

14.When a bar magnet is broken from middle, the broken pieces will have: (PMC MDCAT 2022)

  1. North pole only
  2. Sooth pole only
  3. Both south and north poles
  4. Magnetism will be removed
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Correct answer: (c) Both south and north poles

A magnet cut in two gives two magnets, each with its own pair of poles.

15.The study of magnets is called: (PMC MDCAT 2022)

  1. Electromagnetism
  2. Magnetism
  3. Electrostatics
  4. Current electricity
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Correct answer: (b) Magnetism

The study of magnets and their fields is magnetism.

16.If the current in a wire is doubled then magnetic field would be: (PMC MDCAT 2022)

  1. halved
  2. remain same
  3. triple
  4. double
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Correct answer: (d) double

The field of a current is proportional to it, so twice the current gives twice the field.

17.When two magnets come closer such that same poles face each other than field lines: (PMC MDCAT 2022)

  1. Intersect
  2. Repel
  3. Come closer
  4. Nothing will happen
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Correct answer: (b) Repel

Field lines never cross, so like poles brought together push their lines apart.

18.The strength of a magnetic field is called? (PMC Practice 2021)

  1. Strength
  2. Flux
  3. Magnetic flux density
  4. Density
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Correct answer: (c) Magnetic flux density

The strength of a magnetic field is its flux density, measured in tesla.

19.Magnetic field lines created by current carrying wire are? (PMC Practice 2021)

  1. Helical
  2. Elliptical
  3. Hyperbolic
  4. Circular
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Correct answer: (d) Circular

The lines round a straight wire are circles centred on it.

20.Two parallel straight conductors, in which current is flowing in the same direction, attract each other. The cause of it is: (PMC MDCAT 2020)

  1. magnetic force between the two
  2. electric force between the two
  3. potential difference between the two
  4. mutual induction between the two
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Correct answer: (a) magnetic force between the two

Each current sits in the magnetic field of the other, and parallel currents are drawn together.

21.When current are flowing through two long parallel wires in same direction electric field between them is: (PMC MDCAT 2020)

  1. Strong
  2. Weak
  3. Remains constant
  4. Infinite
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Correct answer: (c) Remains constant

The wires carry no net charge, so the electric field between them does not change; it is the magnetic force that draws them together.

22.Two long, parallel conductors which are free to move are arranged 1.0 cm apart. A steady current of 20 A flows in each of the conductors in the same direction. The conductors: (UHS MDCAT 2018)

  1. Remains stationary
  2. Move towards each other
  3. Move away from each other
  4. Move at right angles to each other
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Correct answer: (b) Move towards each other

Parallel currents in the same direction attract one another.

23.A current carrying solenoid is cut into a ratio 1:3 such that both are independently connected with the same source of current. Now if the magnetic field of the first part is “BA” while the second part respectively is “BB” then what is true? (UHS MDCAT 2017)

  1. BA=3BB
  2. BA=(BB)/3
  3. BA=BB
  4. BA=4BB
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Correct answer: (c) BA=BB

$B=\mu_0nI$ depends on the turns per unit length, which cutting does not change.

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