24 past paper MCQs on Force on a Charged Particle in a Magnetic Field, 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.
1.Electric forces change the magnitude and direction of velocity, while magnetic forces change the: (MDCAT 2022)
Correct answer: (b) direction only
The magnetic force is always perpendicular to the velocity, so it does no work and only turns the particle.
2.The magnitude of the magnetic force on a current-carrying conductor in a uniform magnetic field is maximum if the conductor is: (MDCAT 2023)
Correct answer: (a) perpendicular to the magnetic field
$F=BIL\sin\theta$ is greatest when $\theta=90^\circ$.
3.A proton is projected with a uniform velocity \$v\$ along the axis of a current carrying solenoid. Then: (UHS MDCAT 2017)
Correct answer: (d) the proton will continue to move with velocity $v$ along the axis
Inside the solenoid the field is along the axis, so the velocity is parallel to it and $F=qvB\sin0^{\circ}=0$.
4.Magnetic force acting on a charge at rest is: (NUMS MDCAT 2025)
Correct answer: (a) Zero
The force is $qvB\sin\theta$, and a charge at rest has no velocity, so there is no force.
5.An electron is projected along the positive x-axis in a magnetic field lying in xz-plane. The magnetic force on the electron will act along the: (SIBA MDCAT 2025)
Correct answer: (c) y-axis
The force is along $qv\times B$, and with the velocity along x and the field in the xz plane the product lies along y.
6.An electron is moving perpendicular to the magnetic field, which of the following is correct statement about electromagnetic force acting on the electron? (KMU MDCAT 2024)
Correct answer: (c) Force acting is maximum
$F=qvB\sin\theta$ is greatest when the angle is a right angle.
7.For a positive charged particle (q) moving with a velocity (v) in a magnetic Filed of flux density B, the force (F) acting on the charge particle is given by the expression? (KMU MDCAT 2024)
Correct answer: (b) F = qv x B
The magnetic force on a moving charge is the vector product $q\mathbf{v}\times\mathbf{B}$.
8.Electric forces change the magnitude and direction of velocity while magnetic forces change_____________ of velocity (UHS MDCAT 2023)
Correct answer: (b) Only direction
The magnetic force is always at right angles to the velocity, so it can only turn it.
9.The force exerted on charged particle will be maximum when it enters the magnetic field at: (SZABMU MDCAT 2023)
Correct answer: (b) 90O
$F=qvB\sin\theta$ is greatest when the particle crosses the field at a right angle.
10.The magnitude of magnetic force will be maximum on current carrying conductor in uniforrn magnetic field if conductor is placed? (UHS MDCAT 2023)
Correct answer: (c) Perpendicular to magnetic field
$F=BIL\sin\theta$ is greatest when the conductor lies across the field.
11.If electron and proton projected in a magnetic fleld simultaneously then _ _ _ _ will be deflected more: (PMC MDCAT 2022)
Correct answer: (a) Electron
The force is the same but the electron is about two thousand times lighter, so it turns far more sharply.
12.When two positive and negative particles are moving opposite to each other in uniform magnetic field: (PMC MDCAT 2022)
Correct answer: (a) Deflection occurs
Opposite charges moving opposite ways feel forces the same way round, and both are deflected.
13.Force on a proton of charge 2e in a magnetic field of B at 45° while moving with 2 m/s is: (PMC Practice 2021)
Correct answer: (a) 2✓2eB
$F=qvB\sin45^{\circ}=2e\times2\times B\times1/\sqrt2$, that is $2\sqrt2\,eB$.
14.If a charge of 2C is moving with 5m/s enter at 30° in 3 T, calculate the force experienced by it. (PMC Practice 2021)
Correct answer: (b) 15N
$F=qvB\sin30^{\circ}=2\times5\times3\times0.5$, that is $15\,\mathrm{N}$.
15.During the circular path in magnetic field, what is the magnetic force? (PMC Practice 2021)
Correct answer: (d) F = qvB
The magnetic force on a moving charge is $qvB$ when the velocity crosses the field.
16.Which, among the following qualities, is not affected by the magnetic field? (PMC Practice 2021)
Correct answer: (d) Stationary charge
A magnetic force needs motion, so a charge at rest feels nothing.
17.If a conductor of length 7m is placed in a magnetic field of strength 0.3 T carrying current 1 A, parallel to the field. What will be the force, acting on it, due to this magnetic field? (UHS MDCAT 2019)
Correct answer: (b) 0 N
$F=BIL\sin\theta$, and with the current along the field the sine is zero.
18.The horizontal component of Earth magnetic flux density is 1.8 x 10-6 T. The current in a horizontal cable is 160 A. Calculate the maximum force per unit length? (UHS MDCAT 2019)
Correct answer: (b) 2.88x 10-4N/m
$F/L=BI=1.8\times10^{-6}\times160$, that is $2.88\times10^{-4}\,\mathrm{N\,m^{-1}}$.
19.A neutron having mass equal to a proton (mp = 1.6 x 10-27 kg) is moving in a magnetic field of intensity 1.20 x 10-3 T with a speed of 2.0 x 107 ms-1 . What is the maximum force experienced by the neutron? (UHS MDCAT 2018)
Correct answer: (b) 0
A neutron carries no charge, so the magnetic field exerts no force on it.
20.E/m of an electron is given by the relationship. (UHS MDCAT 2018)
Correct answer: (d) e/m=V/Br
With the electric and magnetic forces balanced, $v=E/B$ and $e/m$ works out as $V/Br$.
21.A conductor of length 1m carrying current of 1A is placed parallel to a magnetic field of 1 Gauss. The magnetic force acting on the conductor is: (UHS MDCAT 2017)
Correct answer: (a) Zero
$F=BIL\sin\theta$, and with the current along the field the sine is zero.
22.The force acting on current carrying conductor will be maximum if the angle between magnetic field and conductor is: (UHS MDCAT 2016)
Correct answer: (c) 90°
$F=BIL\sin\theta$ is greatest when the conductor lies across the field.
23.‘F’ is maximum force acting on a conductor. Now if we change the direction of conductor by making an angle of 45° with the magnetic field then the force becomes: (UHS MDCAT 2016)
Correct answer: (c) F/√2
$F=BIL\sin45^{\circ}$, and the sine of $45^{\circ}$ is $1/\sqrt2$.
24.If we doubled all the parameters of the force acting on current carrying conductor and θ = 90° then magnetic force becomes: (UHS MDCAT 2016)
Correct answer: (c) Eight-times
$F=BIL$, and doubling each of the three multiplies the force by eight.