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Moving Charges and Magnetism Physics - Moving Charges and Magnetism

Gujarat Board (GSEB) - STD 12 Science - Physics (GSEB - English Medium). 582 questions in this chapter.

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Moving Charges and Magnetism question types

582 questions across 7 question groups — pick any mix to generate a Physics paper with step-by-step answer keys.

582
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7
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5
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Sample Questions

Moving Charges and Magnetism questions

One sample from each question group in this chapter. Select any group above to see the full set with answer keys.

Q 1M.C.Q (1 Marks)1 Mark
Consider a wire carrying a steady current, I placed in a uniform magnetic field B perpendicular to its length. Consider the charges inside the wire. It is known that magnetic forces do no work. This implies that:
  • A
    Motion of charges inside the conductor is unaffected by B since they do not absorb energy.
  • B
    Some charges inside the wire move to the surface as a result of B.
  • C
    If the wire moves under the influence of B, no work is done by the magnetic force on the ions, assumed fixed within the wire.
  • ✓
    B and C both

Answer: D.

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Q 2M.C.Q (1 Marks)1 Mark
A charged particle moves through a magnetic field perpendicular to its direction. Then:
  • A
    Kinetic energy changes, but the momentum is constant.
  • ✓
    The momentum changes, but the kinetic energy is constant.
  • C
    Both momentum and kinetic energy of the particle are not constant.
  • D
    Both momentum and kinetic energy of the particle are constant.

Answer: B.

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Q 3M.C.Q (1 Marks)1 Mark
A particle of mass $m$ and charge $q$ enters a magnetic field $B$ perpendicularly with $a$ velocity $v$. The radius of the circular path described by it will be:
  • A
    $Bq/mv.$
  • B
    $mq/Bv.$
  • C
    $mB/qv.$
  • ✓
    $mv/Bq.$

Answer: D.

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Q 4M.C.Q (1 Marks)1 Mark
An electron having a charge e moves with a velocity v in $X-$direction. An electric field acts on it in $Y-$direction? The force on the electron acts in:
  • A
    Positive direction of $Y-$axis.
  • ✓
    Negative direction of $Y-$axis.
  • C
    Positive direction of $Z-$axis.
  • D
    Negative direction of $Z-$axis.

Answer: B.

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Q 5M.C.Q (1 Marks)1 Mark
When a charged particle moves through a magnetic field, the quantity which is not affected in the magnetic field is:
  • A
    Particle velocity
  • B
    Particle acceleration
  • C
    Linear momentum of the particle
  • ✓
    Kinetic energy of the particle

Answer: D.

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Q 6Assertion (A) & Reason (B) MCQ1 Mark
Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is NOT the correct explanation of A.
  3. A is true but R is false.
  4. A is false and R is also false.
Assertion (A): When a charged particle moves perpendicular to magnetic field then its kinetic energy and momentum gets affected.
Reason (R): Force changes velocity of charged particle.
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Q 7Assertion (A) & Reason (B) MCQ1 Mark
Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is NOT the correct explanation of A.
  3. A is true but R is false.
  4. A is false and R is also false.
Assertion (A): A solenoid tends to expand, when a current passes through it.
Reason (R): Two straight parallel metallic wires carrying current in same direction repel each other.
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Q 8Assertion (A) & Reason (B) MCQ1 Mark
Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is NOT the correct explanation of A.
  3. A is true but R is false.
  4. A is false and R is also false.
Assertion (A): A charge, whether stationary or in motion produces a magnetic field around it.
Reason (R): Moving charges produce only electric field in the surrounding space.
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Q 9Assertion (A) & Reason (B) MCQ1 Mark
Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is NOT the correct explanation of A.
  3. A is true but R is false.
  4. A is false and R is also false.
Assertion (A): The magnetic field intensity at the centre of a circular coil carrying current changes, if the current through the coil is doubled.
Reason (R): The magnetic field intensity is dependent on current in conductor.
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Q 10Assertion (A) & Reason (B) MCQ1 Mark
Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is NOT the correct explanation of A.
  3. A is true but R is false.
  4. A is false and R is also false.
Assertion (A): Magnetic field lines can be entirely confined within the core of a toroid, but not within a straight solenoid.
Reason (R): The magnetic field inside the solenoid is uniform.
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Q 111 Marks Question1 Mark
Answer the following question:
An electron travelling west to east enters a chamber having a uniform electrostatic field in north to south direction. Specify the direction in which a uniform magnetic field should be set up to prevent the electron from deflecting from its straight line path.
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Q 121 Marks Question1 Mark
Answer the following question:
A charged particle enters an environment of a strong and non-uniform magnetic field varying from point to point both in magnitude and direction, and comes out of it following a complicated trajectory. Would its final speed equal the initial speed if it suffered no collisions with the environment?
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Q 131 Marks Question1 Mark
A straight horizontal conducting rod of length 0.45 m and mass 60 g is suspended by two vertical wires at its ends. A current of 5.0 A is set up in the rod through the wires.
  1. What magnetic field should be set up normal to the conductor in order that the tension in the wires is zero?
  2. What will be the total tension in the wires if the direction of current is reversed keeping the magnetic field same as before? (Ignore the mass of the wires.) $g = 9.8 m s^{-2}$.
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Q 141 Marks Question1 Mark
Answer the following question:
A magnetic field that varies in magnitude from point to point but has a constant direction (east to west) is set up in a chamber. A charged particle enters the chamber and travels undeflected along a straight path with constant speed. What can you say about the initial velocity of the particle?
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Q 151 Marks Question1 Mark
A planar loop of rectangular shape is moved within the region of a uniform magnetic field acting perpendicular to its plane. What is the direction and magnitude of the current induced in it?
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Q 162 Marks Questions2 Marks
A magnetic field of $100 \mathrm{G}\left(1 \mathrm{G}=10^{-4} \mathrm{~T}\right)$ is required which is uniform in a region of linear dimension about 10 cm and area of cross-section about $10^{-3} \mathrm{~m}^2$. The maximum current-carrying capacity of a given coil of wire is 15 A and the number of turns per unit length that can be wound round a core is at most 1000 turns $\mathrm{m}^{-1}$. Suggest some appropriate design particulars of a solenoid for the required purpose. Assume the core is not ferromagnetic.
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Q 172 Marks Questions2 Marks
A circular coil of N turns and radius R carries a current I. It is unwound and rewound to make another coil of radius R/2, current I remaining the same. Calculate the ratio of the magnetic moments of the new coil and the original coil.
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Q 182 Marks Questions2 Marks
A steady current $\left(I_1\right)$ flows through a long straight wire. Another wire carrying steady current $\left(I_2\right)$ in the same direction is kept close and parallel to the first wire. Show with the help of a diagram how the magnetic field due to the current $\mathrm{I}_1$ exerts a magnetic force on the second wire. Write the expression for this force.
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Q 192 Marks Questions2 Marks
Write the expression for Lorentz magnetic force on a particle of charge 'q' moving with velocity$\overrightarrow{\text{v}}$ in a magnetic field $\overrightarrow{\text{B}}.$ Show that no work is done by this force on the charged particle.
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Q 213 Marks Question3 Marks
  1. Obtain the expression for the cyclotron frequency.
  2. A deuteron and a proton are accelerated by the cyclotron. Can both be accelerated with the same oscillator frequency? Give reason to justify your answer.
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Q 223 Marks Question3 Marks
A square coil of side 10 cm consists of 20 turns and carries a current of 12 A. The coil is suspended vertically and the normal to the plane of the coil makes an angle of 30º with the direction of a uniform horizontal magnetic field of magnitude 0.80 T. What is the magnitude of torque experienced by the coil?
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Q 233 Marks Question3 Marks
The wires which connect the battery of an automobile to its starting motor carry a current of 300 A (for a short time). What is the force per unit length between the wires if they are 70 cm long and 1.5 cm apart? Is the force attractive or repulsive?
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Q 243 Marks Question3 Marks
A circular coil of wire consisting of 100 turns, each of radius 8.0 cm carries a current of 0.40 A. What is the magnitude of the magnetic field B at the centre of the coil?
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Q 253 Marks Question3 Marks
In Exercise 4.11 obtain the frequency of revolution of the electron in its circular orbit. Does the answer depend on the speed of the electron? Explain.
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Q 265 Marks Questions5 Marks
  1. Deduce an expression for the frequency of revolution of a charged particle in a magnetic field and show that it is independent of velocity or energy of the particle.
  2. Draw a schematic sketch of a cyclotron. Explain, giving the essential details of its construction, how it is used to accelerate the charged particles.
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Q 275 Marks Questions5 Marks
  1. Draw a labelled diagram of a moving coil galvanometer. Describe briefly its principle and working.
  2. Answer the following:
  1. Why is it necessary to introduce a cylindrical soft iron core inside the coil of a galvanometer?
  2. Increasing the current sensitivity of a galvanometer may not necessarily increase its voltage sensitivity. Explain, giving reason.
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Q 285 Marks Questions5 Marks
  1. Draw a schematic sketch of a cyclotron. Explain clearly the role of crossed electric and magnetic field in accelerating the charge. Hence derive the expression for the kinetic energy acquired by the particles.
  2. An α–particle and a proton are released from the centre of the cyclotron and made to accelerate.
    1. Can both be accelerated at the same cyclotron frequency? Give reason to justify your answer.
    2. When they are accelerated in turn, which of the two will have higher velocity at the exit slit of the dees?
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Q 295 Marks Questions5 Marks
  1. Using Biot-Savart’s law, derive the expression for the magnetic field in the vector form at a point on the axis of a circular current loop.
  2. What does a toroid consist of ? Find out the expression for the magnetic field inside a toroid for N turns of the coil having the average radius r and carrying a current I. Show that the magnetic field in the open space inside and exterior to the toroid is zero.
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Q 305 Marks Questions5 Marks
  1. Explain briefly the principle on which a transistor-amplifier works as an oscillator. Draw the necessary circuit diagram and explain its working.
  2. Identify the equivalent gate for the following circuit and write its truth table.
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Q 31Case study (4 Marks)4 Marks
A magnetic field set up using Helmholtz coils (described in Exercise 4.16) is uniform in a small region and has a magnitude of 0.75 T. In the same region, a uniform electrostatic field is maintained in a direction normal to the common axis of the coils. A narrow beam of (single species) charged particles all accelerated through 15 kV enters this region in a direction perpendicular to both the axis of the coils and the electrostatic field. If the beam remains undeflected when the electrostatic field is $9.0 \times 10^{–5} V m^{–1},$ make a simple guess as to what the beam contains. Why is the answer not unique?
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Q 32Case study (4 Marks)4 Marks
A uniform magnetic field of 1.5 T exists in a cylindrical region of radius10.0 cm, its direction parallel to the axis along east to west. A wire carrying current of 7.0 A in the north to south direction passes through this region. What is the magnitude and direction of the force on the wire if,
  1. The wire intersects the axis,
  2. The wire is turned from N-S to northeast-northwest direction,
  3. The wire in the N-S direction is lowered from the axis by a distance of 6.0 cm?
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Q 33Case study (4 Marks)4 Marks
A uniform magnetic field of 3000 G is established along the positive z-direction. A rectangular loop of sides 10 cm and 5 cm carries a current of 12 A. What is the torque on the loop in the different cases shown in Fig.? What is the force on each case? Which case corresponds to stable equilibrium?
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Q 34Case study (4 Marks)4 Marks
For a circular coil of radius R and N turns carrying current I, the magnitude of the magnetic field at a point on its axis at a distance x from its centre is given by,
$\text{B}=\frac{\mu_{0}\text{IR}^{2}\text{N}}{2(\text{x}^{2}+\text{R}^{2})^{\frac{3}{2}}}$
  1. Show that this reduces to the familiar result for field at the centre of the coil.
  2. Consider two parallel co-axial circular coils of equal radius R, and number of turns N, carrying equal currents in the same direction, and separated by a distance R. Show that the field on the axis around the mid-point between the coils is uniform over a distance that is small as compared to R, and is given by,$\text{B}=0.72\frac{\mu_{0}\text{NI}}{\text{R}}$, approximately.
[Such an arrangement to produce a nearly uniform magnetic field over a small region is known as Helmholtz coils.]
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Q 35Case study (4 Marks)4 Marks
A solenoid 60 cm long and of radius 4.0 cm has 3 layers of windings of 300 turns each. A 2.0 cm long wire of mass 2.5 g lies inside the solenoid (near its centre) normal to its axis; both the wire and the axis of the solenoid are in the horizontal plane. The wire is connected through two leads parallel to the axis of the solenoid to an external battery which supplies a current of 6.0 A in the wire. What value of current (with appropriate sense of circulation) in the windings of the solenoid can support the weight of the wire? $g = 9.8\ m\ s^{–2}.$
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