IB Physics SL D 2 Electric and Magnetic Fields Questions

Practise IB Physics SL D.2 by analysing charge interactions, charge transfer, electric-field patterns and uniform plate fields, alongside magnetic field-line direction.

Exam points

Use Coulomb’s law to calculate forces between point charges and determine whether the charges attract or repel.
Apply conservation of charge to determine an unknown charge in a particle reaction.
Use grounding and induction to infer electron redistribution and the conductor’s net charge.
Calculate E=F/q or the point-charge field, then combine field vectors from multiple charges.
Use F=qE and Newton’s second law to calculate a charged particle’s acceleration or describe its motion.
Read electric-field lines for direction and charge arrangement, and compare field strength from their density.
Calculate the uniform field between parallel plates with E=V/d using their potential difference and separation.
Draw magnetic-field lines around a current-carrying wire and infer their direction from current.

Covered syllabus points

D.2.1—Electric charge forces D.2.2—Coulomb’s law D.2.3—Charge conservation D.2.4—Millikan experiment D.2.5—Charge transfer D.2.6—Electric field strength D.2.7—Electric field lines D.2.8—Field-line density D.2.9—Parallel-plate field D.2.10—Magnetic field lines

[Maximum number: 2]

Ion-thrust engines can power spacecraft. In this type of engine, ions are created in a chamber and expelled from the spacecraft. The spacecraft is in outer space when the propulsion system is turned on. The spacecraft starts from rest.

The mass of ions ejected each second is $6.6 \times 10^{-6} \mathrm{~kg}$ and the speed of each ion is $5.2 \times 10^{4} \mathrm{~m} \mathrm{~s}^{-1}$ . The initial total mass of the spacecraft and its fuel is 740 kg . Assume that the ions travel away from the spacecraft parallel to its direction of motion.

In practice, the ions leave the spacecraft at a range of angles as shown.

Outline why the ions are likely to spread out.

[Maximum number: 8]

This question is in two parts. Part 1 is about simple harmonic motion and forced oscillations. Part 2 is about electric and magnetic force fields.

Part 1 Simple harmonic motion and forced oscillations
The graph shows the variation with time of the displacement of an object undergoing simple harmonic motion.
displacement / mm

time / ms

(a)

Part 2 Electric and magnetic force fields

[ 8 ]

(i)

Define electric field strength.

[ 2 ]

(ii)

The diagram shows a pair of horizontal metal plates. Electrons can be deflected vertically using an electric field between the plates.

Figure for Question (ii) — IB Physics SL

[ 4 ]

(i)

Draw the shape and direction of the electric field between the plates on the diagram.

[ 2 ]

(ii)

Calculate the force on an electron between the plates when the electric field strength has a value of $2.5 \times 10^{3} \mathrm{NC}^{-1}$ .

[ 2 ]

$F=2.5 \times 10^{3} \times 1.6 \times 10^{-19}$ ;
$4.0 \times 10^{-16} \mathrm{~N}$ ;

Marking guidance:

Award [2] for a bald correct answer.

(iii)

The diagram shows two isolated electrons, X and Y , initially at rest in a vacuum. The initial separation of the electrons is 5.0 mm . The electrons subsequently move apart in the directions shown.

Figure for Question (iii) — IB Physics SL

[ 2 ]

(i)

Show that the initial electric force acting on each electron due to the other electron is approximately $9 \times 10^{-24} \mathrm{~N}$ .

[ 2 ]

(c) (i) use of $F=\frac{\left(1.60 \times 10^{-19}\right)^{2}}{4 \pi \varepsilon_{0}\left(5.0 \times 10^{-3}\right)^{2}}$ or $F=\frac{\left(1.60 \times 10^{-19}\right)^{2}}{\left(5.0 \times 10^{-3}\right)^{2}} \times 8.99 \times 10^{9}$ ;
$9.2 \times 10^{-24} \mathrm{~N} ;$

[Maximum number: 1]

The diagram shows a junction in a circuit.

The currents in the three wires are related by $I_{1}=I_{2}+I_{3}$ .
State the fundamental law of Physics from which this relation is derived.

[Maximum number: 2]

time / ms

Part 2 Electric and magnetic force fields

The diagram shows two isolated electrons, X and Y , initially at rest in a vacuum. The initial separation of the electrons is 5.0 mm . The electrons subsequently move apart in the directions shown.

Show that the initial electric force acting on each electron due to the other electron is approximately $9 \times 10^{-24} \mathrm{~N}$ .

[Maximum number: 1]

A positively charged rod is near a metal plate that is grounded as shown.

The grounding wire and then the rod are removed. What is correct about the overall charge on the plate before and after grounding is removed?

Charge on plate before

grounding is removed

Charge on plate after

grounding is removed

neutral

negative

neutral

negative

[Maximum number: 2]

time / ms

Part 2 Electric and magnetic force fields

The diagram shows a pair of horizontal metal plates. Electrons can be deflected vertically using an electric field between the plates.

Draw the shape and direction of the electric field between the plates on the diagram.

[Maximum number: 1]

The diagram shows electrostatic field lines. The source of the field is not shown.

At which position in the field would a negative point charge experience the greatest force to the right?

[Maximum number: 1]

Two oppositely charged parallel plates are a distance 8.0 cm apart. The potential difference between the plates is 120 V . An alpha particle is placed on the positively charged plate and released from rest. Gravity is ignored.

Calculate the electric field between the plates.

$E=\ll \frac{120}{8.0 \times 10^{-2}}=>1.5 \times 10^{3} N C^{-1} \boldsymbol{O} \boldsymbol{R} \mathrm{Vm}^{-1}$

[1]

[Maximum number: 2]

On the diagram below, sketch the magnetic field pattern around the long straight current-carrying conductor. The direction of the current is into the plane of the paper.

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Covered syllabus points

Question 1

Question 2

Question (a)

Question (i)

Question (ii)

Question (i)

Question (ii)

Question (iii)

Question (i)

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9