IB Physics HL D 2 Electric and Magnetic Fields Questions

Practise IB Physics HL D.2 by analysing charge interactions, electric and magnetic fields, potential energy and electric potential, work, and equipotential patterns.

Exam points

Determine attraction or repulsion and calculate point-charge forces with Coulomb’s law, including superposed forces.
Apply conservation of charge to particle reactions and charge redistribution between objects.
Interpret Millikan’s oil-drop experiment as evidence that electric charge is quantized.
Trace electron transfer to explain charging by contact or friction and the resulting sign of charge.
Calculate electric field strength from force per unit charge and combine field vectors from several sources.
Draw or interpret electric field-line direction and use line density to compare field strength.
Calculate the uniform field between parallel plates from potential difference and separation, then relate it to charge force.
Draw or interpret magnetic-field patterns and directions around magnets and current-carrying wires.
Relate electric potential energy to the work required to assemble a system of charges from infinite separation.
Calculate two-point-charge potential energy with its sign and distinguish it from electric potential.
Treat electric potential as a scalar, combine contributions from charges, and apply the zero-at-infinity reference.
Calculate electric potential around a point charge and use its spatial gradient to determine field strength and direction.
Use work qΔV and equipotential diagrams to analyse energy changes, zero work along an equipotential, and the perpendicular field direction.

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 D.2.11 (HL)—Electric potential energy D.2.12 (HL)—Two-charge potential energy D.2.13 (HL)—Electric potential as scalar D.2.14 (HL)—Electric potential D.2.15 (HL)—Electric potential gradient D.2.16 (HL)—Work in electric fields D.2.17 (HL)—Electric equipotentials D.2.18 (HL)—Equipotentials and electric fields

[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: 10]

This question is in two parts. Part 1 is about photoelectricity. Part 2 is about electrical and magnetic force fields.
Part 1 Photoelectricity

(a)

Define electric field strength.

[ 2 ]

(b)

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

[ 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.

(c)

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.

[ 4 ]

(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 $F=\frac{\left(1.60 \times 10^{-19}\right)^{2}}{\left(5.0 \times 10^{-3}\right)^{2}} \times 8.99 \times 10^{9}$ ;
$9.2 \times 10^{-24} \mathrm{~N} ;$

(ii)

The diagram shows Y as seen from X , at one instant. Y is moving into the plane of the paper. For this instant, draw on the diagram the shape and direction of the magnetic field produced by Y .

[ 2 ]

[Maximum number: 1]

Deuterium, ${ }_{1}^{2} \mathrm{H}$ , undergoes fusion according to the following reaction.

{ }_{1}^{2} \mathrm{H}+{ }_{1}^{2} \mathrm{H} \rightarrow{ }_{1}^{3} \mathrm{H}+\mathrm{X}

Particle Y is produced in the collision of a proton with a $\mathrm{K}^{-}$ in the following reaction.

\mathrm{K}^{-}+\mathrm{p}^{+} \rightarrow \mathrm{K}^{0}+\mathrm{K}^{+}+\mathrm{Y}

The quark content of some of the particles involved are

\mathrm{K}^{-}=\overline{\mathrm{u}} \mathrm{~s} \quad \mathrm{~K}^{0}=\mathrm{d} \overline{\mathrm{~s}}

Identify, for particle Y , the

charge.

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Covered syllabus points

Question 1

Question 2

Question (a)

Question (b)

Question (i)

Question (ii)

Question (c)

Question (i)

Question (ii)

Question 3