A 12V battery has an internal resistance of 2.0Ω. A load of variable resistance is connected across the battery and adjusted to have resistance equal to that of the internal resistance of the battery. Which statement is correct for this circuit? 

A. The current in the battery is 6A. 
B. The potential difference across the load is 12V. 
C. The power dissipated in the battery is 18W. 
D. The resistance in the circuit is 1.0Ω.

C

The diagram shows the path of a particle in a region of uniform magnetic field. The field is directed into the plane of the page.

This particle could be

A. an alpha particle.

B. a beta particle.

C. a photon.

D. a neutron.

A

Positive charge is uniformly distributed on a semi-circular plastic rod. What is the direction of the electric field strength at point S?

B

Four particles, two of charge +Q and two of charge −Q, are positioned on the $x$-axis as shown. A particle P with a positive charge is placed on the $y$-axis. What is the direction of the net electrostatic force on this particle?

D

A power station generates $250 \mathrm{kW}$ of power at a potential difference of $25 \mathrm{kV}$. The energy is transmitted through cables of total resistance $4.0 \mathrm{\Omega }$.

What is the power loss in the cables?

A.  $0.04 \mathrm{kW}$

B.  $0.4 \mathrm{kW}$

C.  $4 \mathrm{kW}$

D.  $40 \mathrm{kW}$

B

Two wires, X and Y, are made from the same metal. The wires are connected in series. The radius of X is twice that of Y. The carrier drift speed in X is v_X and in Y it is v_Y.

What is the value of the ratio $\frac{{\text{v}}_{\text{X}}}{{\text{v}}_{\text{Y}}}$?

A. 0.25

B. 0.50

C. 2.00

D. 4.00

A

An electron enters the space inside a current-carrying solenoid. The velocity of the electron is parallel to the solenoid’s axis. The electron is

A. slowed down.

B. speeded up.

C. undeflected.

D. deflected outwards.

A

When an electric cell of negligible internal resistance is connected to a resistor of resistance 4R, the power dissipated in the resistor is P.

What is the power dissipated in a resistor of resistance value R when it is connected to the same cell?

A.     $\frac{P}{4}$

B.     P

C.     4P

D.     16P

C

A circuit contains a variable resistor of maximum resistance R and a fixed resistor, also of resistance R, connected in series. The emf of the battery is $6.0 \text{V}$ and its internal resistance is negligible.

What are the initial and final voltmeter readings when the variable resistor is increased from an initial resistance of zero to a final resistance of R?

C

Two parallel wires P and Q are perpendicular to the page and carry equal currents. Point S is the same distance from both wires. The arrow shows the magnetic field at S due to P and Q.

What are the correct directions for the current at P and the current at Q?

A

Two point charges Q₁ and Q₂ are one metre apart. The graph shows the variation of electric potential V with distance $x$ from Q₁.

What is $\frac{Q_1}{Q_2}$?

A.   $\frac{1}{16}$

B.   $\frac{1}{4}$

C.   4

D.   16

D

Two cells are connected in parallel as shown below. Each cell has an emf of 5.0 V and an internal resistance of 2.0 Ω. The lamp has a resistance of 4.0 Ω. The ammeter is ideal.

What is the reading on the ammeter?

A.  1.0 A

B.  1.3 A

C.  2.0 A

D.  2.5 A

A

The correct option (A) was selected with the lowest frequency of the four possible answers. This question has a low difficulty index, suggesting that the majority of candidates found it challenging. Students were asked to apply the concept of resistors in parallel; omitting the internal resistance in parallel to the external lamp resistance was the most common error here. This question is useful for the revision of resistors in combination.

A cell of electromotive force (emf) $E$ and zero internal resistance is in the circuit shown.

What is correct for loop WXYUW?

A.  $E=3I_{1}R-I_{3}R$

B.  $E=I_{3}R-I_{2}R$

C.  $E=I_{3}R$

D.  $E=2I_{2}R-I_{3}R$

D

There are a high number of blanks responses indicating that some candidates decided to leave it until the end. It perhaps looked complicated but pleasingly over half did get the correct answer with choices reasonably evenly balanced between the three wrong answers suggesting that these were guesses.

An ion of charge +Q moves vertically upwards through a small distance s in a uniform vertical electric field. The electric field has a strength E and its direction is shown in the diagram.

What is the electric potential difference between the initial and final position of the ion?

A.     $\frac{EQ}{s}$

B.     EQs

C.     Es

D.     $\frac{E}{s}$

C

A proton of velocity v enters a region of electric and magnetic fields. The proton is not deflected. An electron and an alpha particle enter the same region with velocity v. Which is correct about the paths of the electron and the alpha particle?

D

A cell of emf 6.0 V and negligible internal resistance is connected to three resistors as shown.

The resistors have resistance of 3.0 Ω and 6.0 Ω as shown.

What is the current in resistor X?

A.     0.40 A

B.     0.50 A

C.     1.0 A

D.     2.0 A

C

In an experiment to determine the resistivity of a material, a student measures the resistance of several wires made from the pure material. The wires have the same length but different diameters.

Which quantities should the student plot on the $x$-axis and the $y$-axis of a graph to obtain a straight line?

C

Two currents of 3 A and 1 A are established in the same direction through two parallel straight wires R and S.

What is correct about the magnetic forces acting on each wire?

A. Both wires exert equal magnitude attractive forces on each other.

B. Both wires exert equal magnitude repulsive forces on each other.

C. Wire R exerts a larger magnitude attractive force on wire S.

D. Wire R exerts a larger magnitude repulsive force on wire S.

A

This question had the lowest difficulty index on the HL paper, with roughly 10 % of candidates selecting response A. Responses C and D were roughly equally common candidate answers, with students not recognizing the applicability of Newton’s 3rd law.

Electrons, each with a charge e, move with speed v along a metal wire. The electric current in the wire is I.

Plane P is perpendicular to the wire. How many electrons pass through plane P in each second?

A.  $\frac{e}{I}$

B.  $\frac{ve}{I}$

C.  $\frac{I}{ve}$

D.  $\frac{I}{e}$

D

Two parallel plates are a distance apart with a potential difference between them. A point charge moves from the negatively charged plate to the positively charged plate. The charge gains kinetic energy W. The distance between the plates is doubled and the potential difference between them is halved. What is the kinetic energy gained by an identical charge moving between these plates?

A. $\frac{W}{2}$

B. W

C. 2W

D. 4W

A

The correct response (A) was the most common from candidates, however a significant number of candidates appeared unsure of the impact of the distance between plates and (incorrectly) selected response B.

A conductor is placed in a uniform magnetic field perpendicular to the plane of the paper. A force F acts on the conductor when there is a current in the conductor as shown.

The conductor is rotated 30° about the axis of the magnetic field.

What is the direction of the magnetic field and what is the magnitude of the force on the conductor after the rotation?

C

This question requires careful reading by the candidate. Candidates needed to appreciate that the rotation relative to the magnetic field axis still produces a 90 degree angle between the conductor and the field. Option D was a very effective distractor for students.

An electrical power supply has an internal resistance. It supplies a direct current $I$ to an external circuit for a time $t$. What is the electromotive force (emf) of the power supply?

A.  $\frac{\mathrm{total} \mathrm{energy} \mathrm{transferred} \mathrm{to} \mathrm{the} \mathrm{whole} \mathrm{circuit}}{I\times t}$

B.  $\frac{\mathrm{total} \mathrm{power} \mathrm{transferred} \mathrm{to} \mathrm{the} \mathrm{whole} \mathrm{circuit}}{I\times t}$

C.  $\frac{\mathrm{total} \mathrm{energy} \mathrm{transferred} \mathrm{to} \mathrm{the} \mathrm{external} \mathrm{circuit}}{I\times t}$

D.  $\frac{\mathrm{total} \mathrm{power} \mathrm{transferred} \mathrm{to} \mathrm{the} \mathrm{external} \mathrm{circuit}}{I\times t}$

A

The coil of a direct current electric motor is turning with a period T. At t = 0 the coil is in the position shown in the diagram. Assume the magnetic field is uniform across the coil.

Which graph shows the variation with time of the force exerted on section XY of the coil during one complete turn?

A

Has a negative discrimination index with over 80% of candidates choosing the incorrect answer. The difficulty index is also low. The question states that it is about a direct current electric motor, suggesting that C and D are incorrect so by choosing them it would seem that some candidates are confusing an electric motor with a generator.

What is the relationship between the resistivity $\rho$ of a uniform wire, the radius $r$ of the wire and the length $l$ of the wire when its resistance is constant?

A.  $\rho \propto r^{2}l$

B.  $\rho \propto r{l}^2$

C.  $\rho \propto \frac{l}{r^2}$

D.  $\rho \propto \frac{r^2}{l}$

D

It was pointed out on the G2s that the proportional symbol is incorrect. The high number of correct responses indicates that it did not disadvantage the students and will be corrected for publication.

Two parallel wires carry equal currents in the same direction out of the paper. Which diagram shows the magnetic field surrounding the wires?

A

A horizontal electrical cable carries a steady current out of the page. The Earth’s magnetic field exerts a force on the cable.

Which arrow shows the direction of the force on the cable due to the Earth’s magnetic field?

B

The correct answer was well answered by candidates, with a relatively high discrimination index.

The force acting between two point charges is $F$ when the separation of the charges is $x$. What is the force between the charges when the separation is increased to $3x$?

A. $\frac{F}{3}$

B. $\frac{F}{3x^2}$

C. $\frac{F}{9}$

D. $\frac{F}{9x^2}$

C

A resistor of resistance R is connected to a fully charged cell of negligible internal resistance. A constant power P is dissipated in the resistor and the cell discharges in time t. An identical cell is connected in series with two identical resistors each of resistance R.

What is the power dissipated in each resistor and the time taken to discharge the cell?

B

This question was not well answered, with fewer than 25 % of candidates correctly selecting response B. Furthermore, the discrimination index for this question was remarkably low, suggesting this question would provide rich classroom discussion.

In the circuit shown, the battery has an emf of 12 V and negligible internal resistance. Three identical resistors are connected as shown. The resistors each have a resistance of 10 Ω.

The resistor L is removed. What is the change in potential at X?

A.  Increases by 2 V

B.  Decreases by 2 V

C.  Increases by 4 V

D.  Decreases by 4 V

B

The majority of HL candidates correctly determined the magnitude of the potential but determining the direction of the change was more problematic. More candidates (incorrectly) selected option A than the correct option B, reinforcing the importance of a conceptual understanding of circuits and potential change.

A cell has an emf of 3.0 V and an internal resistance of 2.0 Ω. The cell is connected in series with a resistance of 10 Ω.

What is the terminal potential difference of the cell?

A.  0.5 V

B.  1.5 V

C.  2.5 V

D.  3.0 V

C

The diagram shows the magnetic field surrounding two current-carrying metal wires P and Q. The wires are parallel to each other and at right angles to the plane of the page.

What is the direction of the electron flow in P and the direction of the electron flow in Q?

B

A capacitor of capacitance 1.0 μF stores a charge of 15 μC. The capacitor is discharged through a 25 Ω resistor. What is the maximum current in the resistor?

A.  0.60 mA

B.  1.7 mA

C.  0.60 A

D.  1.7 A

C

Two power supplies, one of constant emf 24 V and the other of variable emf P, are connected to two resistors as shown. Both power supplies have negligible internal resistances.

What is the magnitude of P for the reading on the ammeter to be zero?

A. Zero

B. 6 V

C. 8 V

D. 18 V

B