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D.2 Electric and magnetic fields Topic Practice

D.2 Electric and magnetic fields Topic Practice
IB Physics syllabusPhysics SL/HLFirst assessment 2025

Reason with electric and magnetic field situations by linking diagrams, inverse-square relations and charge conservation.

Exam points

  • read an electric field diagram using line direction and line density to infer field direction and relative strength
  • apply E or F inverse-square equations to locate a zero-field point or compare resultant fields from charges
  • use charge conservation at a circuit junction to write current relations, not just name Kirchhoff’s law

Question 3(a)

[Maximum number: 2]

Two identical conducting spheres X and Y that carry positive charges are separated by a centre-to-centre distance of 24.0 cm in a vacuum. The charge on X is 9 Q and the charge on Y is Q. Point R is 6.0 cm from the centre of Y, as shown.

Question image

The resultant electric field at R is 32.6MNC−132.6 \mathrm{MNC}^{-1}. Determine Q, giving an appropriate unit.

Question 3(a)

[Maximum number: 2]

Two identical conducting spheres X and Y that carry positive charges are separated by a centre-to-centre distance of 24.0 cm in a vacuum. The charge on X is 9 Q and the charge on Y is Q. Point R is 6.0 cm from the centre of Y, as shown.

Question image

The resultant electric field at R is 32.6MNC−132.6 \mathrm{MNC}^{-1}. Determine Q, giving an appropriate unit.

Question 19

[Maximum number: 1]

Two point charges, -Q and +Q, are placed as shown. Point P is at the same distance from both charges.

What is the direction of the electric field strength at P ?

Question image
∘∘−Q+Q\begin{array}{cc} \circ & \circ \\ -Q & +Q \end{array}

Question 19

[Maximum number: 1]

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

Question image

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

neutral

neutral

negative

negative

neutral

negative

negative

Question 26

[Maximum number: 1]

Two point charges, +Q and -Q, are at a distance d from each other.

What is the magnitude of the electric field strength midway between the charges?

A

Zero

B

2kQd2\frac{2 k Q}{d^{2}}

C

4kQd2\frac{4 k Q}{d^{2}}

D

8kQd2\frac{8 k Q}{d^{2}}

Question 27

[Maximum number: 1]

Two points R and S are in a uniform electric field of strength E, directed vertically downwards. The horizontal distance from R to S is Δx\Delta x, and the vertical distance from R to S is Δy\Delta y.

Question image

The electric potential at R is zero. What is the electric potential at S ?

A

EΔx2+Δy2E \sqrt{\Delta x^{2}+\Delta y^{2}}

B

EΔyE \Delta y

C

−EΔx2+Δy2-E \sqrt{\Delta x^{2}+\Delta y^{2}}

D

−EΔy-E \Delta y

Question 31

[Maximum number: 1]

An electron with speed v enters the region between two charged parallel plates midway between the plates, as shown. The potential difference between the plates is V.

Question image

What is the speed of the electron on impact with the plate?

A

v2+eV2me\sqrt{v^{2}+\frac{e V}{2 m_{e}}}

B

v2+(eV2me)2\sqrt{v^{2}+\left(\frac{e V}{2 m_{e}}\right)^{2}}

C

v2+eVme\sqrt{v^{2}+\frac{e V}{m_{e}}}

D

v2+(eVme)2\sqrt{v^{2}+\left(\frac{e V}{m_{e}}\right)^{2}}

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