IB · IB Physics
IB Physics: Electric and magnetic fields — Practice Questions & Answers
168 practice questions available for this topic — here are 10 with full answers and explanations.
Start an interactive quiz on Electric and magnetic fields →
Practice questions with answers
1
Multiple choice · Medium
Coulomb's law for the force between two point charges is:
- $F=\frac{kq_{1}q_{2}}{r^{2}}$
- $F=\frac{kq_{1}q_{2}}{r}$
- $F=kq_{1}q_{2}r^{2}$
- $F=\frac{k(q_{1}+q_{2})}{r^{2}}$
Tap an answer to check it.
Why$F=\frac{kq_{1}q_{2}}{r^{2}}$, an inverse-square law analogous to gravitation but for charge.
2
Multiple choice · Easy
Electric field strength is defined as:
- Force per unit charge
- Charge per unit force
- Force per unit mass
- Charge per unit area
Tap an answer to check it.
Why$E=\frac{F}{q}$, the electric force per unit positive charge, measured in $\text{N C}^{-1}$.
3
Multiple choice · Easy
Two charges of the same sign placed near each other will:
- Repel each other
- Attract each other
- Exert no force
- Combine into a neutral particle
Tap an answer to check it.
WhyLike charges repel; opposite charges attract.
4
Multiple choice · Medium
The magnetic field around a long straight current-carrying wire forms:
- Concentric circles around the wire
- Straight lines parallel to the wire
- Radial lines pointing outward
- No field at all
Tap an answer to check it.
WhyThe field forms concentric circles around the wire, with direction given by the right-hand grip rule.
5
Multiple choice · Medium
Electric field lines between two parallel charged plates are:
- Uniform, parallel and evenly spaced
- Radial from the centre
- Circular loops
- Randomly oriented
Tap an answer to check it.
WhyBetween parallel plates (away from edges) the field is uniform, shown by evenly spaced parallel lines from positive to negative plate.
6
Multiple choice · Hard
A charge of $2.0\times 10^{-6}\,\text{C}$ experiences a force of $0.10\,\text{N}$ in an electric field. What is the field strength?
- $5.0\times 10^{4}\,\text{N C}^{-1}$
- $2.0\times 10^{-7}\,\text{N C}^{-1}$
- $0.20\,\text{N C}^{-1}$
- $5.0\times 10^{-4}\,\text{N C}^{-1}$
Tap an answer to check it.
Why$E=\frac{F}{q}=\frac{0.10}{2.0\times 10^{-6}}=5.0\times 10^{4}\,\text{N C}^{-1}$.
7
Fill in the blank · Easy
Two electric charges with the same sign will each other.
Answer:
repel
WhyLike charges repel, while unlike charges attract.
8
Fill in the blank · Medium
The SI unit of magnetic flux density is the .
Answer:
tesla / T
WhyMagnetic flux density $B$ is measured in tesla (T), where $1\,\text{T}=1\,\text{kg s}^{-2}\text{A}^{-1}$.
9
Multiple choice · Hard
Two identical point charges Q1 and Q2 separated by distance d each feel force F. If Q1 is halved, what are the forces on Q1 and Q2?
- F/2 on each charge
- F on each charge
- F/2 on Q1 and F on Q2
- F on Q1 and F/2 on Q2
Tap an answer to check it.
WhyCoulomb force is proportional to the product of the charges, so it halves to F/2; by Newton third law both charges feel the same force F/2.
10
Multiple choice · Medium
The electrostatic forces that two point charges exert on each other are
- equal and opposite
- unequal if the charges differ
- in the same direction
- zero if the charges differ
Tap an answer to check it.
Whyequal in magnitude and opposite in direction (Newton third law).
Practise other IB Physics topics