IB · IB Physics
IB Physics: Motion in electromagnetic fields — Practice Questions & Answers
106 practice questions available for this topic — here are 10 with full answers and explanations.
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Practice questions with answers
1
Multiple choice · Medium
The force on a straight conductor of length $L$ carrying current $I$ at right angles to a field $B$ is:
- $F=BIL$
- $F=\frac{BI}{L}$
- $F=\frac{IL}{B}$
- $F=B+I+L$
Tap an answer to check it.
Why$F=BIL$ when the current is perpendicular to the magnetic field.
2
Multiple choice · Medium
The magnetic force on a charge $q$ moving at speed $v$ perpendicular to a field $B$ is:
- $F=qvB$
- $F=\frac{qv}{B}$
- $F=\frac{qB}{v}$
- $F=qvB^{2}$
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Why$F=qvB$ for motion perpendicular to the field; the force is perpendicular to both $v$ and $B$.
3
Multiple choice · Easy
To find the direction of the force on a current in a magnetic field, one can use:
- Fleming's left-hand rule
- Lenz's law
- The inverse-square law
- Snell's law
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WhyFleming's left-hand rule gives the direction of the force (thrust) for a current in a magnetic field.
4
Multiple choice · Hard
A $0.20\,\text{m}$ wire carries $3.0\,\text{A}$ perpendicular to a $0.50\,\text{T}$ field. What is the force on it?
- $0.30\,\text{N}$
- $3.0\,\text{N}$
- $0.75\,\text{N}$
- $30\,\text{N}$
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Why$F=BIL=0.50\times 3.0\times 0.20=0.30\,\text{N}$.
5
Multiple choice · Medium
A charged particle moving perpendicular to a uniform magnetic field follows a path that is:
- Circular
- A straight line
- Parabolic
- Elliptical and decaying
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WhyThe magnetic force is always perpendicular to the velocity, providing a centripetal force, so the path is circular.
6
Multiple choice · Medium
Two parallel wires carry currents in the same direction. They will:
- Attract each other
- Repel each other
- Exert no force
- Spin in place
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WhyParallel currents in the same direction attract one another; opposite currents repel.
7
Fill in the blank · Easy
The force on a current-carrying conductor, $F=BIL$, is greatest when the field is to the current.
Answer:
perpendicular / at right angles / normal
WhyThe force is maximum when the field is perpendicular to the current and zero when parallel.
8
Fill in the blank · Medium
A charged particle entering a uniform magnetic field at right angles moves in a path.
Answer:
circular / circle
WhyThe constant perpendicular magnetic force acts as a centripetal force, producing circular motion.
9
Multiple choice · Medium
An emf is induced in a conductor when there is a change of magnetic flux linkage. The size of the induced emf depends on which factor?
- The rate of change of magnetic flux linkage
- The total charge on the conductor
- The resistance of the conductor only
- The mass of the conductor
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WhyBy Faraday's law the induced emf is proportional to the rate of change of magnetic flux linkage.
10
Multiple choice · Medium
A straight conductor is moved through a uniform magnetic field. An emf is induced only when the conductor does what?
- Cuts magnetic field lines
- Stays at rest in the field
- Moves parallel to the field lines
- Is removed from the circuit
Tap an answer to check it.
WhyAn emf is induced only when the conductor cuts magnetic field lines (changes the flux linkage).
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