Magnetic Fields and Electromagnetism

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Magnetic Fields and Electromagnetism — Free MYP5 Physics Practice Questions

1QuestionForce acting on current carrying wire in external magnetic fieldConcept Practice

2 marks~3 minCriterion D

An electric motor in a washing machine contains a current-carrying coil placed inside a magnetic field.

Explain how the magnetic force acting on the current-carrying coil produces rotation inside the electric motor. [1]

Explain one societal benefit that washing machines, powered by electric motors, provide to communities. [1]

Solutions

2QuestionMagnetic Materials / Temporary and Permanent MagnetsAssessment Practice

2 marks~3 minCriterion D

A scrapyard crane uses an electromagnet to sort ferromagnetic scrap metal. The electromagnet consists of a coil of wire wound around a soft-iron core.

Explain how switching the current on and off allows the electromagnet to lift and then release scrap metal. [1]

Evaluate why replacing the electromagnet with a permanent magnet would make the crane impractical for this task. [1]

Solutions

3QuestionForce acting on current carrying wire in external magnetic fieldConcept Practice

3 marks~5 minCriterion A

A student investigates the force on a current-carrying wire in a uniform magnetic field of strength

B = 0.2\ \text{T}

. The length of wire inside the field is

L = 0.15\ \text{m}

. The student varies the current

I

and records the force

F

. The graph of

F

against

I

is a straight line passing through the origin.

State the equation relating

F

B

I

, and

L

, and calculate the gradient of the graph. [1]

Explain why the graph is a straight line through the origin. [1]

The student doubles the length of wire inside the field while keeping

B

and

I

constant. Analyse how this change affects the gradient of a new

F

–

I

graph. [1]

Solutions

4QuestionMagnetic Field Around a Bar MagnetAssessment Practice

4 marks~6 minCriterion A

A student places a plotting compass at five positions around a bar magnet, labelled P, Q, R, S, and T, as shown in the diagram. At positions P and S (near the north pole) the needle points away from the magnet; at Q and T (near the south pole) it points toward the magnet; at R (beside the midpoint) it aligns parallel to the magnet's length.

Explain why the compass needle points in a different direction at each position, referring to magnetic field lines and the magnet's poles. [2]

The compass positions are closer together near the poles than near the midpoint. Explain what this spacing suggests about field line density and field strength at those regions. [1]

Evaluate one limitation of using a plotting compass to map the complete magnetic field of a bar magnet. [1]

Solutions

5QuestionField Lines Around Straight Current carrying conductors and SolenoidsAssessment Practice

5 marks~8 minCriterion C

A student investigates the magnetic field inside a solenoid of length

L = 0.50

m with

N = 500

turns. The magnetic flux density

B

(in mT) is measured at the centre for different currents

I

(in A).

I

(A): 0.5, 1.0, 1.5, 2.0, 2.5, 3.0

B

(mT): 1.26, 2.51, 3.77, 5.03, 6.28, 7.54

The magnetic field inside a solenoid is

B = \mu_0 n I

, where

n = N/L

Convert

B

to tesla (T). Construct a graph of

B

(T) against

I

(A), draw a line of best fit, and calculate its gradient. [2]

Deduce an experimental value for

\mu_0

using your gradient and the solenoid dimensions. [2]

The accepted value is

\mu_0 = 4\pi \times 10^{-7}

T·m/A, giving a percentage error of approximately 100%. Analyse one source of systematic error that could cause this result and explain how the experimental setup could be modified to reduce it. [1]

Solutions

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