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7.3.1Magnetism and Electromagnetism

Electromagnetic (EM) Induction

5 min read 8 parts Lesson 11 of 17 Unit quiz

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Section 1 of 8Electromagnetic (EM) Induction

The speed
  • The speed The speed at which the wire, coil or magnet is moved: Increasing the speed will increase the rate at which the magnetic field lines are cut This will increase the induced potential difference 2
The size of the coils
  • The size of the coils Increasing the area of the coils will increase the potential difference induced This is because there will be more wire to cut through the magnetic field lines 4
The strength
  • The strength The strength of the magnetic field: Increasing the strength of the magnetic field will increase the potential difference induced 5
The orientation
  • The orientation The orientation of the poles of the magnet: Reversing the direction in which the wire, coil or magnet is moved Worked Example A coil of wire is connected to a sensitive voltmeter
When a magnet
  • When a magnet is pushed into the coil the needle on the voltmeter will deflect to the right as shown in the diagram below

Section 2 of 8Applications of the Generator Effect

1
Applications of the Generator Effect The generator effect can be used to: Generate a.c in an alternator Generate d.c in a dynamo Alternators An alternator, or a.c
2
in the coil can be measured by adding a galvanometer (centre- zero meter) to the external circuit A p.d
3
is induced in the coil as it cuts the magnetic field The pointer defects first one way, then the opposite way, and then back again This indicates the size and direction of the p.d
4
is constantly changing As a result of the alternating p.d., an alternating current is also produced as the coil rotates This continues as long as the coil keeps turning in the same direction Motion of an alternator The size and direction of the induced p.d
5
(and current) depend on the orientation of the coil with the field A maximum p.d

Section 3 of 8Graphs of Potential Difference in the Coil

Graphs of Potential Difference in the Coil
Is at
  • Is at is at a maximum), the graph is a cosine curve When it starts from a vertical position (p.d
Is zero),
  • Is zero), is zero), the graph is a sine curve Graph of induced p.d
With angle
  • With angle with angle for an alternator Alternating p.d
With corresponding
  • With corresponding with corresponding positions of the coil relative to the field When the coil is vertical at 0° it is moving parallel to the direction of the magnetic field the size of the induced p.d
Is zero
  • Is zero is zero When the coil has rotated by 90° it is now horizontal and moving perpendicular to the direction of the magnetic field the size of the induced p.d

Section 4 of 8Microphones

When tackling
  • When tackling When tackling a question on either of them, make sure you are writing about the right one!
    • The explanation of the loudspeaker is very similar to the explanation of a motor, however direct current is used in a d.c motor and alternating current is used in a loudspeaker or headphone
You need
  • You need You need to learn how both work
When explaining
  • When explaining When explaining how a loudspeaker works remember to refer to the alternating current and the changing magnetic field that it creates.

Section 5 of 8Transformers

1
Fundamental principles, definitions, and physical or chemical laws governing this topic.
2
Key interactions, structural properties, and process dynamics observed in experiments.
3
Quantitative relationships, key formulas, and criteria required by specification mark schemes.

Section 6 of 8Transformer Equations

Transformer Equations
The input
  • The input The input potential difference across the primary coil is 500 V
A) calculate
  • A) calculate a) Calculate the output potential difference across the secondary coil
B) state
  • B) state b) State whether this is a step-up or step-down transformer
The individual
  • The individual The individual loops of wire going around each side of the transformer should be referred to as turns and not coils
P p
  • P p p p s s p p s s s p p s Worked Example A transformer in a travel adapter steps up a 115 V ac mains electricity supply to the 230 V needed for a hair dryer

Section 7 of 8AC & High Voltage Transmission

Core Concept
  • Core Concept Fundamental principles, definitions, and physical or chemical laws governing this topic.
Mechanism & Behavior
  • Mechanism & Behavior Key interactions, structural properties, and process dynamics observed in experiments.
Exam Applications
  • Exam Applications Quantitative relationships, key formulas, and criteria required by specification mark schemes.

Section 8 of 8Exam Checklist & Tips

Specification Mastery Checklist

  • Key Definitions Ensure precise recall of terms and units as required by examination mark schemes.
  • Equations & Formulas Double-check balanced state symbols, subscripts, and SI unit conversions.
  • Common Misconceptions Verify experimental conditions, controls, and comparative trends across groups.
Transformer Golden Equations Physics Standard

Transformer Turns Ratio & Efficiency

Ratio: Vp / Vs = Np / Ns = Is / Ip

  • Step-up reduces grid thermal loss (P = I2R).
  • Laminated core prevents eddy currents.