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Electricity and Magnetism - Electromagnetic effects (Motor effect and electromagnetic induction)

Grade 11IGCSEPhysics

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Motor Effect: When a current-carrying conductor is placed in a magnetic field, it experiences a force FF. This occurs because the magnetic field of the current interacts with the external magnetic field.

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Fleming's Left-Hand Rule: Used to find the direction of the force in motors. Thumb = Force (FF), First finger = Magnetic Field (BB from NN to SS), Second finger = Current (II from ++ to −-).

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Electromagnetic Induction: The process of generating an electromotive force (EMF) in a conductor when it experiences a changing magnetic field or 'cuts' through magnetic field lines.

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Faraday's Law: The magnitude of the induced EMF is directly proportional to the rate at which the conductor cuts magnetic field lines.

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Lenz's Law: The direction of an induced current is such that it opposes the change that created it. This is a consequence of the principle of conservation of energy.

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Fleming's Right-Hand Rule: Used for generators/induction. Thumb = Motion/Force, First finger = Field (BB), Second finger = Induced Current (II).

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Transformers: Devices that change the voltage of an alternating current (ACAC). A step-up transformer increases voltage (Ns>NpN_s > N_p), while a step-down transformer decreases it (Ns<NpN_s < N_p).

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The Soft Iron Core: Used in transformers to concentrate the magnetic field lines and ensure maximum flux linkage between the primary and secondary coils.

📐Formulae

VpIp=VsIsV_p I_p = V_s I_s

\frac{V_p}{V_s} = rac{N_p}{N_s}

P=I2RP = I^2 R

P=IVP = IV

💡Examples

Problem 1:

A transformer has 200200 turns on its primary coil and 50005000 turns on its secondary coil. If an input voltage of 230 V230\text{ V} ACAC is applied to the primary coil, calculate the output voltage.

Solution:

Vs=Vp×NsNp=230×5000200=5750 VV_s = \frac{V_p \times N_s}{N_p} = \frac{230 \times 5000}{200} = 5750\text{ V}

Explanation:

Using the transformer turns ratio formula VpVs=NpNs\frac{V_p}{V_s} = \frac{N_p}{N_s}, we rearrange to solve for the secondary voltage VsV_s.

Problem 2:

A power line with a resistance of 0.5 Ω0.5\text{ }\Omega carries a current of 20 A20\text{ A}. Calculate the power loss in the cable.

Solution:

Ploss=I2R=(20)2×0.5=400×0.5=200 WP_{loss} = I^2 R = (20)^2 \times 0.5 = 400 \times 0.5 = 200\text{ W}

Explanation:

Power loss in transmission lines is primarily due to heating, calculated using the formula P=I2RP = I^2 R.

Problem 3:

State two ways to increase the magnitude of the induced EMF in an ACAC generator.

Solution:

  1. Increase the speed of rotation of the coil.
  2. Increase the number of turns on the coil.

Explanation:

According to Faraday's Law, increasing the rate of cutting magnetic flux (speed) or increasing the total flux linkage (turns) results in a higher induced EMF.

Electromagnetic effects (Motor effect and electromagnetic induction) Revision - Grade 11 Physics…