Difference between revisions of "Electromagnetic induction"

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#''[[Increasing the speed of the relative motion between the coil and the magnet]]'' – If the same coil of wire passed through the same magnetic field but its speed or velocity is increased, the wire will cut the lines of flux at a faster rate so more induced emf would be produced.
 
#''[[Increasing the speed of the relative motion between the coil and the magnet]]'' – If the same coil of wire passed through the same magnetic field but its speed or velocity is increased, the wire will cut the lines of flux at a faster rate so more induced emf would be produced.
 
#''[[Increasing the strength of the magnetic field]]'' – If the same coil of wire is moved at the same speed through a stronger magnetic field, there will be more emf produced because there are more lines of force to cut.
 
#''[[Increasing the strength of the magnetic field]]'' – If the same coil of wire is moved at the same speed through a stronger magnetic field, there will be more emf produced because there are more lines of force to cut.
 +
Factors affecting the magnitude of induced emf:
 +
The magnitude of induced emf is equal to the rate of change of magnetic flux i.e.,
 +
Induced emf= (Change in magetic flux)/(Time in which the magentic flux changes)
 +
i) the change in the magnetic flux and
 +
ii) the time in which the magnetic flux changes.
 +
 +
 +
Difference between A.C. and D.C
 +
Direct current (D.C.) Alternating current (A.C.)
 +
1. It is the current of constant magnitude.
 +
2. It flows in one direction in the circuit.
 +
3. It is obtained from a cell (or battery) 1. It is the current of magnitude varying with time.
 +
2. It reverses its direction periodically while flowing in a circuit.
 +
3. It is obtained from A.C. generator and mains.
 +
 +
Advantages of A.C. over D.C.:
 +
In India, we use 220 volt a.c. in our houses and factories. The use of A.C. is advantageous over D.C. because the voltage of A.C. can be stepped up by the use of a step-up transformer at the power generating station before transmitting it over the long distances. It reduces the loss of electric energy as heat in the transmission line wires. The A.C. is then stepped down to 220 volt by the use of step-down transformers at the successive sub-stations before supplying it to the houses or factories. If D.C. is generated at the power generating station, its voltage cannot be increased for transmission and so due to passage of high current in the transmission line wires; there will be a huge loses of electrical energy as heat in the line wires.
 +
 +
A.C. Generator D.C. Motor
 +
1. A generator is a device which converts mechanical energy into electrical energy.
 +
2. A generator works on the principle of electrro magnetic inductions.
 +
3. In a generator, the coil is rotated in a magnetic field so as to produce electric current.
 +
4. A generator makes use of two separate coaxial slip rings. 1. A d.c. motor is a device which converts electrical energy into mechanical energy.
 +
A d.c. motor works on the principle of force acting on a current carrying conductor placed in a magnetic field.
 +
3. In d.c. motor, the current from d.c. source flows in the coil placed in a magnetic field due to which the coil rotates.
 +
4. A d.c. motor makes use of two parts of slip ring (i.e., split rings) which act as a commutatar. 
 +
 +
Applications of electromagnetic induction:
 +
Transformer:
 +
In our daily life, we use various electrical applications which require working voltage different form the mains voltage (i.e., 220V) e.g. a door bell needs 6V while a television needs several 1000V. To provide suitable voltage to different applications from the mains, we use transformers with them. Thus, Transformer is a device by which the amplitude of an alternating e.m.f. can be increased or decreased.
 +
A transformer does not affect the frequency of the alternating voltage. The frequency remains unchanged (=50hz)
 +
Principal :  A transformer works on the principle of electromagnetic induction and make use of two coils having different number of turns. The alternating e.m.f. to be altered is applied across one coil. Which there is change of magnetic field line due to varying current in this coil the magnetic field line linked with the other coil also changes and so an induced varying current of the same frequency, but of different magnitude flows in the other coil. 
 +
Construction : A transformer consists of a rectangular soft iron core made up from the thin laminated sheets of soft iron of T and U shape, placed alternately one above the other and insulated from each other by a paint (or varnish) coating over them as shown in the fig. so as to behave like a simple rectangular core.
 +
The laminated core prevents the loss of energy due to eddy currents in the core.
 +
On one arm of the core, a coil P of insulated copper wire is wound. This coil is connected with the source of alternating e.m.f. (i.e., at the ends of the this coil, the input is given). This is called primary coil.
 +
One the other arm of the core, another coil S of insulated copper wire is wound. The induced alternating e.m.f is obtained across the terminals of this coil (i.e., output is obtained at the ends of this coil). This is called the secondary coil. The ratio of number of turns Ns in secondary coil to the number of turns Np in primary coil (i.e., Ns/Sp) is called the turns ratio.
 +
i.e.,Turns ratio n= (Number of turns in secondary coil Ns)/(Number of turns in primary coil Np)
 +
                         
 +
The advantage of using a closed core is that it gives a closed path for the magnetic field lines and therefore almost all the magnetic field lines caused due to current in the primary coil, remain linked with the secondary coil (i.e., the flux linkage is nearly perfect) and loss of energy is avoided. The core is made of soft iron so that hysteresis loss of energy in the core is less.
 +
 +
Working : When the terminals of primary coil are connected to the source of alternating e.m.f., a varying current flows through the primary coil. This varying current produces a varying magnetic field in the core of transformer. Thus the magnetic field lines linked with the secondary coil vary. The change of magnetic field line through the secondary coil induces an emf in it. The induced emf varies in the same manner as the applied emf in the primary coil varies and thus has the same frequency as that of the applied emf.
 +
The magnitude of emf induced in the secondary coil depends on the following two factors.
 +
(i) the ration of the number of turns in the secondary coil to the number of turns in the primary coil (i.e., turns ratio) and
 +
(ii) the magnitude of emf applied in the primary coil
 +
For a transformer,
 +
(emf across the secondary coil (Vs))/(emf across the primary coil (Vp))= (Number of turns in the secondary coil (Ns))/(Number of turns in the primary coil (Np))
 +
 +
((Vs))/( (Vp) )=((Ns))/((Np) )=  is called Turns ratio 'n^' of transformer
 +
 +
The relation between current and voltage of primary and secondary coils of a transformer can be expressed as
 +
((Vs))/( (Vp))= Ip/Is  or IpVp=IsVs
 +
 +
Current x Voltage of primary coil = current x voltage in secondary coil
 +
Types of transformers : 1) Step up transformer : The transformer used to change a low voltage alternating emf to a high voltage alternating emf (of same frequency) is called step-up transformer. In a step-up transformer, the number of turns in the secondary coil are more than the number of tunrs in the primary coil. i.e., turns ratio n>1 or Ns/Np>1. Vs>Vp, but Is<Ip. More current flows in the primary coil. Therefore one must use thicker wire in the primary coil as compared to that in the secondary coil.
 +
2) Step down transformer : The transformer used to change a high voltage alternating emf to a low voltage alternating emf (of same frequency) is called step-down transformer. In a step-down transformer, the numbers of turns in the secondary coil are less than the number of tunrs in the primary coil. i.e., turns ratio n<1 or Ns/Np<1. Vs<Vp, but Is>Ip. Here the secondary winding will require thicker wire due to high current. The use of thicker wire reduces its resistance and therefore reduces the loss of energy as heat in the coil. This energy loss due to heat is known as copper loss.
 +
Uses of Transformaers : i) Use of setp-up transforemer :
 +
a) In transmission of electric power at the power generating station to step up the voltage.b) with television c) with wireless sets and
 +
d) with X-ray tubes to provide a high accelerating voltage.
 +
ii) Use of setp-down transforemer :
 +
a) With electric bells, night electric bulbs, mobile phone, computers, etc.
 +
b) At the power sub-stations to step-down the voltage before its distribution to the consumers.
 +
Induction coil :
 +
You know that for discharge tube experiment high voltage is required. How to produce high voltage from a low voltage DC source? An induction coil is a device for obtaining a very high DC voltage starting from a low DC voltage. An induction coil consists of few turns of a primary coil ‘P’, of thick insulated copper wire wound over a soft iron core connected to a  battery. S is a secondary coil of large number of turns wound over the primary coil. M is a make and break arrangement. When the DC current flows in the primary, ‘C’ gets magnetised. The iron head H of the switch M is attracted towards C so, the circuit breaks and the current in primary stops. C gets demagnetised and H comes back. The process repeats. During make and break circuit, large emf is induced in the secondary. The voltage depends on the turns ratio. Since the number of turns in secondary is very large, a large voltage in produced in the secondary.
 +
While using it remembers that the coil should be in the north and south direction. That means the needle and the coil should be parallel to each other.
 +
 
''These are short notes that the teacher wants to share about the concept, any locally relevant information, specific instructions on what kind of methodology used and common misconceptions/mistakes.''
 
''These are short notes that the teacher wants to share about the concept, any locally relevant information, specific instructions on what kind of methodology used and common misconceptions/mistakes.''
 +
 
===Activity No # 1- '''Properties of Magnets'''===
 
===Activity No # 1- '''Properties of Magnets'''===
 
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{| style="height:10px; float:right; align:center;"

Revision as of 15:18, 24 August 2014

Concept Map

Error: Mind Map file Electromagnetic induction.mm not found



Textbook

  1. Tenth Standart Science Textbook

Additional information

Useful websites

  1. http://en.wikipedia.org/wiki/Electromagnetic_induction
  2. http://www.youtube.com/watch?v=vwIdZjjd8fo
  3. http://www.electronics-tutorials.ws/electromagnetism/electromagnetic-induction.html
  4. https://www.google.co.in/search?q=electromagnetic+induction&oq=Ele&aqs=chrome.0.69i59l2j69i57j0l3.1895j0j8&sourceid=chrome&es_sm=93&ie=UTF-8

Reference Books

  1. Tenth Standard Ready Lesson CD from Education Department – Science Subject

Teaching Outlines

Concept #1 Electro magnetic Induction

Learning objectives

  1. Recall the the properties of magnets
  2. Electromagnetic effect
  3. How emf induced
  4. Emf depends upon the number of turns and speed of the magnet
  5. Michel Faraday experiment

Notes for teachers

Electromagnetic Induction The magnetic flux developed around the coil being proportional to the amount of current flowing in the coils windings as shown.
Electromagnetism coiled wire.gifMicheal Farady.jpg

If additional layers of wire are wound upon the same coil with the same current flowing through them, the static magnetic field strength would be increased.

Therefore, the Magnetic Field Strength of a coil is determined by the ampere turns of the coil. With more turns of wire within the coil the greater will be the strength of the static magnetic field around it.

But what if we reversed this idea by disconnecting the electrical current from the coil and instead of a hollow core we placed a bar magnet inside the core of the coil of wire. By moving this bar magnet “in” and “out” of the coil a current would be induced into the coil by the physical movement of the magnetic flux inside it.

Electromagnetic Induction was first discovered way back in the 1830’s by Michael Faraday. Faraday noticed that when he moved a permanent magnet in and out of a coil or a single loop of wire it induced an ElectroMotive Force or emf, in other words a Voltage, and therefore a current was produced.

Faraday’s Law of Induction

  1. Increasing the number of turns of wire in the coil – By increasing the amount of individual conductors cutting through the magnetic field, the amount of induced emf produced will be the sum of all the individual loops of the coil, so if there are 20 turns in the coil there will be 20 times more induced emf than in one piece of wire.
  2. Increasing the speed of the relative motion between the coil and the magnet – If the same coil of wire passed through the same magnetic field but its speed or velocity is increased, the wire will cut the lines of flux at a faster rate so more induced emf would be produced.
  3. Increasing the strength of the magnetic field – If the same coil of wire is moved at the same speed through a stronger magnetic field, there will be more emf produced because there are more lines of force to cut.

Factors affecting the magnitude of induced emf: The magnitude of induced emf is equal to the rate of change of magnetic flux i.e., Induced emf= (Change in magetic flux)/(Time in which the magentic flux changes) i) the change in the magnetic flux and ii) the time in which the magnetic flux changes.


Difference between A.C. and D.C Direct current (D.C.) Alternating current (A.C.) 1. It is the current of constant magnitude. 2. It flows in one direction in the circuit. 3. It is obtained from a cell (or battery) 1. It is the current of magnitude varying with time. 2. It reverses its direction periodically while flowing in a circuit. 3. It is obtained from A.C. generator and mains.

Advantages of A.C. over D.C.: In India, we use 220 volt a.c. in our houses and factories. The use of A.C. is advantageous over D.C. because the voltage of A.C. can be stepped up by the use of a step-up transformer at the power generating station before transmitting it over the long distances. It reduces the loss of electric energy as heat in the transmission line wires. The A.C. is then stepped down to 220 volt by the use of step-down transformers at the successive sub-stations before supplying it to the houses or factories. If D.C. is generated at the power generating station, its voltage cannot be increased for transmission and so due to passage of high current in the transmission line wires; there will be a huge loses of electrical energy as heat in the line wires.

A.C. Generator D.C. Motor 1. A generator is a device which converts mechanical energy into electrical energy. 2. A generator works on the principle of electrro magnetic inductions. 3. In a generator, the coil is rotated in a magnetic field so as to produce electric current. 4. A generator makes use of two separate coaxial slip rings. 1. A d.c. motor is a device which converts electrical energy into mechanical energy. A d.c. motor works on the principle of force acting on a current carrying conductor placed in a magnetic field. 3. In d.c. motor, the current from d.c. source flows in the coil placed in a magnetic field due to which the coil rotates. 4. A d.c. motor makes use of two parts of slip ring (i.e., split rings) which act as a commutatar.

Applications of electromagnetic induction: Transformer: In our daily life, we use various electrical applications which require working voltage different form the mains voltage (i.e., 220V) e.g. a door bell needs 6V while a television needs several 1000V. To provide suitable voltage to different applications from the mains, we use transformers with them. Thus, Transformer is a device by which the amplitude of an alternating e.m.f. can be increased or decreased. A transformer does not affect the frequency of the alternating voltage. The frequency remains unchanged (=50hz) Principal : A transformer works on the principle of electromagnetic induction and make use of two coils having different number of turns. The alternating e.m.f. to be altered is applied across one coil. Which there is change of magnetic field line due to varying current in this coil the magnetic field line linked with the other coil also changes and so an induced varying current of the same frequency, but of different magnitude flows in the other coil. Construction : A transformer consists of a rectangular soft iron core made up from the thin laminated sheets of soft iron of T and U shape, placed alternately one above the other and insulated from each other by a paint (or varnish) coating over them as shown in the fig. so as to behave like a simple rectangular core. The laminated core prevents the loss of energy due to eddy currents in the core. On one arm of the core, a coil P of insulated copper wire is wound. This coil is connected with the source of alternating e.m.f. (i.e., at the ends of the this coil, the input is given). This is called primary coil. One the other arm of the core, another coil S of insulated copper wire is wound. The induced alternating e.m.f is obtained across the terminals of this coil (i.e., output is obtained at the ends of this coil). This is called the secondary coil. The ratio of number of turns Ns in secondary coil to the number of turns Np in primary coil (i.e., Ns/Sp) is called the turns ratio. i.e.,Turns ratio n= (Number of turns in secondary coil Ns)/(Number of turns in primary coil Np)

The advantage of using a closed core is that it gives a closed path for the magnetic field lines and therefore almost all the magnetic field lines caused due to current in the primary coil, remain linked with the secondary coil (i.e., the flux linkage is nearly perfect) and loss of energy is avoided. The core is made of soft iron so that hysteresis loss of energy in the core is less.

Working : When the terminals of primary coil are connected to the source of alternating e.m.f., a varying current flows through the primary coil. This varying current produces a varying magnetic field in the core of transformer. Thus the magnetic field lines linked with the secondary coil vary. The change of magnetic field line through the secondary coil induces an emf in it. The induced emf varies in the same manner as the applied emf in the primary coil varies and thus has the same frequency as that of the applied emf. The magnitude of emf induced in the secondary coil depends on the following two factors. (i) the ration of the number of turns in the secondary coil to the number of turns in the primary coil (i.e., turns ratio) and (ii) the magnitude of emf applied in the primary coil For a transformer, (emf across the secondary coil (Vs))/(emf across the primary coil (Vp))= (Number of turns in the secondary coil (Ns))/(Number of turns in the primary coil (Np))

((Vs))/( (Vp) )=((Ns))/((Np) )= is called Turns ratio 'n^' of transformer

The relation between current and voltage of primary and secondary coils of a transformer can be expressed as ((Vs))/( (Vp))= Ip/Is or IpVp=IsVs

Current x Voltage of primary coil = current x voltage in secondary coil Types of transformers : 1) Step up transformer : The transformer used to change a low voltage alternating emf to a high voltage alternating emf (of same frequency) is called step-up transformer. In a step-up transformer, the number of turns in the secondary coil are more than the number of tunrs in the primary coil. i.e., turns ratio n>1 or Ns/Np>1. Vs>Vp, but Is<Ip. More current flows in the primary coil. Therefore one must use thicker wire in the primary coil as compared to that in the secondary coil. 2) Step down transformer : The transformer used to change a high voltage alternating emf to a low voltage alternating emf (of same frequency) is called step-down transformer. In a step-down transformer, the numbers of turns in the secondary coil are less than the number of tunrs in the primary coil. i.e., turns ratio n<1 or Ns/Np<1. Vs<Vp, but Is>Ip. Here the secondary winding will require thicker wire due to high current. The use of thicker wire reduces its resistance and therefore reduces the loss of energy as heat in the coil. This energy loss due to heat is known as copper loss. Uses of Transformaers : i) Use of setp-up transforemer : a) In transmission of electric power at the power generating station to step up the voltage.b) with television c) with wireless sets and d) with X-ray tubes to provide a high accelerating voltage. ii) Use of setp-down transforemer : a) With electric bells, night electric bulbs, mobile phone, computers, etc. b) At the power sub-stations to step-down the voltage before its distribution to the consumers. Induction coil : You know that for discharge tube experiment high voltage is required. How to produce high voltage from a low voltage DC source? An induction coil is a device for obtaining a very high DC voltage starting from a low DC voltage. An induction coil consists of few turns of a primary coil ‘P’, of thick insulated copper wire wound over a soft iron core connected to a battery. S is a secondary coil of large number of turns wound over the primary coil. M is a make and break arrangement. When the DC current flows in the primary, ‘C’ gets magnetised. The iron head H of the switch M is attracted towards C so, the circuit breaks and the current in primary stops. C gets demagnetised and H comes back. The process repeats. During make and break circuit, large emf is induced in the secondary. The voltage depends on the turns ratio. Since the number of turns in secondary is very large, a large voltage in produced in the secondary. While using it remembers that the coil should be in the north and south direction. That means the needle and the coil should be parallel to each other.

These are short notes that the teacher wants to share about the concept, any locally relevant information, specific instructions on what kind of methodology used and common misconceptions/mistakes.

Activity No # 1- Properties of Magnets

  • Estimated Time

20 minute

  • Materials/ Resources needed
  1. Magnets
  2. Magnetic needles with stand
  • Prerequisites/Instructions, if any
  • Multimedia resources

Goto Magnet & electromagnets simulations
Magnet&electromagnet.png

  • Website interactives/ links/ simulations
  • Process (How to do the activity)

Give the magnets to students and check the properties of magnets. Ask the students properties of magnets. Give the inst Ask magnetic lines of force using phet tool of magnets and electromagnet.
Give two magnets and a magnetic needle to students group (4-5students). Tell check the properties of magnets

  • Developmental Questions (What discussion questions)
  • Evaluation (Questions for assessment of the child)

1.If a magnetic needle placed along the north and south pole of a bar magnet as shown in the figure, what is the polarity of the a b c and d. mark 2 Magnet3.jpg

  • Pole of a ________ *pole of b _______
  • Pole of c _________ *Pole of d _________
  • Question Corner

To link back to the topic page Goto SCIENCE TOPIC page

Activity No # 2- Electromagnet Experiment

  • Estimated Time
  • Materials/ Resources needed
  1. A strong bar magnet
  2. Copper coil with 500 turns
  3. Galvanometer
  • Prerequisites/Instructions, if any
  • Multimedia resources
  • Website interactives/ links/ simulations
  • Process (How to do the activity)

Show the connection of copper coil and galvanometer.

  • Developmental Questions (What discussion questions)
  • Evaluation (Questions for assessment of the child)
  • Question Corner

Activity No # 3- Electromagnetic Induction using Galvanometer

  • Estimated Time
  • Materials/ Resources needed
  • Prerequisites/Instructions, if any
  • Multimedia resources
  • Website interactives/ links/ simulations
  • Process (How to do the activity)

Show the electromagnetic induction using galvanometer and copper coil. Observe the changes of galvanometer deflections.

  • Developmental Questions (What discussion questions)
  • Evaluation (Questions for assessment of the child)

1.The device that detects the induced emf is called _________________ mark 1

2.Which the following emf is produced? Yes/no
a) Coil is steady, magnet is moved inside the coil _______________
b) Coil and magnet are moved away in opposite direction _______________
c) Magnet is steady, Coil is moved towards magnet ____________
d) Coil and magnet both are moved together __________________ mark 2

3.copper coil is connected to Galvanometer and a bar magnet. What are the changes in the following

  • Magnet kept inside the coil ____________________________
  • Magnet is pushed slowly ________________________________
  • Magnet is pushed inside the coil very quickly _____________________ mark 2
  • Question Corner

Activity No # 4- Factors influences emf

  • Estimated Time
  • Materials/ Resources needed
  • Prerequisites/Instructions, if any
  • Multimedia resources
  • Website interactives/ links/ simulations

http://www.youtube.com/watch?v=vwIdZjjd8fo

  • Process (How to do the activity)

Show the short video of number of coils increasing emf is increasing.

  • Developmental Questions (What discussion questions)
  • Evaluation (Questions for assessment of the child)

1. Which the following coil is more emf produced when magnet movement inside the coil? mark 1
Coil1.png
2. A copper coil, a strong bar magnet and a led bulb are on the table. How do you glow on the led bulb? Mark 2

  • Question Corner

Activity No # 5- Michel Faraday Experiment

  • Estimated Time
  • Materials/ Resources needed
  • Prerequisites/Instructions, if any
  • Multimedia resources
  • Website interactives/ links/ simulations
  • Process (How to do the activity)

Show the video of Michel Faraday experiment.

  • Developmental Questions (What discussion questions)
  • Evaluation (Questions for assessment of the child)
  • Question Corner

To link back to the topic page Give the link of the page name from where activity was given Back


Concept #2 -

Learning objectives

Notes for teachers

Activities

Concept #3 -

Learning objectives

Notes for teachers

Activities

  1. Activity 1 -

Concept #4

Learning objectives

Notes for teachers

Activities

Project Ideas

Fun corner

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