Here I am going to provide you CBSE Class 10 Science Chapter 13 Magnetic Effects of Electric Current. By going through Magnetic Effects of Electric Current Class 10 Notes you can revise the Magnetic Effects of Electric Current Chapter in a very effective way. I hope that this will certainly help you in your studies!
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Magnet
- A magnet is a material that produces a field that attracts or repels other such materials of magnetic nature.
- Lodestone is a naturally occurring magnet. It attracts materials like Iron, Nickel, Cobalt, etc.
Properties of Magnet
- A magnet is always bipolar with poles named north and south poles. These two poles always exist together and can not be separated.
- North pole of a magnet is the side which points to Earth’s geographic north when it is freely suspended.
- Similar to charges, poles attract and repel. Like poles repel while unlike poles attract each other.
Magnetic field
- The region around a magnet where its magnetic influence can be experienced is called a magnetic field.
- The direction and strength of a magnetic field are represented by magnetic lines of force.
Magnetic field lines
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- Magnet’s magnetic field lines result in the formation of continuous/running closed loops.
- The tangent to the field line at any given point indicates the direction of the total magnetic field at that point.
- The greater the number of field lines crossing per unit area, the higher the intensity, the stronger the magnitude of the magnetic field.
- There is no intersection between the magnetic field lines.
Why do Magnetic Field Lines do not intersect?
Magnetic field lines do not intersect as there will be two tangential magnetic field directions associated with the same point, which does not occur. If a compass needle is placed at that point, it will show two different directions of the magnetic field which is absurd.
Oersted’s experiment
- When electric current flows through a current carrying conductor, it produces a magnetic field around it.
- This can be seen with the help of a magnetic needle which shows deflection.
- The more the current, the higher the deflection.
- If the direction of current is reversed, the direction of deflection is also reversed.
Electromagnetism and electromagnet
- An electromagnet is an artificial magnet which produces a magnetic field on the passage of electric current through a conductor.
- This field disappears when the current is turned off.
- The phenomenon of producing or inducing a magnetic field due to the passage of electric current is called electromagnetism.
Magnetic field due to a straight current carrying conductor
- When current is passed through a straight current-carrying conductor, a magnetic field is produced around it.
- Using the iron filings, we can observe that they align themselves in concentric circles around the conductor.
- Direction can be given by right hand thumb rule or compass.
- Circles are closer near the conductor.
- Magnetic field ∝ Strength of current.
- Magnetic field ∝ 1/Distance from conductor
Right-hand thumb rule
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If a straight conductor is held in the right hand in such a way that the thumb points along the direction of the current, then the tips of the fingers or the curl of the fingers show the direction of magnetic field around it.
Magnetic field due to current through a circular loop
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- It can be represented by concentric circle at every point.
- Circles become larger and larger as we move away.
- Every point on wire carrying current would give rise to magnetic field appearing as straight line at centre of the loop.
- The direction of magnetic field inside the loop is same.
Factors affecting magnetic field of a circular current carrying conductor
- Magnetic field ∝ Current passing through the conductor
- Magnetic field∝ 1/Distance from conductor
- Magnetic field ∝ No. of turns in the coil
Magnetic field due to current in a solenoid
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- A solenoid is a coil of many circular windings wrapped in the shape of a cylinder.
- When current is passed through it, it behaves similar to a bar magnet, producing a very similar field pattern as that of a bar magnet.
- To increase the strength a soft iron core is used.
Direction of Magnetic Field
Outside the solenoid: North to South
Inside the solenoid: South to North
Difference between Electromagnet and Permanent Magnet
Electromagnet
- It is a temporary magnet, so, can be easily demagnetised.
- Strength can be varied.
- Polarity can be reversed.
- Generally strong magnet.
Permanent Magnet
- Can not be easily demagnetised.
- Strength is fixed.
- Polarity cannot be reversed.
- Generally weak magnet.
Force on a Current Carrying Conductor in a Magnetic Field
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- Ampere’s experiment states that when an electric conductor is placed in a magnetic field, it experiences a force.
- This force is directly proportional to the current and is also perpendicular to its length and magnetic field.
- Force on a straight current carrying conductor is mutually perpendicular to the magnetic field and the direction of the current.
Fleming’s left-hand rule
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- Fleming’s left hand rule states that when we stretch the thumb, fore finger and middle finger of our left hand such that they are mutually perpendicular.
- Then if fore finger points in the direction of magnetic field, middle finger in the direction of current then thumb will point in the direction of motion or force.
Electric motor
- Electric Motor converts electrical energy into mechanical energy.
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- An electric motor consists of a rectangular coil ABCD of insulated copper wire. The coil is placed between the two poles of a magnetic field such that the arm AB and CD are perpendicular to the direction of the magnetic field.
- The ends of the coil are connected to the two halves P and Q of a split ring. The inner sides of these halves are insulated and attached to an axle.
- The external conducting edges of P and Q touch two conducting stationary brushes X and Y, respectively.
- Current in the coil ABCD enters from the source battery through conducting brush X and flows back to the battery through brush Y.
- The force acting on arm AB pushes it downwards while the force acting on arm CD pushes it upwards.
- Thus the coil and the axle O, mounted free to turn about an axis, rotate anti-clockwise.
- At half rotation, Q makes contact with the brush X and P with brush Y. Therefore the current in the coil gets reversed and flows along the path DCBA.
- The split ring acts as a commutator which reverse the direction of current and also reverses the direction of force acting on the two arms AB and CD.
- Thus the arm AB of the coil that was earlier pushed down is now pushed up and the arm CD previously pushed up is now pushed down.
- Therefore the coil and the axle rotate half a turn more in the same direction. The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil and to the axle.
- Commutator: A device that reverses the direction of flow of current through a circuit is called a commutator.
- Armature: The soft iron core, on which the coil is wound including the coils is called armature. It enhances the power of the motor.
Faraday’s experiment
- Faraday discovered that a magnetic field interacts with an electric circuit by inducing a voltage known as EMF (electromotive force) by electromagnetic induction.
- Moving a magnet towards a coil sets up a current in the coil circuit, as indicated by deflection in the galvanometer needle.
Electromagnetic induction
- The phenomenon of electromagnetic induction is the production of induced EMF and thereby current in a coil, due to the varying magnetic field with time.
- If a coil is placed near a current-carrying conductor, the magnetic field changes due to a change in I or due to the relative motion between the coil and conductor.
- The direction of the induced current is given by Fleming’s right-hand rule.
Fleming’s right-hand rule
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If the thumb indicates the direction of the movement of conductor, fore-finger indicating direction of the magnetic field, then the middle finger indicates direction of the induced current.
Difference between Fleming's Left Hand and Left Hand Rule
Electric generator
- The device that converts mechanical energy into electrical energy.
- Operates on the principle of electromagnetic induction.
- An electric generator consists of a rotating rectangular coil ABCD placed between the two poles of a permanent magnet.
- The two ends of this coil are connected to the two rings R1 and R2. The inner side of these rings are made insulated.
- The inner side of these rings are made insulated. The two conducting stationary brushes B1 and B2 are kept pressed separately on the rings R1 and R2, respectively.
- The two rings R1 and R2 are internally attached to an axle. The axle may be mechanically rotated from outside to rotate the coil inside the magnetic field.
- Outer ends of the two brushes are connected to the galvanometer to show the flow of current in the given external circuit.
- When the axle attached to the two rings is rotated such that the arm AB moves up (and the arm CD moves down) in the magnetic field produced by the permanent magnet.
- After half a rotation, arm CD starts moving up and AB moving down. As a result, the directions of the induced currents in both the arms change, giving rise to the net induced current in the direction DCBA.
- The current in the external circuit now flows from B1 to B2. Thus after every half rotation the polarity of the current in the respective arms changes.
- To get a direct current (DC), a split-ring type commutator must be used. With this arrangement, one brush is at all times in contact with the arm moving up in the field, while the other is in contact with the arm moving down.
- The direct current always flows in one direction, whereas the alternating current reverses its direction periodically.
Alternate Current (A.C.)
- The current which reverses its direction periodically.
- In India, A.C. reverses its direction in every 1/100 second.
- Time period = 1/100 + 1/100 = 1/50 s
- Frequency = 1/time period = 1/50 = 50 Hz
Advantage of A.C.
- A.C. can be transmitted over long distance without much loss of energy.
Disadvantage of A.C.
- A.C. cannot be stored.
Direct Current (D.C.)
- The current which does not reverse its direction.
Advantage of D.C.
- D.C. can be stored.
Disadvantage of D.C.
- Loss of energy during transmission over long distance is high.
Domestic Electric Circuits
- Live wire (positive) with red insulation cover.
- Neutral wire (negative) with black insulation cover.
- Earth wire with green insulation cover.
- The potential difference between live and neutral wire in India is 220 V.
- Pole ⇒ Main supply ⇒ Fuse ⇒ Electricity meter ⇒ Distribution box ⇒ To separate circuits.
- Earth Wire: Protects us from electric shock in case of leakage of current especially in metallic body appliances. It provides a low resistance path for current in case of leakage of current.
- Short Circuit: When live wire comes in direct contact with neutral wire accidentally. The resistance of circuit becomes low which can result in overloading.
- Overloading: When current drawn is more than current carrying capacity of a conductor, it results in overloading.
Causes of overloading
- Accidental hike in voltage supply.
- Use of more than one appliance in a single socket.
Fuse
- Fuse is a protective device in an electrical circuit in times of overloading.
- Overloading is caused when the neutral and live wire come in contact due to damage to the insulation or a fault in the line.
- In times of overloading the current in circuit increases (short circuit) and becomes hazardous. Joule’s heating (resistive or ohmic heating on the passage of current) in the fuse device melts the circuit and breaks the flow of current in the circuit.