Magnetic Effect of Electric Current – Short Notes

Magnet is any substance that attracts iron or iron-like substances.

Properties of Magnet

(i) Every magnet has two poles i.e., North and South.
(ii) Like poles repel each other.
(iii)Unlike poles attract each other.
(iv)A freely suspended bar magnet aligns itself in nearly north-south direction, with its north pole towards north direction.

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Magnetic Field: The area around a magnetic in which its magnetic force can be experienced.
• Its SI unit is Tesla (T).
• Magnetic field has both magnitude and direction.
• Magnetic field can be described with help of a magnetic compass.
• The needle of a magnetic compass is a freely suspended bar magnet.

Characteristics of Field Lines

(i) Field lines arise from North pole and end into South pole of the magnet.
(ii) Field lines are closed curves.
(iii)Field lines are closer in stronger magnetic field.
(iv)Field lines never intersect each other as for two lines to intersect, there must be two north directions at a point, which is not possible.
(v) Direction of field lines inside a magnet is from South to North.
(vi) The relative strength of magnetic field is shown by degree of closeness of field lines.

H. C. Oersted was the first person to state that electric current has magnetic field.

Right Hand Thumb Rule

Imagine you are holding a current carrying straight conductor in your right hand such that the thumb is pointing towards the direction of current. Then the fingers wrapped around the conductor give the direction of magnetic field.

Chapter-wise important notes science (Physics) for Board Exams

Magnetic Field Due to Current Through a Straight Conductor

• It can be represented by concentric circles at every point on conductor.
• Direction can be given by right hand thumb rule or compass.
• Circles are closer near the conductor.
• Magnetic field is directly proportional to Strength of current
• Magnetic field is inversely proportional to distance from conductor

Chapter-wise most important science questions for Board Exams

Magnetic Field Due to Current Through a Circular Loop

• 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 is inversely proportional to distance from conductor
• Magnetic field No. of turns in the coil
Magnetic field is additive in nature i.e., magnetic field of one loop adds up to magnetic field of another loop. This is because the current in each circular turn has some direction.

Chapter-wise most important science (Biology) questions for Board Exam

Fleming’s Left Hand Rule

Stretch the thumb, fore finger and middle finger of your left hand such that they are mutually perpendicular. 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.

• Heart and brain in the human body have significant magnetic field.
MRI (Magnetic Resonance Imaging) : Image of internal organs of body can be obtained using magnetic field of the organ.
Galvanometer : Instrument that can detect the presence of current in a circuit. It also detects the direction of current.

Electro Magnetic Induction

When a conductor is placed in a changing magnetic field, some current is induced in it. Such current is called induced current and the phenomenon is called electromagnetic induction.

Fleming’s Right Hand Rule

Hold the thumb, the fore finger and the middle finger of right hand at right angles to each other. If the fore finger is in the direction of magnetic field and the thumb points in the direction of motion of conductor, then the direction of induced current is indicated by
middle finger.

• Working principle of electric generator.
• Used to find direction of induced current.

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 s = I/50 s
Frequency = 1/Time Period = 50 Hz

• A. C. can be transmitted over long distance without much loss of energy.
• A. C. cannot be stored.

Direct Current (D. C.) :

The current which does not reverse its direction.
• D. C. can be stored.
• Loss of energy during transmission over long distance is high.
• Sources of D. C. : Cell, Battery, Storage cells.

Domestic Electric Circuits

• There are three kinds of wires used :
(i) Live wire (positive) with red insulation cover.
(ii) Neutral wire (negative) with black insulation cover.
(iii) 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 accidently.
• Resistance of circuit becomes low.
• Can result in overloading.

Overloading : When current drawn is more than current carrying capacity of a conductor,
it results in overloading.
Causes of overloading :
(i) Accidental hike in voltage supply.
(ii) Use of more than one appliance in a single socket.

Safety devices :
(i) Electric fuse
(ii) Earth wire
(iii)MCB (Miniature Circuit Breaker)

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