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Sound – Class 9 Science Complete Notes

1. What is Sound? Sound is a form of energy which produces a sensation of hearing in our ears. Sound is produced by vibrating objects. Examples include vibrating tuning fork, vocal cords in humans, bells, musical instruments, etc. Vibration: Rapid to-and-fro (back and forth) motion of an object. Short Question: Can sound be produced without vibration? Answer: No, sound cannot be produced without vibration. 2. Medium of Sound The substance through which sound travels is called a medium . Sound can travel through solids, liquids, and gases but cannot travel through vacuum . Process of Sound Propagation: When an object vibrates, it makes the air particles around it vibrate. These air particles move back and forth from their original (rest) position. The vibrating air particles push nearby air particles. This causes the nearby particles to also start vibrating. In this way, vibrations pass from one particle to another. This process continues through the medi...
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CLASS 10 SCIENCE NOTES CHAPTER - MAGNETIC EFFECTS OF ELECTRIC CURRENT

Magnetic Effects of Electric Current – Class 10 Notes

Magnet

An object which attracts pieces of iron, nickel, and cobalt.

Poles of a Magnet

  • North Pole
  • South Pole

Like poles repel and unlike poles attract.

Magnetic Compass

  • A small magnet in the shape of a needle.
  • Detects presence of a magnet or magnetic field.
  • Deflects more when the magnetic field is stronger.

Magnetic Field (B)

The space around a magnet where magnetic materials experience a force.

It has both magnitude and direction. So, it is a vector quantity.

Direction of Magnetic Field

It is the path along which a free north pole moves.

Magnetic Field Lines

  • Imaginary lines representing the direction of magnetic field.
  • Outside the magnet: N → S
  • Inside the magnet: S → N
  • They are closed curves.
  • Two field lines never intersect.
Reason: If they intersect, the compass needle would point in two directions at a time, which is impossible.

Magnitude of Magnetic Field

  • Closer field lines means stronger magnetic field
  • Far apart field lines means weaker magnetic field

Uniform & Non-uniform Magnetic Field

Uniform field: Field lines are parallel and equidistant.

Non-uniform field: Field lines are unevenly spaced.

Oersted's Discovery

Electric current produces a magnetic field.

Maxwell’s Right-Hand Thumb Rule

If the thumb points in the direction of current, curled fingers give the direction of magnetic field.

Magnetic Field Due to a Straight Current-Carrying Wire

Depends on:

  • Current (i) → More current, stronger field.
  • Distance (d) → More distance, weaker field.
  • Direction of current → Reversing current reverses field.

Magnetic Field Due to Circular Loop

Field lines are circular near the wire but become straight near the center of the loop.

Factors affecting strength:

  • Number of turns
  • Current
  • Radius of loop

Solenoid

A coil with many circular turns of insulated copper wire, wrapped in the form of a cylinder.

Characteristics:

  • Acts like a bar magnet.
  • Has north and south poles.
  • Magnetic field inside is strong and uniform.

Strength depends on:

  • Number of turns
  • Current
  • Gap between turns
  • Material inside the core

Electromagnet

  • A solenoid with a soft iron core.
  • Strong temporary magnet.
  • Polarity can be reversed by reversing current.

Bar Magnet vs Solenoid vs Electromagnet

  • Bar Magnet: Permanent magnet with fixed polarity.
  • Solenoid: Temporary magnet from electric current.
  • Electromagnet: Strong temporary magnet (solenoid + iron core).

Force on Current-Carrying Conductor in Magnetic Field

A conductor experiences force when placed in magnetic field while carrying current.

Fleming’s Left-Hand Rule


According to Fleming's left-hand rule: Hold the forefinger, the centre finger and the thumb of your left hand at right angles to one another . Adjust your hand in such a way that the forefinger points in the direction of magnetic field and the centre finger points in the direction of current, then the direction in which thumb points, gives the direction of force acting on the conductor.

Factors Affecting Force

  • Current
  • Magnetic Field (B)
  • Length of conductor
  • Angle between field and conductor

Domestic Electric Circuits

Earthing

Prevents electric shocks by sending excess current to the ground.

Short Circuit & Overloading

Excess current causes heating and may damage appliances or cause fire.

Electric Fuse

  • Made of tin-plated copper (low melting point).
  • Melts during heavy current and protects appliances.

15A fuse: geyser, iron, toaster

5A fuse: bulbs, fans

AC vs DC

Description D.C. Direct Current A.C. Alternating Current
Direction Do not change its direction Changes its direction
Source Obtained from cell battery Obtained from Electric Power Plants with A.C. Generators
Interaction Repulsive Attractive
Voltage Change Voltage can not be changed Voltage can be changed (via transformers)
Power Loss More power loss over long transmission Less Power loss over long transmission

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