Notes For All Chapters Science Class 10 CBSE
1. Introduction
Electric current produces various effects — heating, chemical, and magnetic effects.
A current-carrying conductor behaves like a magnet.
Hans Christian Oersted (1777–1851):
- Discovered in 1820 that a compass needle deflects when a current passes through a nearby conductor.
- Proved that electricity and magnetism are related.
- The unit of magnetic field strength “oersted” is named in his honour.
2. Magnetic Field and Field Lines
Magnetic Field
The region around a magnet where its magnetic force can be detected is called a magnetic field.
A compass needle (a small bar magnet) aligns itself with the magnetic field.
Like poles repel, and unlike poles attract.
Magnetic Field Lines
Lines that represent the direction and strength of a magnetic field.
Demonstrated by sprinkling iron filings around a bar magnet.
Properties of magnetic field lines:
- Originate from north pole and terminate at south pole outside the magnet.
- Inside the magnet, they go from south to north, forming closed loops.
- Closer field lines → stronger magnetic field.
- Field lines never intersect; otherwise, the compass would point in two directions simultaneously.
3. Magnetic Field Due to Current-Carrying Conductor
(A) Straight Conductor
- A current-carrying straight conductor produces a circular magnetic field around it.
- Direction of magnetic field depends on the direction of current.
- Deflection increases with increased current.
- Deflection decreases as the distance from the conductor increases.
Right-Hand Thumb Rule
- Hold the conductor with right hand, thumb pointing in direction of current.
- The direction in which fingers curl represents direction of magnetic field lines.
- Also called Maxwell’s Corkscrew Rule.
4. Magnetic Field Due to Circular Loop
A straight conductor bent into a circular loop produces magnetic field lines that:
- Are concentric circles near the conductor.
- Straighten at the center of the loop.
Magnetic field at the center is the resultant of all field lines in the same direction.
Field ∝ number of turns (n): Magnetic field increases with more turns in the coil.
5. Magnetic Field Due to Solenoid
Solenoid: A coil of many circular turns of insulated copper wire in the shape of a cylinder.
Field lines inside a solenoid are:
- Parallel and straight, indicating a uniform magnetic field.
Solenoid behaves like a bar magnet with north and south poles.
Electromagnet: Soft iron placed inside a solenoid becomes magnetised due to the strong magnetic field.
6. Force on a Current-Carrying Conductor in a Magnetic Field
A conductor carrying current in a magnetic field experiences a force.
Ampere’s Observation: Magnet exerts a force on a conductor and vice versa.
The direction of force depends on:
- Direction of current
- Direction of magnetic field
Force is maximum when current is perpendicular to the magnetic field.
Fleming’s Left-Hand Rule
Stretch the thumb, forefinger, and middle finger of the left hand mutually perpendicular.
- Forefinger → Direction of magnetic field (B)
- Middle finger → Direction of current (I)
- Thumb → Direction of force (F)
Applications: Electric motors, generators, loudspeakers, etc.
7. Domestic Electric Circuits
Supply and Wiring
Domestic power supply: 220 V AC, 50 Hz.
Wires:
- Live wire (red): Positive
- Neutral wire (black): Negative
- Earth wire (green): Safety measure
Working of Domestic Circuit
Supply passes through a meter and main fuse to the main switch.
Two separate circuits:
- 15 A circuit: For heavy appliances (geysers, refrigerators)
- 5 A circuit: For light appliances (bulbs, fans)
Parallel connection ensures equal potential difference across all appliances.
Safety Measures
Earth Wire: Prevents electric shocks by keeping appliance potential at earth level.
Fuse: Prevents damage due to short-circuiting or overloading.
- Short circuit: Live and neutral wires touch each other.
- Overloading: Connecting too many appliances or sudden voltage hike.
8. Magnetism in Medicine
Ion currents in nerve cells produce magnetic fields.
Magnetic fields of the heart and brain are significant.
Magnetic Resonance Imaging (MRI): Used for imaging internal body parts for diagnosis.
9. Important Rules & Laws
| Rule | Use |
|---|---|
| Right-Hand Thumb Rule | Direction of magnetic field around a straight conductor |
| Fleming’s Left-Hand Rule | Direction of force on a current-carrying conductor |
| Maxwell’s Corkscrew Rule | Alternative to right-hand rule for field direction |
Points to Remember
Magnetic field lines never cross each other.
Field strength is greater where lines are closer.
Electromagnet: Soft iron core inside a current-carrying solenoid.
Force on conductor is maximum when current is perpendicular to the field.
Parallel wiring in homes ensures all appliances receive the same voltage.
Fuse and earthing are essential for safety.
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