8th Sci. Chapter 4: Current Electricity and Magnetism Notes.

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✍🏻... विज्ञान विषयाच्या माहितीसाठी खालील⬇️ लिंकला🖇️ स्पर्श करा.

          👉  माहिती विज्ञानाची 🎷

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1. Fundamental Concepts

Atomic Structure: An atom contains equal numbers of positively charged protons and negatively charged electrons, making it electrically neutral overall.

Ex. Atom of sodium 

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Current Electricity: Produced when negatively charged electrons in an electrical conductor are made to flow.

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Electrostatic Potential: The electric level deciding the direction of flow of electric charges. Positive charge tends to flow from a higher electric level to a lower electric level.

Potential Difference (V): The difference between the electrostatic potential of two points.

Unit: Volt (V) in the SI system.

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Flow of current: Electrons flow from the negative terminal to the positive terminal, while conventional current flows in the opposite direction.

Electric Current (I): The amount of electrical charge flowing through a wire in 1 second.

Formula

Electric Current = Charge / Time

I = Q / t

Unit: SI unit is Coulomb / second (C/s). 

or Ampere (A).

Nature Electric Current: Scalar quantity.

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2. Types of Electric Cells

An electric cell maintains a constant potential difference between its two terminals to produce a uniform flow of charges.

Cell Type: Dry Cell 

Components/Structure: Negative Terminal: Zinc (Zn) metal layer

• Positive Terminal: Carbon/Graphite Rod

• Electrolyte: Wet pulp of zinc chloride (ZnCl₂) & ammonium chloride (NH₄Cl)

• Depolarizer: Manganese dioxide (MnO₂) paste 

Key Features • Chemical reaction is slow, so a large current cannot be obtained.

• Longer shelf life, convenient, portable.

Uses: Used in radios, wall clocks, and torches.

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Cell Type: Lead-Acid Cell 

Components/Structure: 

• Positive Terminal: Lead dioxide (PbO₂)

• Negative Terminal: Lead (Pb)

• Electrolyte: Dilute Sulfuric Acid (H₂SO₄)

• Potential Difference: ≈ 2V 

Key Features: 

• Rechargeable after discharge.

• Can deliver large current.

Uses: Used in cars, trucks, motorcycles, and UPS.

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Cell Type: Ni-Cd Cell 

Components/Structure: 

• Portable rechargeable cell

• Potential Difference: 1.2 V

Uses

• Used in portable gadgets required to be carried to different places.

Cell Type: Lithium-ion Cell 

Components/Structure: 

• Modern rechargeable technology 

• Stores more electrical energy compared to Ni-Cd cells.

Uses:

• Used in smartphones, laptops, etc.

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3. Electric Circuits 

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Electric Circuit: A continuous path formed by connecting cells, a load (bulb), a key, and wires through which current flows.

Connecting Cells in Series (Battery):

Connecting the positive terminal of one cell to the negative terminal of the next to obtain a higher overall potential difference.

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Example: If 3 cells of 1 V each are connected in series, total potential difference = 3 V.

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4. Magnetic Effects of Electric Current

Oersted's Discovery: Hans Christian Oersted first observed that when an electric current passes through a wire, a magnetic field is produced around it (a nearby magnetic needle deflects).

Electromagnet:

Created by winding an insulated wire tightly around an iron core (like a screw or nail) and passing an electric current through it.

Magnetism remains only as long as current flows; it vanishes when current stops.

Used in scientific research and heavy machinery.

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5. Application: Electric Bell

Components: Electromagnet (copper wire wound on iron piece), iron strip with striker, contact screw, gong/bell, and key/switch.

Working Process:

• Closing the key completes the circuit, causing current to flow through the coil, turning it into an electromagnet.
• The electromagnet attracts the iron strip, causing the attached striker to hit the gong and produce sound.
• As the strip moves forward, it loses contact with the contact screw, breaking the circuit.
• The electromagnet loses its magnetism, and the iron strip springs back to touch the screw, restoring the circuit.
• The cycle rapidly repeats itself, causing the bell to ring.

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आयुष्य म्हणजे अनुभव,

प्रयोग आणि अपेक्षा यांचे समीकरण आहे.....* 

*कालचा दिवस म्हणजे अनुभव होता...*

 *आजचा दिवस प्रयोग असतो....* 

*आणि उद्याचा दिवस ही अपेक्षा असते....*

 *वाट्याला आलेल आयुष्य मर्यादित आहे, 

अनिश्चित आहे.....*

 *म्हणूनच कसलीही अपेक्षा न ठेवता

 कुणाचही चांगलें करण्याचा प्रयत्न करावा....* 

*कारण एक प्रसिद्ध विधान आहे....

जे लोक नेहमी फुल वाटतात 

त्यांच्या हातांना ही सुगंध दरवळतो....!!*

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