Урок 145 (осн). Действия электрического тока

Scientific concepts / nature phenomena presented

Electric current (definition)

• Electric current is the ordered (directed) movement of charged particles.
• Charge carriers can be:
  • Electrons in metals
  • Ions in liquids and gases

Actions (effects) of electric current

The effects of current on substances and the environment are grouped into several “actions”.

1) Thermal action (heating effect)

• Phenomenon: When current flows through a conductor, the conductor heats up.

• Underlying causal chain (as explained):

  • current flows → wire heats → wire expands → wire sags/deflects

• Examples / applications:

  • Electric heaters: electric stoves, soldering irons, electric ovens
  • Incandescent lamps: heating a tungsten filament until it glows
  • Filament heating in electronics (radio tubes): heating enables electron emission from a cathode

• Risks:

  • Overheating wires/devices can lead to fires (e.g., covering a blower fan so airflow stops; overloaded wiring; burning insulation/varnish).

2) Magnetic action

• Phenomenon: A current-carrying coil behaves like a magnet and can attract iron nails.

• Key idea demonstrated:

  • current flows through a coil → coil acquires magnetic properties → nails are attracted

• Iron core enhancement (electromagnet behavior):

  • inserting an iron core into the coil strongly increases the magnetic effect

• Related simultaneous effects:

  • Thermal and magnetic effects can occur at the same time
  • A compass needle would deflect near a current-carrying conductor (current affects magnet-like objects)

• Applications:

  • Magnetic separation: waste sorting; removing iron impurities from flour
  • Magnetic locks / intercoms in multi-storey buildings
  • Electromagnetic cranes in ports and industrial environments
  • Magnetic levitation trains
  • Electromagnetic braking for trams (rapid emergency stopping)

3) Chemical action

• Phenomenon: Passing current through a liquid electrolyte causes chemical changes at the electrodes.

• Demonstration described:

  • Electrolyte: aqueous copper(II) sulfate solution (blue solution)
  • Electrodes: carbon rods
  • At the cathode (negative electrode): copper deposits as a metallic layer
  • At the anode (positive electrode): more complex processes occur, but no obvious deposition is shown in the described setup

• Ion decomposition concept (for copper sulfate in water):

  • CuSO₄ dissociates into ions (conceptually):
    • Cu²⁺ (copper ions with +2 charge)
    • SO₄²⁻ (sulfate ions with −2 charge)

• Deposition causal chain (as described):

  • Cu²⁺ migrates to the cathode (negative)
  • Cu²⁺ gains electrons from the cathode → becomes metallic Cu, forming a copper layer

• Applications of chemical action:

  • Electrolysis / decomposition:
    • Decomposition of water into hydrogen and oxygen
    • Obtaining pure metals from compounds (alkali metals mentioned; sodium; industrial aluminum production)
  • Copper refining: purification to remove impurities that worsen conductivity
  • Electroplating / electrochemical coating: gilding, silver plating, cadmium plating, nickel/chrome on bike parts
  • Gold plating in microelectronics: gold is chemically inactive (doesn’t oxidize), enabling reliable contacts for microcircuit pins/sockets

4) Light effect (LEDs)

• New/mentioned concept: Current through a semiconductor diode (LED) produces light directly.
• Applications:
  • LED backlighting in screens (AMOLED mention; also LED components in crystal displays)

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Methodologies / step-by-step experimental outline (as shown)

Thermal effect setup

• Connect a copper wire between a current source terminals with a switch.
• Increase current gradually.
• Observe heating-driven wire sagging.
• Turn off current and observe the return behavior.

Magnetic effect setup

• Wrap a coil with copper wire on a frame.
• Place iron nails near/into the coil region.
• Connect the coil to a current source.
• Observe that nails are attracted when current flows.
• Repeat/extend with an iron core inside the coil to see the stronger effect.

Chemical effect setup

• Put carbon electrodes into a beaker with aqueous CuSO₄.
• Connect one electrode to positive (anode) and the other to negative (cathode).
• Close the circuit (current flows).
• Observe red copper deposition on the cathode.

Light effect concept

• Pass current through an LED.
• Observe emission of light.

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Researchers / sources featured (named)

• Пёрышкин (Peryshkin) — textbook referenced for lesson structure and homework
• Лукашик (Lukashik) — problems referenced for homework
• Paul III — mentioned in an anecdotal historical context about aluminum