Electric Current and its Effects

Electric Current and its Effects

Learning Objectives

• Understand simple electric circuits.
• Recognize symbols of electric components.
• Describe the heating effect of electric current.
• Explain the magnetic effect of electric current.
• Understand electromagnets and their working.
• Understand the principle and working of an electric bell.

Simple Electric Circuit

• Electric current is the flow of electric charge through a conductor.
• An electric circuit is an unbroken path through which electric current flows from a source to various components.
• A simple electric circuit consists of components like a bulb, a key (switch), and a dry cell.
• Complicated circuits may include ammeters, voltmeters, resistors, capacitors, etc.
• Symbols are used to represent circuit components for convenience.

Symbols of Electric Components

• Scientists use symbols to represent electrical circuits in a shorthand way.
  • Electric Cell: Represented by two parallel lines, one longer (positive terminal) and one shorter (negative terminal).
  • Electric Bulb: Represented as a coil.
  • Switch: Symbols represent 'ON' and 'OFF' positions.
  • Battery: Combination of two or more cells. Cells are placed in such a way that the positive terminal of one cell is connected to the negative terminal of the next cell.
  • Wire: Represented by a straight line.
  • Resistor: Fixed resistance wire represented by a zigzag line; it controls electric current flow.
  • Variable Resistance: Represented by a zigzag line with an arrow over it.
  • Ammeter: Measures the magnitude of current.
  • Voltmeter: Measures the potential difference across two points.
  • Galvanometer: Shows the direction of electric current flow in the circuit.

Circuit Types

• Series Circuit: Two or more components are connected one after the other.
• Parallel Circuit: Components are placed such that each comprises a simple circuit, placed parallel to each other.

Try and Learn - Cell Holder

• Aim: To prepare a cell holder and battery at home.
• Requirements: Wooden block, two iron strips or nails, two cells, and rubber bands.
• Procedure:
  • Fix two iron strips on a wooden block, separated by the length of two cells.
  • Connect a wire to each of the metal strips.
  • Fix the cells between the iron strips and tighten with a rubber band.

Cautions

• Do not touch a lighted bulb connected to the mains as it may be hot and burn your hand.
• Never use electric supply from A.C. mains, a generator, or an inverter for experiments; use dry cells.
• Never keep the switch 'ON' for a long time; otherwise, the cell may become weak quickly.

Miniature Circuit Breaker (MCB)

• MCBs are used in place of fuses and automatically switch off when the current exceeds a safe limit.
• Turning the switch on completes the circuit again.
• Look for the ISI mark when buying MCBs.

Reasons for Excessive Current:

1. Short Circuit: May arise due to defects in house wiring or worn insulation.
2. Overload: Connecting many devices to a single socket.

• Short circuits and overloads can cause fires.

Try and Learn - Electric Fuse

• Aim: To make an electric fuse.
• Requirements: Battery of four cells, a thin strand of steel wool, switch, and connecting wires.
• Procedure:
  • Connect the steel wool wire between two copper wires.
  • Connect the wires to a switch and battery.
  • Switch on the circuit; the steel wool wire becomes red hot and breaks, similar to how an electric fuse works.

Heating Effect of Electric Current

• When a bulb is switched on, it glows and becomes warm.
• The heating effect of current is used in appliances like immersion heaters, hot plates, irons, geysers, electric kettles, and hair dryers.
• These appliances contain an element (coil of wire), often made of nichrome.
• Nichrome offers high resistance to the flow of electric current and heats up to a high temperature.
• The filament of a bulb is made of thin, high-resistance tungsten, which heats up and emits light when current flows through it.

Compact Fluorescent Lamp (CFL)

• CFLs are designed to replace bulbs in existing light fixtures.
• CFLs use less power, have a longer life, and provide the same amount of visible light but may have a higher purchase price.
• Look for the ISI mark when buying CFLs.

Electric Fuse

• A fuse is a safety device used in an electric circuit to prevent damage from excessive current.
• It works on the principle of the heating effect of electric current.
• A fuse consists of a thin wire made of an alloy with a low melting point, placed inside a glass or ceramic container.
• If a high current passes through it, the fuse wire melts, breaking the circuit and stopping the flow of current to avoid damage.

Try and Learn - Open and Closed Circuits

• Aim: To show that a bulb glows only when the circuit is closed.
• Requirements: Two cells, cell holder, bulb, switch, and copper wires with coating.
• Procedure:
  • Place cells in the cell holder with positive connected to negative.
  • Connect the bulb and key with the holder.
  • The bulb glows when the switch is in the 'ON' position (closed circuit) and does not glow when the switch is in the 'OFF' position (open circuit).
• Conclusion: The bulb glows only when the switch is in the 'ON' position.

Open and Closed Circuits Defined:

• Open Circuit: The circuit in which electrical contact at any point is broken, preventing current flow.
• Closed Circuit: The circuit in which electric current flows from one terminal of the battery to the other.
• A broken filament in a bulb results in an open circuit, causing the bulb to fuse and not glow.

Heating Effect Experiment

• Aim: To show the heating effect of current.
• Requirements: Nichrome wire, switch, two cells, cell holder, and connecting wires.
• Procedure:
  • Take nichrome wire and make a coil from it.
  • Now make a circuit as shown below.
    *Now switch ON the circuit. After some time touch the coil.
• It can be concluded: from this activity that the coil gets hot when an electric current passes through it.

Joule's Law of Heating

• The production of heat in a conductor when electricity flows through it is called the heating effect of current.
• Joule's law states that heat produced is directly proportional to:
  • The strength of the electric current.
  • The material resistance of the conductor.
  • Time [t] for which current flows.
• As per requirement someone may use different materials of different thickness and different lengths.