Electric Current and Its Effects
Understand current, circuits, heating and magnetic effects of electric current with real-life examples, simple explanations, and exam-ready notes.
Introduction
Electricity powers our homes, schools, hospitals, phones, fans, bulbs, computers, and almost every modern device we touch. But what actually flows in the wires, why do bulbs glow, how do magnets appear from a simple nail and a wire, and why does a fuse “blow” when there is a short circuit? In this chapter, we learn that electric current is the flow of electric charges through a conductor, usually a metal wire, and that this flow produces two very important effects: a heating effect (things warm up when current passes) and a magnetic effect (a current-carrying conductor behaves like a magnet). We will explore simple circuits using cells, switches, and bulbs, read standard circuit symbols, understand series vs. parallel connections with real-life comparisons, discover why an electric iron gets hot, how a filament bulb glows, why an LED saves energy, how a coil of wire around an iron nail becomes an electromagnet that can pick up pins, and how safety devices like fuses and MCBs protect us from electric hazards. By the end, you will be able to draw neat circuits, predict what happens when a switch is opened or a bulb is fused, explain everyday appliances like heaters and doorbells, and write exam-ready answers with clear examples and keywords.
What is Electric Current?
Electric current is the rate at which electric charge flows through a conductor. In simple terms, it tells us how much charge passes a point in the wire every second.
The basic relation is I = Q / t where I is current (ampere, A), Q is charge (coulomb, C), and t is time (seconds).
Sources of current (Cells & Batteries)
- Cell: A single source of electric energy (e.g., 1.5 V dry cell).
- Battery: Two or more cells connected together. In series, voltages add up.
Conductors and Insulators
Conductors: Allow current to pass easily (copper, aluminum, iron, water with salts).
Insulators: Do not allow current to pass easily (plastic, rubber, glass, dry wood).
| Material | Type | Where used |
|---|---|---|
| Copper wire | Conductor | Inside cables & circuits |
| Rubber/PVC | Insulator | Wire covering (sheath) |
| Glass/Porcelain | Insulator | Bulb body, insulators on poles |
Electric Circuit & Symbols
An electric circuit is a closed path that allows current to flow from the positive terminal of a cell, through wires and devices, back to the negative terminal.
Common circuit symbols
| Component | Symbol description (text) | Use |
|---|---|---|
| Cell | Short + long line | Source of electric energy |
| Battery | Several cell symbols in series | Higher voltage source |
| Switch (open/closed) | Break/connected line | Control the circuit |
| Bulb/Lamp | Circle with cross/filament | Glows when current flows |
| Resistor | Zig-zag line/rectangle | Opposes current, produces heat |
| Wire | Straight line | Conducting path |
| Electromagnet | Coil around core | Acts like a magnet when current flows |
Series vs Parallel (with examples)
- Series: One after another; if one bulb fuses, the circuit breaks and all bulbs go off (like old fairy lights).
- Parallel: Multiple branches; if one bulb fuses, others keep glowing (like home wiring for lights and fans).
Heating Effect of Current
When electric current flows through a conductor, it faces opposition called resistance. Because of this resistance, part of the electrical energy changes into heat energy. This is known as the heating effect of electric current. Everyday examples include the glow of a bulb’s filament, a geyser or immersion rod heating water, the hot plate of an electric iron smoothing clothes, and a toaster browning bread. The amount of heat produced depends on (i) the current passing through the conductor, (ii) the resistance of the conductor, and (iii) the time for which the current flows. Greater current, higher resistance, or longer time means more heat. That is why a thin, high-resistance filament in a bulb gets very hot and glows, while the thick copper wires in the circuit remain comparatively cool. Devices that use the heating effect (like heaters) are designed to handle heat safely, while safety devices like fuses melt deliberately if too much current flows, protecting our appliances from damage.
Daily uses of heating effect
- Filament bulb: A tungsten filament glows white-hot when current passes.
- Electric iron/heater: Nichrome coil heats up and transfers heat to clothes/air/water.
- Fuse wire: Melts to break the circuit when current exceeds a safe value.
Magnetic Effect of Current
A fascinating property of electric current is that it creates a magnetic field around the conductor. This is called the magnetic effect of electric current. If you place a small compass near a wire carrying current, the compass needle deflects, proving that a magnetic field is present. Wrapping the wire into a coil (a solenoid) concentrates and strengthens this magnetic field. Placing a piece of soft iron inside the coil makes the field even stronger. This principle is used to make electromagnets, which can be switched on and off by controlling the current. Electromagnets are used in doorbells, electric bells, relays, cranes in junkyards to lift iron scrap, speakers, and many toys. The direction of the magnetic field around a straight wire can be found by the right-hand thumb rule: if you hold the wire with your right hand and point your thumb in the direction of current, your curled fingers show the direction of the magnetic field lines.
Making an Electromagnet (Simple Activity)
- Take an iron nail, insulated copper wire, two 1.5 V cells, and a switch.
- Wind the wire tightly around the nail to make many turns (leave wire ends free).
- Connect the coil to the cells and switch. Close the switch.
- Try to pick up paper clips/pins. The nail behaves like a magnet while current flows.
- Open the switch—the nail loses magnetism. That’s why it’s called an electromagnet.
Fuses, MCBs & Electrical Safety
A fuse is a thin wire that melts and breaks the circuit when excessive current flows. It prevents fire and protects appliances. Modern homes often use MCBs (Miniature Circuit Breakers) which trip OFF automatically and can be reset.
- Use proper rating fuses/MCBs for circuits.
- Never overload a socket with many high-power devices.
- Keep hands dry; do not touch open wires.
- Always switch OFF before changing bulbs or checking appliances.
Real-life Examples & Applications
Heating Effect examples
- Bulb filament: Thin tungsten glows due to heat.
- Room heater/geyser: Nichrome coil converts electrical energy to heat.
- Electric kettle: Heating element warms water quickly.
- Fuse: Melts to prevent damage during overcurrent.
Magnetic Effect examples
- Doorbell/electric bell: Electromagnet pulls a striker to hit the bell.
- Relays: Small current controls a bigger circuit safely.
- Speakers: Current in coil interacts with magnet to move the cone and produce sound.
- Cranes: Giant electromagnets lift iron scrap in junkyards.
Worked Example (Reasoning)
Q: Why does a thin filament in a bulb heat more than a thick connecting wire?
A: The thin filament has higher resistance (R), so for the same current, more heat is produced (H ∝ I²Rt), making it glow, while thick copper wires have very low resistance and stay relatively cool.
FAQs & Practice Questions
Short Answer
- Define electric current. State its SI unit.
- What is the heating effect of current? Give two uses.
- How can you make an electromagnet stronger?
- Why does a fuse wire melt during excessive current?
True/False
- Current flows in an open circuit. — False
- Electromagnets can be switched ON and OFF. — True
- Parallel circuits keep other bulbs ON if one bulb fuses. — True
Match the Following
| Column A | Column B |
|---|---|
| Fuse | Safety device that melts |
| Electromagnet | Coil + iron core |
| Bulb filament | Glows due to heating |
| Parallel circuit | Independent branches |
Quick Summary (Exam-Ready)
- Electric current = flow of charges; needs a closed circuit.
- Heating effect: Current through resistance produces heat; used in bulbs, irons, kettles; basis of fuse.
- Magnetic effect: Current creates magnetic field; used in electromagnets, bells, relays, cranes.
- Series vs Parallel: Series—one breaks, all off; Parallel—others stay ON.
- Safety: Correct fuse/MCB rating, avoid overloading, dry hands, switch OFF before handling.
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