Chapter 14: Electric Current and Its Effects
विद्युत धारा और इसके प्रभाव (तापीय प्रभाव, विद्युत फ्यूज एवं विद्युत चुंबक)
Don't Let a 20-Minute Bubbling Delay Cost You CTET Qualification
In offline CTET exams, bubbling 150 bubbles takes 18 to 22 minutes of mechanical time. A single misaligned row can trigger an 8-question domino error. Practice bubble-filling this chapter's solved MCQs inside Mentora's official OMR simulator.
- Circuit diagram symbols: Long thin vertical line represents positive terminal; shorter thicker line represents negative terminal; open/closed switch representation.
- Heating Effect of Electric Current: When electric current flows through a high-resistance wire, the wire gets extremely hot (Joule heating).
- Heating Elements: In appliances like electric heaters, geysers, toasters, and irons, the heating coil is made of **Nichrome** wire (an alloy of nickel and chromium with high resistivity and high melting point) that glows red-hot without oxidizing.
- Electric Fuse: Essential safety device containing a specialized wire with a **low melting point**. When excess electric current surges through the circuit, the wire gets overheated, melts, and breaks the circuit, preventing electrical fires and equipment damage. Modern replacement: **MCB (Miniature Circuit Breaker)** which automatically flips off.
- Magnetic Effect of Electric Current (Hans Christian Oersted 1820): Passing electric current through a conducting wire generates a magnetic field around it, causing a nearby magnetic compass needle to deflect.
- Electromagnet (विद्युत चुंबक): An insulated wire coiled tightly around a soft iron core (like an iron nail) functions as a magnet when electric current flows through the coil. It loses magnetism immediately when current is switched off. Uses: Scrapyard cranes lifting steel, telephone earpieces, relays, and electric bells.
- Electric Bell mechanism: Consists of an electromagnet, a soft iron armature with a striker hammer, a gong, and a contact screw. Current energizes electromagnet -> attracts armature -> hammer strikes gong -> contact breaks at screw -> current stops -> spring restores armature -> cycle repeats rapidly.
- Trap: What property must an electric fuse wire possess? Correct: LOW MELTING POINT (so it melts before building wiring overheats).
- Trap: Who discovered the magnetic effect of current? Correct: HANS CHRISTIAN OERSTED (not Faraday, not Newton).
- Trap: Does an electromagnet retain magnetism after current is switched off? Correct: No, it behaves as a TEMPORARY magnet and loses magnetism immediately.
NCERT Core Facts: Electrical Heating, Fuses & Electromagnetism
In CTET Paper 2 Science, questions on electric fuse wire melting points, heating element alloys, and Oersted's deflection experiment appear regularly.
1. Electrical Circuit Diagram Symbols
- Electric Cell: Long thin line represents the Positive Terminal ($+$); short thick line represents the Negative Terminal ($-$).
- Battery: Combination of two or more cells joined in series (positive terminal of one cell connected to negative terminal of the next).
- Switch: Can be placed anywhere in the circuit. When "ON", the circuit is complete (closed); when "OFF", the circuit is broken (open).
2. Heating Effect of Electric Current
- When current flows through a conducting wire with electrical resistance, electrical energy converts into thermal energy:
- Heating Elements (हीटिंग एलीमेंट):
- Appliances: Electric geysers, immersion rods, room heaters, electric irons.
- Coil Material: Made of Nichrome wire (Nickel-Chromium alloy).
- High electrical resistance + high melting point enables it to glow red-hot without burning or melting.
The Electric Fuse (Safety Benchmark)
3. Magnetic Effect & The Electromagnet
- Discovery (1820): Danish physicist Hans Christian Oersted noticed that whenever electric current flowed through a nearby wire, a magnetic compass needle deflected from its north-south alignment.
- Electromagnet Structure:
- Insulated copper wire wrapped around a soft iron nail.
- When current flows, the iron core becomes magnetized.
- Unlike permanent lodestone magnets, an electromagnet is temporary: it loses its magnetic attraction the instant current is switched off.
- Real-World Applications:
- Industrial cranes lifting scrap iron and heavy steel plates.
- Medical removal of magnetic iron splinters from eyes.
- Acoustic telephone diaphragms and loudspeakers.
- The Electric Bell (विद्युत घंटी).
Test Your Mastery: Electric Current and Its Effects
Authentic CBSE exam questions tested directly from this NCERT chapter.
An electric fuse is a safety device used in electrical circuits. Which property must the wire used in an electric fuse have?
विद्युत फ्यूज एक सुरक्षा युक्ति है जिसका उपयोग विद्युत परिपथों में किया जाता है। विद्युत फ्यूज में प्रयुक्त तार में कौन-सा गुण होना चाहिए?
When a magnetic compass needle is placed near a straight wire carrying electric current, the needle deflects. This phenomenon was first discovered by:
जब किसी धारावाही चालक तार के पास चुंबकीय सुई रखी जाती है, तो वह विक्षेपित हो जाती है। इस परिघटना की खोज सर्वप्रथम किसने की थी?
Which of the following electrical appliances does NOT work on the heating effect of electric current?
निम्नलिखित में से कौन-सा विद्युत उपकरण विद्युत धारा के तापीय प्रभाव पर कार्य नहीं करता है?
Why does an electric fuse wire have a low melting point?
So it easily melts and breaks the circuit when dangerous excess current surges, preventing electrical fires.
What is the heating element in an electric iron made of?
Nichrome wire, an alloy of nickel and chromium with high resistance and high melting point.
Who discovered the magnetic effect of electric current?
Hans Christian Oersted in 1820 discovered that electric current deflects a compass needle.