You are here
Heating Effect of Electric Current
- Pass current through a wire and the wire gets warm.
- The current faces opposition called resistance.
- Different wires offer different resistance.
- Nichrome wire offers more resistance than copper.
- This resistance turns some electrical energy into heat.
Example 1 — Nichrome Wire
- Current passes through a nichrome wire.
- The wire feels warm to touch.
- So the current makes a heating effect.
Example 2 — Electromagnet Wire
- The wire of an electromagnet is used for a while.
- Its ends become warm.
- So even this wire shows the heating effect.
Important Points
- More current makes more heat.
- Heat depends on the wire's material, thickness, length, and time.
Definition — Heating Effect of Electric Current
When electric current passes through a conductor, it gets heated. This warming is the heating effect of electric current.
Definition — Resistance
Resistance is the opposition a conductor offers to the flow of electric current through it.
Materials needed
A cardboard piece and two nails.
A nichrome wire, about 0.3 mm thick and 10 cm long.
An electric cell, a cell holder, a switch, and connecting wires.
A nichrome wire, about 0.3 mm thick and 10 cm long.
An electric cell, a cell holder, a switch, and connecting wires.
Procedure
Mount the nails about 5 cm apart on the cardboard.
Tie the nichrome wire between them and join the circuit.
Touch the wire with the switch OFF.
Move the switch ON for about 30 seconds, then OFF.
Touch the wire for a moment (do not hold it).
Tie the nichrome wire between them and join the circuit.
Touch the wire with the switch OFF.
Move the switch ON for about 30 seconds, then OFF.
Touch the wire for a moment (do not hold it).
Observation
The wire feels warm after the current flows. Before the current, it felt cool.
Explanation
The wire resists the current, so some electrical energy becomes heat. So the current heats the wire.
◆ Summary
- Wire cool when OFF.
- Wire warm after current.
- Resistance makes heat.
- This is the heating effect.
⚠️ Safety First
Do not touch the wire for a long time, to avoid any injuries.
🔭 Think Like a Scientist — Heat With Two Cells
Do this only with a teacher. Repeat Activity 4.5 with a battery of 2 cells. Does the wire heat up more with one cell or two?
What you find
The wire heats up more with 2 cells. This is because the heat depends on the amount of current. The heat in a wire also depends on its material, thickness, length, and the time the current flows.
Heating Appliances in Daily Life
- An incandescent lamp glows because its filament is heated.
- Many home appliances use the same heating effect.
- Examples are heaters, stoves, irons, kettles, and hair dryers.
- Each has a rod or coil of wire called a heating element.
Example 1 — Electric Room Heater
- Current passes through the heater's element.
- The element gets red hot and warms the room.
- So it works on the heating effect.
Example 2 — Immersion Rod
- An immersion rod is put in water with current on.
- Its coil heats up and warms the water.
- So it also uses the heating effect.
Important Points
- In some appliances the heating element can be seen glowing red hot.
- Overheating can melt plastic parts or even cause fires.
Definition — Heating Element
A heating element is the rod or coil of wire in an appliance that gets hot when current flows through it.
⭐ A Step Further — Safe Switchboards
To stop unwanted heating in switchboards, use wires, plugs, and sockets rated for the right current.
🏭 Ever Heard Of — Electric Furnaces
The heating effect is also used in industry.
In steel plants, a high-temperature electric furnace uses current to make heat. This melts and recycles scrap steel into usable steel.
🧠 Test Yourself — Section 4.2
-
Why does a current carrying wire get warm?
View Answer
The wire resists the current, so some electrical energy turns into heat. -
What is resistance?
View Answer
The opposition a conductor offers to the flow of current. -
Which heats more for the same size, nichrome or copper?
View Answer
Nichrome, because it has higher resistance than copper. -
What does the heat in a wire depend on?
View Answer
The current, and the wire's material, thickness, length, and time of flow. -
What is a heating element?
View Answer
The rod or coil of wire in an appliance that gets hot when current flows.
📋 NCERT Question 3 — Warm wire and deflected compass
Current flows through a nichrome wire: the wire becomes warm, and a compass below it deflects. Which statements are correct? (MCQ)
View Answer →
📋 NCERT Question 4 — Match the columns
Match Voltaic cell, electric iron, nichrome wire, and electromagnet with chemical reactions, heating effect, and magnetic effect.
View Answer →
📋 NCERT Question 5 — Why nichrome is used
Why is nichrome wire commonly used in electrical heating devices? (MCQ)
View Answer →
📋 NCERT Question 6 — Electric heating vs firewood
Give reasons why electric heating devices are often more convenient than burning firewood or charcoal, considering societal impact.
View Answer →
