Heating Effect Applications MCQs Quiz | Class 10

Heating Effect of Electric Current and its Applications

Overview:

When an electric current flows through a conductor, it encounters resistance. This resistance opposes the flow of electrons, causing them to collide with atoms in the conductor. These collisions transfer kinetic energy to the atoms, increasing their internal energy and, consequently, their temperature. This phenomenon is known as the heating effect of electric current, or Joule heating. It is described by Joule’s Law: Heat produced (H) = I²Rt, where I is the current, R is the resistance, and t is the time for which the current flows. This effect is utilized in various everyday electrical appliances.

Key Concepts:

• Joule’s Law: H = I²Rt. Heat generated is proportional to the square of current, resistance, and time.
• Resistance: The opposition to the flow of electric current. Materials with high resistance are good for heating elements.
• Power (P): The rate at which electrical energy is consumed or produced (P = V×I = I²R = V²/R).
• Electrical Energy (E): E = P×t = V×I×t.

Applications of Heating Effect of Electric Current:

1. Electric Iron:

• Principle: Works on the heating effect of electric current.
• Heating Element: Made of Nichrome (an alloy of nickel and chromium). Nichrome is preferred because it has high resistivity, high melting point, and does not oxidize easily even at high temperatures.
• Construction: The Nichrome wire is wound on a mica sheet (an excellent insulator and good conductor of heat) and placed between two iron plates. A thermostat controls the temperature by switching the current on and off.

2. Electric Heater:

• Principle: Similar to an electric iron, it uses the heating effect of current to generate heat.
• Heating Element: Also commonly made of Nichrome wire. The wire is coiled to increase its length in a compact space, thus increasing resistance and heat production.
• Operation: When current passes through the high-resistance Nichrome element, it heats up, radiating heat into the surroundings.

3. Filament Bulb (Incandescent Bulb):

• Principle: Electrical energy is converted into heat energy, which then makes the filament glow (incandescence) at very high temperatures (2700 K – 3300 K).
• Filament Material: Almost exclusively made of Tungsten. Tungsten has an extremely high melting point (around 3400 degrees C) and high resistivity, allowing it to glow brightly without melting.
• Inert Gas Filling: The glass bulb is evacuated and then filled with chemically inactive gases like Argon and Nitrogen. This prevents the tungsten filament from oxidizing and evaporating too quickly at high temperatures, significantly prolonging its lifespan.
• Efficiency: Incandescent bulbs are not very energy-efficient as a large portion (around 90-95%) of the electrical energy is converted into heat rather than light.

Other Important Applications:

• Electric Toaster: Uses Nichrome elements to toast bread.
• Electric Geyser/Water Heater: Uses high-resistance elements to heat water.
• Electric Fuse: A safety device that protects circuits from excessive current. It has a high resistance and a low melting point, so it melts and breaks the circuit when the current exceeds a safe limit.

Quick Revision:

• Joule’s Law: H = I²Rt.
• Heating elements (irons, heaters) use Nichrome: high resistance, high melting point, no easy oxidation.
• Filament bulbs use Tungsten: very high melting point, high resistivity.
• Inert gases (Ar, N₂) in bulbs prevent filament evaporation.
• Fuses use low melting point, high resistance wire for protection.

Practice Questions:

1. Name the law that explains the production of heat in a conductor when current passes through it.
2. Why is copper generally not used for making the heating element of an electric heater?
3. What is the purpose of a thermostat in an electric iron?
4. If an electric heater draws 5 A of current when connected to a 220 V supply, calculate the resistance of its heating element.
5. Why are incandescent bulbs considered less energy-efficient compared to LED bulbs?