Heating Effect of Electric Current MCQs Quiz | Class 10

Understanding the Heating Effect of Electric Current

The heating effect of electric current, also known as Joule heating, is a fundamental concept in physics that explains how electrical energy is converted into heat energy when an electric current passes through a conductor. This phenomenon is crucial for the operation of many common household appliances and is also essential for safety mechanisms like fuses.

Joule’s Law of Heating

When an electric current (I) flows through a resistor with resistance (R) for a time (t), the heat (H) produced is given by Joule’s Law:

H = I²RT

Where:

• H is the heat produced in Joules (J).
• I is the current flowing through the conductor in Amperes (A).
• R is the resistance of the conductor in Ohms (Ω).
• T is the time for which the current flows in seconds (s).

This law states that the heat produced is directly proportional to the square of the current, the resistance of the conductor, and the time for which the current flows.

Applications of Heating Effect of Electric Current

Many everyday appliances are designed to utilize the heating effect of electric current:

1. Electric Heaters, Irons, and Toasters: These appliances contain a heating element, usually made of an alloy like nichrome. Alloys have a high resistance and a high melting point, which allows them to produce a significant amount of heat without melting when current passes through them.
2. Electric Bulbs (Incandescent Lamps): The filament of an incandescent bulb is made of tungsten, which has an extremely high melting point. When current passes through the filament, it heats up to a very high temperature (around 2700 degrees Celsius) and glows, emitting light.
3. Electric Kettles and Water Heaters: Similar to irons, these devices use a high-resistance heating element submerged in water to transfer heat efficiently and raise the water’s temperature.

Electric Fuse: A Safety Device

While the heating effect is useful, excessive current can lead to overheating, causing damage to appliances or even fires. This is where an electric fuse comes in as a crucial safety device.

• Purpose: A fuse protects electrical circuits and appliances from high currents (due to short-circuiting or overloading).
• Principle: A fuse consists of a short piece of wire made of a material with a low melting point and relatively high resistance, such as an alloy of lead and tin.
• Working: It is connected in series with the live wire of the circuit. If the current in the circuit exceeds a safe limit, the fuse wire heats up rapidly due to Joule heating, melts, and breaks the circuit. This disconnects the faulty appliance or overloaded circuit from the power supply, preventing damage.
• Modern Alternatives: Miniature Circuit Breakers (MCBs) are increasingly used instead of fuses. MCBs are automatic switches that turn off when current exceeds the safe limit and can be reset manually.

Quick Revision Checklist

• Joule’s Law: H = I²RT.
• Heat produced depends on current squared, resistance, and time.
• Heating elements are made of high-resistance, high-melting point alloys (e.g., nichrome).
• Tungsten is used in bulb filaments due to its high melting point.
• Fuses protect circuits from overloading and short circuits.
• Fuse wire has a low melting point and is connected in series with the live wire.

Extra Practice Questions

1. Explain why the connecting wires in an electric circuit usually do not glow, while the filament of an electric bulb does.
2. An electric heater of 1000 W power is used for 2 hours daily. Calculate the energy consumed in Joules. (Hint: Power = Energy / Time)
3. What is the function of the earth wire in a household electrical circuit? (While not directly about heating effect, it relates to electrical safety).
4. Name two properties of a material that make it suitable for a fuse wire.
5. If the resistance of a heating element is halved while keeping the current constant, how would the heat produced change in a given time?