ANAND CLASSES Study Material and Notes to learn the Heating Effect of Electric Current with detailed explanation, Joule’s law formula, solved numericals, and practical applications like electric heaters and bulbs. Perfect for CBSE Class 10 Science students. It includes FAQs, conceptual Q&A, MCQs with explanations, a “Do You Know?” section, a worksheet, a test paper with marks distribution, and key points for quick revision.

🔥 Heating Effect of Electric Current

When an electric current flows through a high-resistance wire like nichrome, the wire becomes very hot and produces heat. This is known as the heating effect of current.

This heating effect occurs due to the conversion of electrical energy into heat energy, much like how mechanical energy overcomes friction and converts into heat.

Just as friction resists motion, electrical resistance resists current and generates heat. Let’s understand this concept in detail and derive the formula for heat produced.

🔧 Derivation of Heat Produced (Joule’s Law)

Let:

• I = Current (in amperes)
• R = Resistance (in ohms)
• t = Time (in seconds)
• V = Potential difference (in volts)
• Q = Charge (in coulombs)

Work done by current

Since a conductor, say a resistance wire, offers resistance to the flow of current, so work must be done by the current continuously to keep itself flowing. We will calculate the work done by a current I when it flows through a resistance R for time t. Now, when an electric charge Q moves against a potential difference V, the amount of work done is given by :

$$W = Q \times V \tag{1}$$

From the definition of current: $$I = \frac{Q}{t} \Rightarrow Q = I \times t \tag{2}$$

From Ohm’s Law: $$V = I \times R \tag{3}$$

Substituting (2) and (3) into (1): $$W = (I \times t) \times (I \times R) = I^2 R t$$

So, Work done by current flow against resistance R for time time t is given by :

$$W = I^2 R t$$

Assuming that all the electrical work done or all the electrical energy consumed is converted into heat energy, we can write ‘Heat produced’ in place of ‘Work done’ in the above equation. Thus,

Heat Produced H is given by :

$$ H = I^2 R t$$

This formula gives us the heat produced in joules when a current of I amperes flows in a wire of resistance R ohms for time t seconds. This is known as Joule’s law of heating.

So, the heat produced (H) is: $$\boxed{H = I^2 R t \text{ joules}}$$

⚖️ Joule’s Law of Heating

According to Joule’s Law:

The heat produced in a conductor is directly proportional to:

• The square of current (I²)
• The resistance of the wire (R)
• The time for which current flows (t)

🔁 Variation with Factors:

• Current Law : $H \propto I^2$
  • If current is doubled, heat becomes 4 times.
  • If current is halved, heat becomes 1/4.
• Resistance Law : $H \propto R$
  • More resistance → More heat produced.
  • For same current, nichrome (high resistance) produces more heat than copper.
• Time Law : $H \propto t$
  • Double the time → Double the heat.
  • Half the time → Half the heat.

🧮 Sample Problems

✅ Problem 1: A potential difference of 250 volts is applied across a resistance of 500 ohms in an electric iron. Calculate (i) current, and (ii) heat energy produced in joules in 10 seconds.

Solution :

Given:
$V = 250 \, \text{V}, \, R = 500 \, \Omega, \, t = 10 \, \text{s}$

(i) Current: $I = \frac{V}{R} = \frac{250}{500} = 0.5 \, \text{A}$

(ii) Heat Produced: $H = I^2 R t = (0.5)^2 \times 500 \times 10 = 1250 \, \text{J}$

✅ Problem 2: Calculate the heat produced when 96,000 coulombs of charge is transferred in 1 hour through a potential difference of 50 volts.

Solution :

Given:
$Q = 96,000 \, \text{C}, \, V = 50 \, \text{V}, \, t = 1 \, \text{hour} = 3600 \, \text{s}$

Current : $I = \dfrac{Q}{t} = \dfrac{96,000}{3600} = 26.67 \, \text{A}$

Resistance : $R = \dfrac{V}{I} = \dfrac{50}{26.67} = 1.87 \, \Omega$

Heat Produced : $H = I^2 R t = (26.67)^2 \times 1.87 \times 3600 = 4788.4 \, \text{kJ}$

✅ Problem 3: Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then in parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be :
(a) 1 : 2 (b) 2 : 1 (c) 1 : 4 (d) 4 : 1

Solution :

Let resistance of each wire be x.

Series combination : When the two resistance wires, each having a resistance x, are connected in series, then

Combined resistance,

$$R_s = 2x$$

And, if the potential difference in the circuit is V, then current flow

$$I_s = \frac{V}{2x}$$

Suppose heat produced with the series combination of wires is H_s. Then :

$$H_s = I^2 R t = \left( \frac{V}{2x} \right)^2 \cdot 2x \cdot t = \frac{V^2 t}{2x}$$

Parallel Combination : When the two resistance wires, each of resistance x, are connected in parallel, then
Combined resistance,

$$R_p = \frac{x}{2}$$

And, if the potential difference in the circuit is V, then current flow

$$I_p = \frac{V}{R_p} = \frac{2V}{x}$$

Suppose the heat produced with the parallel combination of wires is H_p. Then :

$$H_p = I^2 R t = \left( \frac{2V}{x} \right)^2 \cdot \frac{x}{2} \cdot t = \frac{4V^2 t}{x}$$

Ratio of heat produced :

$$\dfrac{H_s}{H_p} = \dfrac{\dfrac{V^2 t}{2x}}{\dfrac{4V^2 t}{x}} = \dfrac{1}{4}$$

✅ Answer: (c) 1 : 4

💡 Applications of Heating Effect of Current

🔌 1. Electrical Heating Appliances

Used in:

• Electric iron
• Electric kettle
• Toaster
• Heater
• Geyser
• Hair dryer

All these heating appliances contain coils of high resistance wire made of nichrome alloy. When these appliances are connected to power supply by insulated copper wires then a large amount of heat is produced in the
heating coils (because they have high resistance), but a negligible heat is produced in the connecting wires of copper (because copper has very, very low resistance).

For example, the heating element (or coil) of an electric heater made of nichrome glows because it becomes red-hot due to the large amount of heat produced on passing current (because of its high resistance), but the cord or connecting cable of the electric heater made of copper does not glow because negligible heat is produced in it by passing current (because of its extremely low resistance). The temperature of the heating element (or heating coil) of an electrical heating device when it becomes red-hot and glows is about 900°C.

Electrical Heating Appliances :

➡️ Heating coils made with nichrome wire (high resistance).
➡️ Connecting copper wires (low resistance) carry current without heating.

💡 2. Electric Bulbs

The heating effect of electric current is utilised in electric bulbs (electric lamps) for producing light.

When electric current passes through a very thin, high resistance tungsten filament of an electric bulb, the filament becomes white-hot and emits light. Please note that the same current flowing through the tungsten filament of an electric bulb produces enormous heat but almost negligible heat is produced in the connecting wires of copper. This is because of the fact that the fine tungsten filament has very high resistance whereas copper connecting wires have very low resistance.

Tungsten metal is used for making the filaments of electric bulbs because it has a very high melting point (of 3380°C). Due to its very high melting point, the tungsten filament can be kept white-hot without melting away. The other properties of tungsten which make it suitable for making filaments of electric bulbs are its high flexibility and low rate of evaporation at high temperature. Please note that when the tungsten filament of an electric bulb becomes white-hot and glows to emit light, then its temperature is about 2500°C !

If air is present in an electric bulb, then the extremely hot tungsten filament would burn up quickly in the oxygen of air. So, the electric bulb is filled with a chemically unreactive gas like argon or nitrogen (or a mixture of both). The gases like argon and nitrogen do not react with the hot tungsten filament and hence prolong the life of the filament of the electric bulb. It should be noted that most of the electric power consumed by the filament of an electric bulb appears as heat (due to which the bulb becomes hot), only a small amount of electric power is converted into light. So, filament-type electric bulbs are not power efficient.

On the other hand, tube-lights are much more power efficient, because they have no filaments.

Hence Electric Bulbs :

• Use tungsten filament (high resistance, high melting point ~3380°C).
• Filament becomes white-hot (~2500°C) and emits light.
• Filled with argon or nitrogen gas to prevent oxidation.

❗ Not power-efficient: Most energy is converted into heat.

💥 3. Electric Fuses

The heating effect of electric current is utilised in electric fuse for protecting household wiring and electrical appliances.

A fuse is a short length of a thin tinplated copper wire having low melting point. The thin fuse wire has a higher resistance than the rest of the electric wiring in a house. So, when the current in a household electric circuit rises too much due to some reason, then the fuse wire gets heated too much, melts and breaks the circuit (due to which the current stops flowing). This prevents the fire in house (due to over-heating of wiring) and also prevents damage to various electrical appliances in the house due to excessive current flowing through them.

Thus, an electric fuse is a very important application of the heating effect of current.

Electric Fuses :

• Thin tin/copper wire with low melting point.
• Melts if current exceeds safe limit.
• Breaks the circuit and protects from fire or appliance damage.

Conceptual Questions and Answers

Q1: Do all electrical appliances convert electric energy into heat energy?

A: No, not all electrical appliances convert all the electric energy into heat energy. Only electrical heating appliances convert most of the electric energy into heat.

Q2: What happens to electric energy in appliances like fans?

A: In appliances like fans, most of the electric energy is used in mechanical work (turning the fan), and only a small amount is converted into heat. That is why fans become only slightly warm after running for a long time.

Q3: Which appliances convert most of the electrical energy into heat energy?

A: Electrical heating appliances such as electric heaters, electric kettles, hair dryers, immersion rods, and geysers convert most of the electrical energy into heat energy.

Q4: What is common in all electrical heating appliances?

A: All electrical heating appliances have a ‘heating element’ or ‘heating coil’ made of high resistance wire, such as nichrome.

Q5: Why is high resistance wire like nichrome used in heating appliances?

A: Nichrome and other high resistance wires are used because they help convert most of the electric energy into heat energy efficiently.

Q6: What is the key difference between a heating appliance and a non-heating appliance in terms of energy conversion?

A: A heating appliance converts most of the electric energy into heat, while a non-heating appliance like a fan or motor uses most of the electric energy for mechanical work, with minimal heat production.

Q7: How does the resistance of the wire affect heat production in electrical appliances?

A: Higher resistance wires, like nichrome, oppose the flow of electric current more, resulting in more heat production due to the heating effect of current (Joule’s law of heating).

Q8: Why is it important to use high resistance material in heating coils?

A: High resistance materials produce more heat for the same amount of electric current, making them efficient for heating applications.

Q9: What would happen if we use a low resistance wire instead of nichrome in a heater?

A: A low resistance wire would not produce enough heat, making the appliance inefficient and possibly unsafe, as it may cause overheating or short circuits.

Q10: How does the heating effect of electric current demonstrate energy conversion?

A: It shows that electrical energy can be converted into heat energy, especially when current flows through materials with high resistance.

✅ Frequently Asked Questions (FAQs)

Q1: Why doesn’t a fan produce much heat when in use?

A: A fan uses most of the electric energy for mechanical movement (turning the blades), and only a small amount is lost as heat, making it slightly warm during prolonged use.

Q2: Which appliances are specifically designed to produce heat?

A: Appliances like electric heaters, kettles, hair dryers, immersion rods, and geysers are designed to convert most of the electrical energy into heat energy.

Q3: What is the role of a heating element in electrical appliances?

A: The heating element, made of high resistance wire like nichrome, is responsible for converting electrical energy into heat energy.

Q4: What is nichrome and why is it used in heating appliances?

A: Nichrome is an alloy of nickel and chromium with high electrical resistance. It heats up quickly when current passes through it, making it ideal for heating appliances. Also alloys are not oxidised easily at this high temperature.

Q5: Can a non-heating electrical appliance become hot?

A: Yes, non-heating appliances like fans can become slightly warm due to the small amount of electric energy converted to heat, especially after running for a long time.

🔘 Multiple Choice Questions (MCQs) with Explanations

Q1. Which of the following appliances converts most of the electric energy into heat energy?
A. Electric fan
B. Electric bell
C. Electric heater
D. Electric motor

✅ Answer: C. Electric heater
Explanation: An electric heater is designed to convert the majority of electrical energy into heat using a high resistance heating element, typically made of nichrome.

Q2. What happens when an electric current flows through a fan?
A. All energy is converted into heat
B. Most energy is used to produce sound
C. Most energy is used for mechanical motion
D. Energy is stored in the fan

✅ Answer: C. Most energy is used for mechanical motion
Explanation: In a fan, electric energy is primarily used to rotate the blades (mechanical motion), and only a small amount is lost as heat, causing it to warm up slightly.

Q3. Which of the following materials is commonly used in heating elements of electrical appliances?
A. Copper
B. Aluminium
C. Nichrome
D. Silver

✅ Answer: C. Nichrome
Explanation: Nichrome is used because it has a high electrical resistance and does not oxidize easily at high temperatures, making it suitable for converting electrical energy into heat.

Q4. Why does a hair dryer produce hot air when switched on?
A. It contains a fan that generates heat
B. It uses sunlight
C. It has a heating element that converts electric energy into heat
D. It compresses air to generate heat

✅ Answer: C. It has a heating element that converts electric energy into heat
Explanation: Hair dryers contain a high resistance heating coil which gets hot when current passes through, heating the air blown by the internal fan.

Q5. An immersion rod becomes hot when connected to electricity because:
A. Water resists the current
B. It uses a heating coil with high resistance
C. It uses magnetic energy
D. It has a motor that rotates and produces heat

✅ Answer: B. It uses a heating coil with high resistance
Explanation: The immersion rod has a heating element (nichrome wire) with high resistance, which heats up when electric current flows through it, transferring heat to the water.

Q6. What is the main function of the heating element in electrical appliances like geysers or kettles?
A. To store electric energy
B. To reduce electric current
C. To convert electrical energy into heat energy
D. To produce light

✅ Answer: C. To convert electrical energy into heat energy
Explanation: The heating element is made of high-resistance material (like nichrome) which gets hot when current flows through it, thereby converting electrical energy into heat.

Q7. When an electric fan runs for a long time, it becomes slightly warm. What is the reason?
A. Due to mechanical motion
B. Due to magnetic effect
C. Due to small amount of electrical energy being converted into heat
D. Because it runs on solar energy

✅ Answer: C. Due to small amount of electrical energy being converted into heat
Explanation: In devices like fans, most energy is used for mechanical work, but a small part is converted to heat due to internal resistance, which causes warming.

Q8. Which of the following devices primarily utilizes the heating effect of electric current?
A. Transformer
B. Refrigerator
C. Electric iron
D. Generator

✅ Answer: C. Electric iron
Explanation: Electric irons are specifically designed to convert electrical energy into heat to press clothes, utilizing the heating effect of current.

Q9. Which property of nichrome makes it suitable for use in heating coils?
A. Low melting point
B. High electrical conductivity
C. High resistance and ability to withstand high temperature
D. High magnetic strength

✅ Answer: C. High resistance and ability to withstand high temperature
Explanation: Nichrome has high resistance, doesn’t oxidize quickly, and can withstand high temperatures, making it perfect for heating applications.

Q10. In a heating appliance, if the resistance of the heating coil is increased, what happens to the heat produced (assuming constant voltage)?
A. Heat decreases
B. Heat remains constant
C. Heat increases
D. Heat becomes zero

✅ Answer: A. Heat decreases
Explanation: According to the formula $H = \dfrac{V^2t}{R}$​, if resistance increases and voltage remains constant, heat produced decreases.

🔍 Assertion-Reason Based Questions

Instructions:
Read the following statements carefully and choose the correct option:
A. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
B. Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
C. Assertion is true, but Reason is false.
D. Assertion is false, but Reason is true.

Q1.
Assertion (A): An electric heater converts most of the electrical energy into heat energy.
Reason (R): Electric heaters have a high resistance heating element like nichrome.

✅ Answer: A
Explanation: Both statements are true and the reason correctly explains the assertion. The heating element’s high resistance causes it to get hot and convert electrical energy to heat efficiently.

Q2.
Assertion (A): An electric fan becomes hot when used for a long time.
Reason (R): The fan converts all the electrical energy into heat energy.

✅ Answer: C
Explanation: The assertion is true, but the reason is false. Only a small portion of the electrical energy is converted into heat; most is used for mechanical work.

Q3.
Assertion (A): Nichrome is used as a heating element in electrical appliances.
Reason (R): Nichrome has low resistivity and gets cooled quickly.

✅ Answer: C
Explanation: The assertion is true, but the reason is false. Nichrome has high resistivity and remains hot for a longer time, making it suitable as a heating element.

Q4.
Assertion (A): Immersion rods and geysers are examples of heating appliances.
Reason (R): These devices are used to cool down electrical circuits.

✅ Answer: C
Explanation: The assertion is true, but the reason is false. These appliances are used for heating, not cooling.

Q5.
Assertion (A): In heating appliances, heat generated is directly proportional to the resistance of the wire.
Reason (R): Heat is given by the formula $H = I^2Rt$

✅ Answer: A
Explanation: Both statements are true and the reason correctly explains the assertion. Heat increases with resistance, current squared, and time.

🔧 Worksheet: Heating Effect of Electric Current

📘 Subject: Science (Physics)

📚 Chapter: Electricity

🧠 Topic: Conversion of Electrical Energy into Heat Energy

🎯 Level: Class 10 / CBSE Board / JEE, NEET Competitive Exams

✍️ Section A: Fill in the Blanks

1. __________ wire is commonly used as a heating element in electrical appliances.
2. An electric fan becomes slightly warm because a small amount of electric energy is converted into __________.
3. The heating element of an electric iron has a __________ resistance.
4. Electrical energy is mainly converted into __________ in an electric heater.
5. Devices like electric heaters and geysers work on the __________ effect of electric current.

✅ Section B: True or False

1. All electrical appliances convert electric energy completely into heat energy.
2. The heating effect of current is used in electric bulbs and geysers.
3. Nichrome has low resistance and hence is not suitable as a heating element.
4. An electric fan is an example of an electrical heating appliance.
5. High resistance in a heating element leads to more heat generation.

💡 Section C: Match the Following

🧮 Section D: Answer in One Line

1. Why does an electric heater become hot very quickly?
2. What is the function of a heating coil in appliances like geysers?
3. Name two electrical appliances that use the heating effect of current.
4. What kind of wire is used in the heating element of electric appliances?
5. Why does an electric fan get only slightly warm?

📝 Section E: Short Answer Questions

1. Why do some appliances convert most electrical energy into heat, while others do not?
2. What role does resistance play in heat generation in electric appliances?
3. Explain why an electric iron uses a coil made of nichrome.
4. What happens when electric current passes through an immersion rod?

🔍 Section F: HOTS (Higher Order Thinking Skills)

1. A student uses a copper wire instead of nichrome in an electric heater. What will happen and why?
2. How does the principle of energy conservation apply to the working of a geyser?

🧠 Section G: Assertion-Reason Type Question (One Sample)

Assertion: Electric fans do not get hot like heaters.
Reason: Fans convert electrical energy mostly into mechanical energy.
Options: A. Both A and R are true, and R is the correct explanation of A
B. Both A and R are true, but R is not the correct explanation of A
C. A is true, R is false
D. A is false, R is true

📌 Quick Revision

🧠 Do You Know?

• Nichrome is preferred in heaters because of its high resistance and durability.
• Tungsten is used in bulbs due to its high melting point.
• A glowing bulb filament reaches temperatures around 2500°C!
• Electric fuses save lives—they prevent fires during short circuits.