Grade 10 Chapter 4: Effects of Electric Current

Introduction

Electric current is the flow of electric charge through a conductor. When electric current flows through a conductor, it produces various effects that have numerous practical applications in our daily lives. This chapter explores the thermal, magnetic, and chemical effects of electric current, along with their applications in devices and technologies that we use regularly.

Thermal Effect of Electric Current

Heating Effect of Electric Current

When electric current passes through a conductor, the conductor becomes hot. This is known as the heating effect or thermal effect of electric current.

Explanation of the Heating Effect

The heating effect occurs due to the conversion of electrical energy into heat energy. When electric current flows through a conductor, the free electrons move through the conductor and collide with the atoms or ions of the conductor. These collisions transfer energy to the atoms, increasing their vibrational energy, which we perceive as heat.

The amount of heat produced in a conductor depends on: 1. The resistance of the conductor (R) 2. The current flowing through the conductor (I) 3. The time for which the current flows (t)

This relationship is given by Joule's law of heating: H = I²Rt

Where: - H is the heat produced in joules (J) - I is the current in amperes (A) - R is the resistance in ohms (Ω) - t is the time in seconds (s)

Factors Affecting the Heating Effect

1. Current: The heat produced is directly proportional to the square of the current. Doubling the current increases the heat produced by four times.

2. Resistance: The heat produced is directly proportional to the resistance. Materials with higher resistance produce more heat for the same current.

3. Time: The heat produced is directly proportional to the time for which the current flows.

Applications of the Heating Effect

The heating effect of electric current has numerous practical applications:

1. Electric Heating Appliances

• Electric Iron: Contains a heating element made of high-resistance wire that gets hot when current passes through it.
• Electric Toaster: Uses nichrome wire as a heating element to toast bread.
• Electric Kettle: Has a heating element at the bottom that heats water.
• Room Heater: Contains coils of high-resistance wire that produce heat when current flows.
• Water Heater (Geyser): Uses immersion heaters to heat water.

2. Electric Bulbs

• Incandescent Bulbs: Contain a tungsten filament that gets heated to high temperatures (about 2700°C) and emits light.
• Halogen Lamps: Use a tungsten filament enclosed in a small quartz envelope filled with halogen gas.

3. Electric Fuse

An electric fuse is a safety device that protects electrical circuits and appliances from damage due to excessive current. It consists of a wire or strip of a low melting point metal (like tin-lead alloy) that melts and breaks the circuit when the current exceeds a safe value.

Working principle: - When the current exceeds the rated value, the fuse wire heats up and melts. - This breaks the circuit and prevents damage to the appliances. - The fuse wire must have a lower melting point than the wires in the circuit.

Types of fuses: - Cartridge fuse: Used in household appliances - HRC (High Rupturing Capacity) fuse: Used in industrial applications - Rewirable fuse: Common in household distribution boards

Magnetic Effect of Electric Current

Magnetic Field Around a Current-Carrying Conductor

When electric current flows through a conductor, it creates a magnetic field around the conductor. This was first discovered by Hans Christian Oersted in 1820.

Straight Conductor

For a straight current-carrying conductor: - The magnetic field consists of concentric circles around the conductor. - The direction of the magnetic field can be determined using the Right-Hand Thumb Rule: - If you hold the conductor in your right hand with your thumb pointing in the direction of the current, your fingers will curl in the direction of the magnetic field.

Circular Loop

For a circular current-carrying loop: - The magnetic field lines are circular near the wire. - At the center of the loop, the magnetic field is perpendicular to the plane of the loop. - The strength of the magnetic field at the center depends on: - The current in the loop - The radius of the loop - The number of turns in the loop

Solenoid

A solenoid is a coil of wire wound in the form of a helix. When current flows through a solenoid: - The magnetic field inside the solenoid is uniform and parallel to its axis. - The magnetic field outside the solenoid is similar to that of a bar magnet. - One end of the solenoid behaves as a north pole and the other end as a south pole. - The strength of the magnetic field depends on: - The current in the solenoid - The number of turns per unit length - The presence of a core material (like iron)

Electromagnet

An electromagnet is a solenoid with a soft iron core. The soft iron core increases the strength of the magnetic field significantly.

Characteristics of electromagnets: - The magnetic field can be turned on or off by controlling the current. - The strength of the magnetic field can be varied by changing the current. - The polarity can be reversed by reversing the direction of the current.

Applications of electromagnets: - Electric bells: Use an electromagnet to strike a bell when current flows - Loudspeakers: Convert electrical signals into sound using an electromagnet - Magnetic cranes: Lift heavy magnetic materials using powerful electromagnets - MRI machines: Use strong electromagnets for medical imaging - Magnetic levitation trains: Use electromagnets for propulsion and levitation

Electric Motors

An electric motor is a device that converts electrical energy into mechanical energy. It works on the principle that a current-carrying conductor placed in a magnetic field experiences a force.

Working Principle

1. When a rectangular coil is placed in a magnetic field and current is passed through it, the coil experiences a force due to the magnetic field.
2. This force causes the coil to rotate.
3. A split-ring commutator reverses the direction of current in the coil every half rotation, ensuring continuous rotation in one direction.

Construction of a Simple DC Motor

A simple DC motor consists of: 1. Armature: A rectangular coil wound around a soft iron core 2. Field Magnet: Permanent magnets or electromagnets that provide a magnetic field 3. Commutator: Split rings that reverse the current direction in the armature 4. Brushes: Carbon brushes that maintain contact with the commutator 5. Axle: Supports the armature and allows it to rotate

Applications of Electric Motors

• Household appliances: Fans, mixers, washing machines, refrigerators
• Industrial machinery: Pumps, compressors, conveyor belts
• Transportation: Electric vehicles, trains, trams
• Toys and gadgets: Remote-controlled cars, drones

Chemical Effect of Electric Current

Electrolysis

Electrolysis is the process of chemical decomposition of an electrolyte by passing electric current through it.

Components of Electrolysis

1. Electrolyte: A solution or molten substance that conducts electricity due to the presence of ions
2. Electrodes: Conductors (usually metals) that connect the electrolyte to the external circuit
3. Anode: Positive electrode where oxidation occurs
4. Cathode: Negative electrode where reduction occurs
5. Battery or DC source: Provides the electrical energy for the process

Process of Electrolysis

1. When electrodes are connected to a battery and placed in an electrolyte:
2. Positive ions (cations) move towards the cathode
3. Negative ions (anions) move towards the anode
4. At the cathode, cations gain electrons (reduction)
5. At the anode, anions lose electrons (oxidation)
6. These redox reactions lead to chemical changes in the electrolyte

Applications of Electrolysis

1. Electroplating

Electroplating is the process of coating one metal with another using electrolysis. It is used to: - Protect metals from corrosion - Improve appearance - Increase durability - Reduce friction

Process of electroplating: 1. The object to be plated is made the cathode 2. A piece of the plating metal is used as the anode 3. A solution containing ions of the plating metal serves as the electrolyte 4. When current flows, metal ions from the electrolyte are deposited on the cathode

Examples: - Silver plating of cutlery - Chromium plating of car parts - Gold plating of jewelry - Zinc plating (galvanizing) of iron to prevent rusting

2. Electrorefining

Electrorefining is the process of purifying metals using electrolysis.

Process: 1. The impure metal is made the anode 2. A thin sheet of pure metal is used as the cathode 3. A solution containing ions of the metal serves as the electrolyte 4. When current flows, pure metal from the anode dissolves into the solution and gets deposited on the cathode

Example: Copper refining - Impure copper (anode) → Cu²⁺ ions in solution → Pure copper (cathode) - Impurities either dissolve in the solution or fall as "anode mud"

3. Electrometallurgy

Electrometallurgy is the extraction of metals from their ores using electrolysis.

Example: Extraction of aluminum from bauxite 1. Bauxite is converted to alumina (Al₂O₃) 2. Alumina is dissolved in molten cryolite (Na₃AlF₆) 3. Electrolysis is carried out with carbon anodes and a carbon-lined steel tank as the cathode 4. Aluminum is deposited at the cathode

4. Electrolytic Cells and Batteries

• Primary cells: Convert chemical energy to electrical energy (non-rechargeable)

• Example: Dry cell (zinc-carbon cell)

• Secondary cells: Can be recharged by passing current in the opposite direction

• Example: Lead-acid battery used in vehicles

Domestic Electric Circuits

Components of a Domestic Electric Circuit

1. Main supply: Provides electricity to the house (typically 220-240V in India)
2. Main fuse: Protects the entire circuit from excessive current
3. Electricity meter: Measures the electrical energy consumed
4. MCB (Miniature Circuit Breaker): Modern alternative to fuses that can be reset
5. Distribution board: Divides the supply into different circuits
6. Earth connection: Safety feature that provides a path for leakage current

Wiring in Domestic Circuits

Domestic wiring typically uses three wires: 1. Live wire (Red or Brown): Carries current from the supply to the appliance 2. Neutral wire (Black or Blue): Completes the circuit by carrying current back to the supply 3. Earth wire (Green or Yellow-Green): Safety wire connected to the metal body of appliances

Electric Power and Energy

Electric Power

Power is the rate at which electrical energy is consumed or work is done.

P = VI = I²R = V²/R

Where: - P is power in watts (W) - V is voltage in volts (V) - I is current in amperes (A) - R is resistance in ohms (Ω)

Electric Energy

Energy is the total electrical work done or energy consumed over a period of time.

E = P × t = VI × t = I²R × t

Where: - E is energy in joules (J) or watt-hours (Wh) - P is power in watts (W) - t is time in seconds (s) or hours (h)

Commercial unit of electrical energy: kilowatt-hour (kWh) 1 kWh = 1000 Wh = 3.6 × 10⁶ J

Electrical Safety Measures

1. Proper insulation: All electrical wires should be properly insulated
2. Earthing: All electrical appliances with metal bodies should be properly earthed
3. Use of fuses and MCBs: To protect circuits from overloading
4. Double insulation: Modern appliances have double insulation for extra safety
5. ELCB (Earth Leakage Circuit Breaker): Detects small leakage currents and breaks the circuit
6. Avoiding water contact: Keeping electrical appliances away from water
7. Regular maintenance: Checking for worn-out insulation or loose connections

Summary

Electric current produces three main effects:

1. Thermal Effect: Conversion of electrical energy to heat energy

2. Applications: Electric heating appliances, bulbs, fuses

3. Magnetic Effect: Creation of magnetic field around current-carrying conductors

4. Applications: Electromagnets, electric motors, generators

5. Chemical Effect: Chemical changes due to the passage of electric current through electrolytes

6. Applications: Electroplating, electrorefining, electrometallurgy, batteries

Understanding these effects and their applications helps us appreciate the importance of electricity in our daily lives and the functioning of various electrical devices and systems.

Practice Questions

1. Explain Joule's law of heating. How does the heat produced depend on current, resistance, and time?

2. Why are heating elements in electrical appliances made of high-resistance materials like nichrome?

3. Describe the working principle of an electric fuse. Why is it an important safety device?

4. State the Right-Hand Thumb Rule for finding the direction of the magnetic field around a current-carrying conductor.

5. Compare the magnetic field patterns for a straight conductor, a circular loop, and a solenoid carrying current.

6. Explain the construction and working of a simple DC motor.

7. What is electrolysis? Explain the process with a suitable example.

8. Describe the process of electroplating with the help of a labeled diagram.

9. Calculate the electrical energy consumed when a 1000 W appliance is used for 5 hours.

10. What safety measures should be taken while handling electrical appliances?

References: 1. Maharashtra State Board 10th Standard Science Syllabus 2025-26 2. NCERT Science Textbook for Class 10 3. Electricity and Magnetism - Concepts and Applications 4. Practical Applications of Electrical Effects - Modern Perspective