Electric Current and Its Effects Class 7 Questions with Answers Explained

Understanding Electric Current: Definition and Basics

Electric current is the flow of electric charge through a conductor, usually measured in amperes (A). In Class 7 NCERT science, electric current is introduced as the movement of electrons in a wire when connected to a battery or power source.

• Definition: Electric current is the rate of flow of charge.
• Unit: Ampere (A)
• Direction: Conventional current flows from positive to negative terminal.

Formula:

$$I = \frac{Q}{t}$$

where $I$ is current, $Q$ is charge in coulombs, and $t$ is time in seconds.

Understanding this basic concept is essential before exploring the effects of electric current.

Effects of Electric Current: Heating, Magnetic, and Chemical

Electric current produces different effects when it flows through a conductor. These effects are important for practical applications and are covered in Class 7 NCERT.

1. Heating Effect: When current passes through a wire, it heats up. This is used in electric bulbs, heaters, and fuses. 2. Magnetic Effect: Current flowing through a wire creates a magnetic field around it. This principle is used in electromagnets and electric bells. 3. Chemical Effect: Electric current can cause chemical changes, such as in electroplating and electrolysis.

These effects show how electric current is useful in daily life and technology.

Ohm’s Law and Its Application in Class 7 Science

Ohm’s Law is a fundamental concept that relates voltage ($V$), current ($I$), and resistance ($R$) in an electrical circuit:

$$V = IR$$

• $V$ is the voltage across the conductor in volts (V).
• $I$ is the current through the conductor in amperes (A).
• $R$ is the resistance of the conductor in ohms (Ω).

Example: If a wire has a resistance of 5 Ω and a current of 2 A flows through it, the voltage across it is:

$$V = 2 \times 5 = 10\text{ volts}$$

Ohm’s Law helps solve many Class 7 questions related to electric circuits.

Comparing Conductors and Insulators in Electric Circuits

Materials used in electric circuits are classified as conductors or insulators based on their ability to allow electric current.

Understanding this difference helps in answering questions about circuit safety and design.

Safety Measures and Devices in Electric Circuits

Electric current can be dangerous if not controlled. Class 7 NCERT includes safety devices that protect circuits and users:

• Fuse: A wire that melts if current is too high, breaking the circuit.
• Circuit Breaker: Automatically switches off the circuit during overload.
• Earthing: Provides a path for excess current to flow safely to the ground.

These devices prevent accidents and damage, making electric current safe to use.

Solved Examples: Practice Questions with Answers

Example 1: A current of 3 A flows through a wire for 4 seconds. Calculate the charge that passes through the wire.

Solution: Using $I = \frac{Q}{t}$,

$$Q = I \times t = 3 \times 4 = 12\text{ coulombs}$$

Example 2: If a bulb has a resistance of 10 Ω and the voltage across it is 220 V, find the current flowing through it.

Solution: Using $V = IR$,

$$I = \frac{V}{R} = \frac{220}{10} = 22\text{ amperes}$$

Practicing such questions strengthens your understanding and prepares you for exams.