CBSE Notes Class 7 Science Chapter 10 - Electric Current And Its Effects

Electric current is essential for grasping how electricity functions in our daily lives. In simple terms, it recommends movement of  charge through a conductor, such as a wire. This flow is primarily driven by the movement of electrons, which are tiny particles within atoms. Additionally, understanding the effects of electric current highlights the importance of safety measures.

1.0Electric Current

• It arises due to  the movement of electric charge transferred by moving electrons in a wire. It is measured as the rate of flow of charge, with the SI unit being the Ampere (A). An ammeter measures this current, denoted by the symbol I
• Initially, it was thought that current flowed from the positive to the negative endpoint of a battery, but it actually flows from negative to positive. Nonetheless, the conventional direction is still considered to be from positive to negative.

2.0Applications Of Electric Current

1. Electrical Appliances: Used in refrigerators, fans, TVs, bulbs, and tube lights.
2. Batteries: Power devices like cameras, remotes, and mobile phones.
3. Electronic Components: Essential for computer chips.
4. Electromagnets and Electrochemistry: Key in various industrial applications.

3.0Hazards Of Electric Current

• Touching an open wire carrying electricity or a plugged-in switch can lead to the flow of electric charge through the human body, resulting in an electric shock. This can cause pain, temporary or permanent burns, cardiac arrest, or even death. Similarly, lightning strikes can produce effects akin to an electric shock.
• Additionally, prolonged exposure to electromagnetic waves from sources like mobile signals and Wi-Fi may impact the human nervous system.

4.0Cell And Batteries

5.0Electrical Components And Symbols

6.0Electric Circuit

• An electric circuit is a pathway for the flow of electrons (or current). If the circuit is incomplete or broken, current cannot flow, resulting in what is called an open circuit. Conversely, when the circuit is complete, current flows, creating a closed circuit. 
• If the circuit includes materials that do not allow current to pass through, it will also prevent the flow of current, even if the circuit is closed. These materials are known as non-conductors.
• Typically, a circuit consists of a power source, which provides electrons, and a load, such as a bulb, that requires electricity to operate. A switch or key in the circuit is used to open or close the circuit, controlling the flow of current. 

7.0Circuit Diagram

• Electric circuits are often illustrated using circuit diagrams.

8.0Heating Effects Of Electric Current

1. When electric current glides through a conductor, it generates heat due to the resistance encountered. Appliances that utilize the heating effect are equipped with conductors or heating elements designed for this purpose. 
2. These heating elements have a high melting point to prevent damage from the heat produced and are also resistant to oxidation to minimize the risk of catching fire. 
3. The amount of heat generated in a wire depends on several factors:

•  The material of the wire
• The length of the wire
• The thickness of the wire

9.0Applications Of Heating Effects Of Electric Current

• Electric Geyser
• Water Heating Rod
• Iron Press

10.0Electric Fuse And Circuit Breakers

• A fuse or circuit breaker is a safety device that protects appliances from overcurrent or overload, positioned in the circuit after the power source and before the appliance. 
• Fuses consist of a low-resistance wire that melts under excessive current, breaking the circuit to prevent damage and fire hazards. Common causes of excessive current include short circuits (when wires touch directly or due to water) and overloads (when too many devices are connected to one socket).
• Each fuse has a maximum current and voltage rating, so it's crucial to select the right one for the appliance. Using a fuse with too low a rating can cause frequent interruptions, while one with too high a rating may not blow in a minor overload, risking damage.
• A Miniature Circuit Breaker (MCB) automatically shuts off when current exceeds a safe limit, a process called tripping. Unlike fuses, MCBs do not contain wire and rely on the heating effect of current. While fuses must be replaced after blowing, MCBs can be reset like a regular switch to resume operation.

11.0Magnetic Effect Of Current

• When electric current glides through a wire, it creates a magnetic field, known as the electromagnetic effect. This phenomenon was discovered by Hans Christian Oersted in 1820.
• A compass, which resembles a small watch, indicates direction by utilizing the Earth's magnetic field. Its needle acts as a tiny magnet, always aligning itself with the North-South direction. 
• When a compass is brought near a magnet or a current-carrying circuit, the needle deflects due to the magnetic field produced by both. If the direction of the current is reversed, the magnetic field also reverses.

12.0Electromagnet

• It is a magnet whose magnetic field is generated by electric current, and it disappears when the current is turned off. Electromagnets typically consist of many tightly wound turns of wire around a magnetic core made from materials like iron.
• The main advantage of electromagnets over permanent magnets is their controllable magnetic field, which can be turned on and off. However, they require a continuous power supply.
• Common examples of electromagnets in daily life include induction cooktops, electric bells, hard disk drives, loudspeakers, and motors.

13.0Electric Bell

• An electric bell consists of a coil of wire wound around an iron core, an iron armature with an attached hammer, a contact screw, a battery, and a switch.
• When the switch is turned on, electric current flows through the coil, making the iron core act as an electromagnet. This attracts the hammer, which strikes the bell, producing sound. As the hammer moves, it pulls away from the contact screw, breaking the circuit. 
• With the circuit broken, the current stops, causing the electromagnet to lose its magnetic effect and the hammer to return to its original position. The hammer then reconnects with the contact screw, completing the circuit again, and the process repeats until the switch is turned off, resulting in continuous ringing.