NCERT Class 7 Science Chapter 10 on Electric Current and its Effect helps us understand some of the essential daily phenomena around us. We start by learning about electric components and their symbols. Following this, we get to know about electric circuits and electric charge. Further, we walk through important concepts of the “heating effect of electric current”. Additionally, we explore the “magnetic effects of electric current”, followed by “electromagnet” and the working of an electric bell. Let us begin!!
This Blog Includes:
- Electric Components and Their Symbols
- Electric Charge
- Heating Effect of Electric Current
- Magnetic Effect of Electric Current
- Working of Electric Bell
- NCERT Solutions Class 7 Science Chapter 10: Electric Current and its Effect
Electric Components and Their Symbols
An electric circuit consists of the following components:
- Electric cell
- Electric bulb
- Cell holder
Symbols of Electric Components
Let us now look at the symbols of the aforementioned electric components:
Now that we are familiar with the symbols of electric components, let us look at the pictorial representation of an electric circuit:
One of the fundamental physical properties of matter which enables it to experience a unique type of force when placed within an electromagnetic field is known as its “electric charge”.
Here are some properties of electric charge:
- There are two types of electric charges- Positive and Negative.
- Unlike electric charges attract each other. Whereas, similar charges repel each other.
- SI unit of electric charge: Coulomb. As 1 Coulomb= 6.242×1018 e, the value of 1 electron= −1.602×10-19 C
Heating Effect of Electric Current
Furthermore, NCERT Class 7 Science Chapter 10 explains to us about conductors and insulators. Also, the lesson deals with the heating effect of electric current. Also, we get to learn about electric bulbs and electric fuse.
Conductors and Insulators
- Conductors: Materials or substances that facilitate the flow of electric current and offer less resistance to their flow are known as “conductors”. For instance, water, iron, copper, etc.
- Insulators: Materials or substances that hinder the flow of electric current are known as “insulators”. For instance, sand, rubber, wood, etc.
Heating Effects of Electric Current
The flow of electricity through a wire generates heat, a phenomenon known as the “heating effect of electric current.” The quantity of heat generated in the wire is influenced by factors like
- Type of material
- Thickness of material
- Length of material
When a substantial electric current flows through the wire, it can become so hot that it might even melt and snap. This principle of electrical heating is harnessed in various household devices like electric heaters, toasters, and water heaters. Additionally, it is applied in light bulbs and as a protective mechanism, as seen in fuses.
Electric Bulb and Electric Fuse
Based on the heating effects of electric current, there are two important appliances that we must know about. These appliances are- electric bulbs and electric fuse. Both these use the “heating effect of electric current” to function.
- Electric Bulb: The filament inside an electric bulb becomes so hot that it reaches a high temperature, causing it to emit light and glow.
- Electric Fuse: Wires composed of specific materials have the unique property of rapidly melting and breaking when subjected to high electric currents. These specialised wires are used in the construction of electric fuses. Fuses are installed in all electrical circuits within buildings. They serve as a safeguard, as they have a maximum threshold for the current that can safely traverse a circuit. Therefore, in case of an overflow of electric current beyond this safe limit, the wires may overheat and potentially lead to a fire. When a proper fuse is installed in the circuit, it will blow and disconnect the circuit. Therefore, an “electric fuse” functions as a safety device, preventing damage to electrical circuits and the occurrence of potential fires.
Magnetic Effect of Electric Current
When an electric current flows through a wire, it exhibits magnetic properties. This is referred to as the magnetic effect of electric current. In essence, an electric current has the capability to create magnets or induce magnetism in materials.
This was first discovered by a scientist named Hans Christian Orested. He discovered the magnetic effect of electric current by noticing the deflection of a compass needle when electric current was transmitted through it.
Let us look at how a compass needle reacts when an electric current is passed through it.
Lightning and Magnetism
Furthermore, in the Magnetic Effect and Electric Current section of the NCERT Class 7 Science Chapter 10, we also learn about lighting and magnetism. Let’s start!!
- During thunderstorms, upward air currents and downward-moving water droplets lead to the division of electrical charges, creating disparities between clouds and between clouds and the Earth.
- As the amount of electric charge intensifies, even the typically poor conductor, air, begins to conduct electricity, leading to what we recognize as lightning. This discharge of charge is accompanied by brilliant flashes of light and the accompanying sound.
- Lightning also gives rise to naturally occurring magnets known as lodestones.
Explore More: Magnetic Effects Of Electric Current Class 10
An artificial magnet that emits a magnetic field around a conductor on account of the transmission of electric current through it is known as an “electromagnet.” In such magnets, the magnetic field disappears when the electric current does not pass through the conductor.
Working of Electric Bell
An electric bell comprises an electromagnet that uses a switch to complete the circuit. Let us now explore the working of an electric bell:
- As soon as we press the switch, it initiates the flow of electric current within the circuit.
- Thereafter, the electromagnet is energized. Due to this, a magnetic field is generated that pulls the iron strip toward it.
- Now, the striker comes into contact with the gong or bell, producing a striking sound.
- When the striking arm hits the gong, it separates the contact point, interrupting the current flow in the circuit. This leads to the demagnetization of the electromagnet.
- A connected spring arm restores the striker to its original resting position. With the restoration of connection, the contact is reestablished, enabling current to flow through the circuit again (assuming the main switch is still pressed).
- Finally, a repetition of this sequence of events occurs until the switch is opened.
Also Read: Class 12 Physics Current Electricity Notes
NCERT Solutions Class 7 Science Chapter 10: Electric Current and its Effect
In this section, we will explore solutions to writing questions in Class 7 Science Chapter 10 on Electric Current and its Effect.
Ques 4: The bulb in the circuit shown in Fig.10.23 does not glow. Can you identify the problem? Make necessary changes in the circuit to make the bulb glow.
Ans: The bulb glows when we switch the two electric cells to connect opposite charges and make electricity flow.
Ques 5. Name any two effects of electric current.
Ans: Here are two effects of electric current:
- Heating effect of electric current
- Magnetic effect of electric current
Ques 6. When the current is switched on through a wire, a compass needle kept nearby gets deflected from its north-south position. Explain.
Ans: When an electric current is switched on through a wire, a magnetic field is created around the wire. This magnetic field will deflect the compass needle from its north-south position.
Ques 7: Will the compass needle show deflection when the switch in the circuit shown in the following diagram?
Ans: No, the compass needle remains unaffected when the circuit is closed, and the magnetic field only forms when electric current flows through the circuit.
Ques 8. Fill up the blanks:
a. Longer line in the symbol for a cell represents its__________ terminal.
b. The combination of two or more cells is called a____________.
c. When current is switched ‘on’ in a room heater, it_______________.
d. The safety device based on the heating effect of electric current is called a ______________.
c. Produces heat
Ques 9. Which of the following statements are True or False?
a. To make a battery of two cells, the negative terminal of one cell is connected to the negative terminal of the other cell.
b. When the electric current through the fuse exceeds a certain limit, the fuse wire melts and breaks.
c. An electromagnet does not attract a piece of iron.
d. An electric bell has an electromagnet.
Ques 10. Do you think an electromagnet can be used for separating plastic bags from a garbage heap? Explain.
Ans: No, an electromagnet cannot be used for separating plastic bags from a garbage heap because plastic bags do not have magnetic properties.
Ques 11. An electrician is carrying out some repairs in your house. He wants to replace a fuse with a piece of wire. Would you agree? Give reasons for your response.
Ans: It is not advisable to substitute a fuse with a wire given that fuses have a very low melting point. Whereas, using a metal piece with a higher melting point ensures the circuit remains undisturbed in situations of overloading or excessive heat.
Ques 12. Zubeda made an electric circuit using a cell holder shown in the below diagram, a switch, and a bulb. When she put the switch in the ‘ON’ position, the bulb did not glow. Help Zubeda identify the possible defects in the circuit.
Ans: Here are some possible reasons for defects in the circuit:
- Loose connecting wires
- Defective electric cells
- Defects in switch
Ques 13. In the circuit shown below:
(i) Would any of the bulbs glow when the switch is in the ‘OFF’ position?
(ii) What will be the order in which the bulbs A, B and C will glow when the switch is moved to the ‘ON’ position?
(i) No, the bulb will not glow because the electric circuit is incomplete when the switch is turned ‘OFF’.
(ii) If the switch is turned ‘ON’, the bulb will glow.
Q1. What is an electromagnet?
Ans: An artificial magnet that emits a magnetic field around a conductor on account of the transmission of electric current through it is known as an “electromagnet.”
Q2. What is an electric charge?
Ans: One of the fundamental physical properties of matter which enables it to experience a unique type of force when placed within an electromagnetic field is known as its “electric charge”.
Q3. What are the components of an electric circuit?
Ans: Here are the different electric components:
- Electric cell
- Electric bulb
- Cell holder
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