Maharashtra Board Class 8 Science Chapter 4 Current Electricity and Magnetism Solutions

Std 8 Science Chapter 4 Current Electricity And Magnetism Question Answer Maharashtra Board

Class 8 Science Chapter 4 Current Electricity And Magnetism Question Answer Maharashtra Board

Question 1. Write proper words from the following group of words in the blanks and rewrite the completed sentences:
(magnetism, 4.5V, 3.0V, gravitational attraction, potential difference, potential, higher, lower, 0V)

Question a. Water in the waterfall flows from a higher level to the lower level because of ..........
Answer: Water in the waterfall flows from a higher level to the lower level because of gravitational attraction.
In simple words: Water always moves from a higher position to a lower position due to the pull of gravity, which is called gravitational attraction.

🎯 Exam Tip: Understanding natural phenomena like water flow due to gravitational attraction helps in grasping concepts like potential difference in electricity.

 

Question b. In an electric circuit, electrons flow from a point of potential to the point of .......... potential.
Answer: In an electric circuit, electrons flow from a point of lower potential to the point of higher potential.
In simple words: Electrons, being negatively charged, move towards areas of higher positive charge or less negative charge.

🎯 Exam Tip: Remember the direction of electron flow is opposite to conventional current flow, which goes from higher to lower potential.

 

Question c. The difference between the electrostatic potential of the positive end and the negative end of an electric cell is the .......... of the cell.
Answer: The difference between the electrostatic potential of the positive end and the negative end of an electric cell is the potential difference of the cell.
In simple words: This potential difference is the driving force that pushes electric current through a circuit.

🎯 Exam Tip: Potential difference, also known as voltage, is crucial for current to flow in a circuit.

 

Question d. Three electric cells of potential difference 1.5 V each have been connected as a battery. The potential difference of the battery will be .......... V.
Answer: Three electric cells of potential difference 1.5 V each have been connected as a battery. The potential difference of the battery will be 4.5 V.
In simple words: When cells are connected in series, their individual voltages add up to give the total potential difference of the battery.

🎯 Exam Tip: For cells in series, the total voltage is the sum of individual cell voltages.

 

Question e. An electric current flowing in a wire creates .......... around the wire.
Answer: An electric current flowing in a wire creates magnetism around the wire.
In simple words: This phenomenon is known as the magnetic effect of electric current, a fundamental concept in electromagnetism.

🎯 Exam Tip: Oersted's discovery of current-induced magnetism is a key concept; remember that moving charges produce magnetic fields.

 

Question 2. A battery is to be formed by joining 3 dry cells with connecting wires. Show how you will connect the wires by drawing a diagram.

Question a. A battery is to be formed by joining 3 dry cells with connecting wires. Show how you will connect the wires by drawing a diagram.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र तीन शुष्क सेलों को श्रृंखला में जोड़ने का तरीका दर्शाता है। प्रत्येक सेल का धनात्मक टर्मिनल अगले सेल के ऋणात्मक टर्मिनल से जुड़ा होता है, जिससे एक बैटरी बनती है। यह व्यवस्था कुल वोल्टेज को बढ़ाने के लिए की जाती है।
In simple words: To form a battery from multiple cells, connect the positive terminal of one cell to the negative terminal of the next in a series, which sums up their voltages.

🎯 Exam Tip: When connecting cells in series to form a battery, ensure the positive terminal of one cell connects to the negative terminal of the next for additive voltage.

 

Question 3. In an electric circuit, a battery and a bulb have been connected and the battery consists of two cells of equal potential difference. If the bulb is not glowing, then which tests will you perform in order to find out the reason for the bulb not glowing?

Question a. In an electric circuit, a battery and a bulb have been connected and the battery consists of two cells of equal potential difference. If the bulb is not glowing, then which tests will you perform in order to find out the reason for the bulb not glowing?
Answer: If you can see the filament of the bulb, check whether it is intact or broken. Check whether the cells are connected in a proper manner:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र सही तरीके से जुड़े हुए दो सेलों को दिखाता है, जहाँ एक सेल का धनात्मक सिरा दूसरे सेल के ऋणात्मक सिरे से जुड़ा है, जिससे कुल विभव अंतर जुड़ जाता है।
Or in a wrong way:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र गलत तरीके से जुड़े हुए दो सेलों को दिखाता है, जहाँ एक सेल का धनात्मक सिरा दूसरे सेल के धनात्मक सिरे से जुड़ा है, जिससे विभव अंतर शून्य हो जाता है।
If they are connected in a wrong way as shown above, the total potential difference will be 2V + (-2V) = zero.
Figures for reference:
ℹ️ चित्र व्याख्या (Diagram Explanation): चित्र (a) एक साधारण परिपथ दिखाता है जिसमें एक सेल, एक बल्ब और इलेक्ट्रॉनों का प्रवाह दर्शाया गया है, जबकि चित्र (b) श्रृंखला में जुड़े चार सेलों की एक बैटरी दिखाता है, जो कुल 6V का विभव अंतर प्रदान करती है।
In simple words: To troubleshoot a non-glowing bulb, first check the bulb's filament for breakage, then inspect the battery's cell connections to ensure they are properly aligned in series, not opposing each other.

🎯 Exam Tip: Common reasons for circuit failure include broken filaments, loose connections, or incorrect cell polarity, so systematic checking is essential.

 

Question 4. Electric cells having potential difference 2V each have been connected in the form of a battery. What will be the total potential difference of the battery in both cases?
(i)
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र तीन विद्युत सेलों को श्रृंखला में जुड़ा हुआ दिखाता है, जहाँ प्रत्येक सेल 2V का विभव अंतर प्रदान करता है, जिससे कुल विभव अंतर 6V होता है।
(ii)
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र चार विद्युत सेलों को श्रृंखला में जुड़ा हुआ दिखाता है, जहाँ प्रत्येक सेल 2V का विभव अंतर प्रदान करता है, जिससे कुल विभव अंतर 8V होता है।
Answer:
(i) 6V
(ii) 8V.
[Note: In (i), three cells are connected in series.

Total potential difference = 2V + 2V + 2V = 6V.
In (ii), four cells are connected in series.

Total potential difference = 2V + 2V + 2V + 2V
= 8 V]
In simple words: For cells connected in series, the total potential difference is simply the sum of the individual potential differences of each cell.

🎯 Exam Tip: Always add the voltages when cells are connected in series to find the total potential difference of the battery.

 

Question 5. Describe the construction, working and usefulness of a dry cell, with the help of a diagram.

Question a. Describe the construction, working and usefulness of a dry cell, with the help of a diagram.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक शुष्क सेल की आंतरिक संरचना को दर्शाता है, जिसमें एक धनात्मक कार्बन इलेक्ट्रोड, एक ऋणात्मक जिंक आवरण, इलेक्ट्रोलाइट पेस्ट, और मैंगनीज डाइऑक्साइड का मिश्रण होता है, जो विद्युत धारा उत्पन्न करने के लिए रासायनिक प्रतिक्रियाएँ करता है।
Dry cell:
Take a lead dry cell and remove its outer coating. Inside you will find a whitish, metal layer. This is the zinc (Zn) metal layer. This is the negative terminal of the cell. Now, carefully break open this layer. There is another layer inside. An electrolyte is filled between these two layers.
The electrolyte contains negatively charged and positively charged ions. These are the carriers of electricity. The electrolyte is a wet pulp of zinc chloride (ZnCl2) and ammonium chloride (NH4Cl). There is a graphite rod at the centre of the cell. This is positive terminal of the cell. A paste of manganese dioxide (MnO2) is filled outside the rod. Because of the chemical reactions of all these chemicals, electrical charge is produced on the two terminals (graphite rod and zinc layer) and an electric current flows in the circuit.
Due to the wet pulp used in this cell, the chemical reaction proceeds very slowly. Hence a large electric current cannot be obtained from this. Compared to the electric cells using liquids, the shelf life of dry cells is longer. Dry cells are very convenient to use as these can be held in any direction with respect to ground and can be used in mobile instruments such as radio sets, wall clocks and torches.
In simple words: A dry cell converts chemical energy into electrical energy using a zinc container (negative terminal), a carbon rod (positive terminal), and an electrolyte paste, making it compact and portable for various devices.

🎯 Exam Tip: When describing a dry cell, highlight its main components (zinc casing, carbon rod, electrolyte, manganese dioxide) and its advantage of portability due to its paste-like electrolyte.

 

Question 6. Describe the construction and working of an electric bell with the help of a diagram.

Question a. Describe the construction and working of an electric bell with the help of a diagram.
Answer: Figure shows the construction of an electric bell and also the electric circuit. The bell consists of an electromagnet, contact screw, iron strip, metal striker and metal gong. A coil of copper wire wound around an iron piece works as an electromagnet and an iron strip along with a striker is fitted near it. A contact screw touches the strip.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक विद्युत घंटी की संरचना और उसके परिपथ को दर्शाता है, जिसमें एक इलेक्ट्रोमैग्नेट, एक स्ट्राइकर के साथ एक लोहे की पट्टी, एक संपर्क पेंच और एक धातु का घंटा शामिल है जो विद्युत प्रवाह के चुंबकीय प्रभाव का उपयोग करके ध्वनि उत्पन्न करता है।
The circuit is closed with the key. The current flows in the circuit when the screw is in contact with the iron strip. The current - carrying coil becomes a magnet and attracts the iron strip towards it. As a result, the metal striker hits the metal gong producing sound. At the same time, the screw loses the contact with the strip. The circuit is now incomplete.
Hence, no current flows in the circuit. Therefore, the electromagnet loses its magnetism and the electric iron strip returns to its initial condition, making contact with the screw. As the circuit is now completed, the electromagnet attracts the iron strip and the striker strikes the gong producing sound.
The action repeats itself and the bell continues to ring till the circuit is broken by opening the key in the circuit.
The working of the electric bell is thus based on the magnetic effect of electric current.
In simple words: An electric bell works on the magnetic effect of current: when current flows, an electromagnet pulls an iron strip, causing a striker to hit a gong, which simultaneously breaks the circuit, stopping the current and resetting the process to ring again.

🎯 Exam Tip: Focus on explaining the cycle of making and breaking the circuit, and how the electromagnet's temporary magnetism causes the striker to hit the gong, for a complete answer.

 

Project: Present all the activities that you performed in this chapter in Science exhibition.

Class 8 Science Chapter 4 Current Electricity And Magnetism Additional Important Questions And Answers

Rewrite The Sentences After Filling The Blanks:

Question 1. The Sl unit of electric charge is the ..........
Answer: The Sl unit of electric charge is the coulomb.
In simple words: Coulomb is the standard unit for measuring electric charge.

🎯 Exam Tip: Remembering SI units like the coulomb for charge is fundamental for physics questions.

 

Question 2. The Sl unit of electric current is the ..........
Answer: The Sl unit of electric current is the ampere.
In simple words: Ampere is the standard unit for measuring electric current, representing the flow rate of charge.

🎯 Exam Tip: The ampere is a base SI unit, crucial for understanding current electricity.

 

Question 3. The Sl unit of electric potential is the ..........
Answer: The Sl unit of electric potential is the volt.
In simple words: Volt is the standard unit for measuring electric potential, which is the potential energy per unit charge.

🎯 Exam Tip: Voltage (potential difference) is the force that drives current; its SI unit is the volt.

 

Question 4. 1 ampere = 1 coulomb per ..........
Answer: 1 ampere = 1 coulomb per second.
In simple words: This equation defines current as the amount of charge flowing per unit time.

🎯 Exam Tip: This relationship is a direct definition of electric current, useful for calculations and conceptual understanding.

 

Question 5. When a glass rod is rubbed on a silk cloth, the glass rod acquires ............... charge.
Answer: When a glass rod is rubbed on a silk cloth, the glass rod acquires positive charge.
In simple words: Rubbing a glass rod with silk causes electrons to transfer from the rod to the silk, leaving the rod positively charged.

🎯 Exam Tip: Remember triboelectric effect examples; glass-silk interaction is a classic for demonstrating positive charge acquisition.

 

Rewrite The Following Statements Selecting The Correct Options:

Question 1. The potential difference between the two electrodes of the lead-acid cell is nearly
(a) 1 V
(b) 1.2 V
(c) 1.5 V
(d) 2 V
Answer: (d) 2 V
In simple words: A single lead-acid cell typically provides a voltage of 2 volts.

🎯 Exam Tip: Knowing the typical voltage of common cells like lead-acid cells (2V) is important for practical applications and exams.

 

Question 2. The Ni-Cd cell delivers a potential difference of
(a) 1 V
(b) 1.2 V
(c) 1.5 V
(d) 2 V
Answer: (b) 1.2 V
In simple words: A Nickel-Cadmium (Ni-Cd) cell generally has a potential difference of 1.2 volts.

🎯 Exam Tip: Be aware of the standard voltages for different types of batteries, such as 1.2V for Ni-Cd cells versus 1.5V for alkaline dry cells.

 

Question 3. .......... is a scalar quantity.
(a) Force
(b) Acceleration
(c) Velocity
(d) Electric current
Answer: (d) Electric current
In simple words: Electric current has magnitude but no specific direction in space, making it a scalar quantity despite its common association with flow direction.

🎯 Exam Tip: Distinguish between scalar quantities (magnitude only, like current) and vector quantities (magnitude and direction, like force, acceleration, and velocity).

 

Question 4. The working of an electric bell is based on ..........
(a) the heating effect of electric current
(b) the chemical effect of electric current
(c) the magnetic effect of electric current
(d) the optical effect of electric current
Answer: (c) the magnetic effect of electric current
In simple words: The electric bell operates by using an electromagnet to create a temporary magnetic field that pulls a hammer to strike a gong.

🎯 Exam Tip: The electric bell is a classic application of the magnetic effect of electric current, demonstrating how electricity can produce mechanical motion.

 

Question 5. The coulomb is the Sl unit of electric ..........
(a) current
(b) resistance
(c) potential
(d) charge
Answer: (d) charge
In simple words: The coulomb quantifies the amount of electric charge, such as the charge carried by many electrons or protons.

🎯 Exam Tip: Ensure you correctly associate SI units with their respective physical quantities (e.g., coulomb with charge, ampere with current, volt with potential).

 

State Whether The Following Statements Are True Or False:

Question 1. The Sl unit of electric potential is the ampere.
Answer: False. (The Sl unit of electric potential is the volt. OR The Sl unit of electric current is the ampere.)
In simple words: This statement is false because the SI unit for electric potential is the volt, while the ampere measures electric current.

🎯 Exam Tip: Carefully differentiate between the units of electric potential (volt) and electric current (ampere) to avoid common mistakes.

 

Question 2. In the external circuit, the conventional current flows from the positive terminal of the cell to the negative terminal of the cell.
Answer: True.
In simple words: Conventional current is defined as flowing from the positive terminal to the negative terminal, opposite to the actual electron flow.

🎯 Exam Tip: Always remember the convention for current direction (positive to negative) as it is widely used in circuit analysis, even if electron flow is the reverse.

 

Question 3. Very small current flows when lightning occurs.
Answer: False. (A large current flows when lightning occurs.)
In simple words: Lightning involves an extremely large and rapid discharge of electric current, not a small one.

🎯 Exam Tip: Lightning is a dramatic example of massive current flow, highlighting the immense power of electrical discharges.

 

Question 4. Sensation is felt by us due to a microscopically small current flowing to the brain.
Answer: True.
In simple words: Our nerves transmit signals as tiny electrical impulses, which are essentially small currents.

🎯 Exam Tip: This shows the biological relevance of electric currents, where small signals are crucial for bodily functions like sensation.

 

Question 5. In a car battery, a current is produced by the flow of both negatively and positively charged particles.
Answer: True.
In simple words: In a car battery's electrolyte, both positive and negative ions move to conduct electricity, while in external wires, only electrons move.

🎯 Exam Tip: Understand that current in electrolytes involves both positive and negative ion movement, unlike current in metals which is primarily electron flow.

 

Identify The Odd Term:

Question 1. Pressure exerted by a liquid, Electric current, Electric potential difference, Buoyant force.
Answer: Buoyant force. It is a vector quantity. Others are scalar quantities.
In simple words: Buoyant force has a specific direction (upwards), making it a vector, unlike the others which are scalar quantities with only magnitude.

🎯 Exam Tip: Differentiating between scalar and vector quantities is a core concept; vectors require both magnitude and direction, scalars only magnitude.

 

Question 2. Electric bulb, Electric heater, Electric bell, Electric iron.
Answer: Electric bell. Its working is based on the magnetic effect of electric current. The working of other devices is based on the heating effect of electric current.
In simple words: The electric bell uniquely uses the magnetic effect of current for its operation, whereas the others primarily rely on the heating effect to function.

🎯 Exam Tip: Categorize devices by the primary effect of electric current they utilize (heating, magnetic, chemical) to identify the odd one out.

 

Answer The Following Questions In One Sentence:

Question 1. State the relation among the Sl units of electric current, electric charge and time.
Answer: 1 ampere = 1 coulomb per second.
In simple words: This equation defines that one ampere of current means one coulomb of charge passes a point every second.

🎯 Exam Tip: This fundamental relationship (I = Q/t) is crucial for understanding current and its units.

 

Question 2. Name the positive terminal of the dry cell.
Answer: The graphite rod at the centre is the positive terminal of the dry cell.
In simple words: The central carbon (graphite) rod acts as the positive end of a dry cell.

🎯 Exam Tip: Remember the specific materials used as electrodes in common cells, like the graphite rod in a dry cell.

 

Question 3. What constitutes an electric current in a metal?
Answer: A continuous flow of electrons constitutes an electric current in a metal.
In simple words: In metals, electric current is created by the constant movement of free electrons.

🎯 Exam Tip: Understand that in metallic conductors, mobile electrons are the primary charge carriers responsible for current flow.

 

Question 4. What is a battery?
Answer: A group of two or more cells connected in series to obtain more potential difference is called a battery.
In simple words: A battery is essentially multiple individual cells joined together, typically in series, to provide a higher total voltage.

🎯 Exam Tip: Recognize that the term "battery" usually refers to a collection of cells, although sometimes a single cell is colloquially called a battery.

 

Question 5. What is a solar cell?
Answer: A solar cell is a device that converts solar energy into electrical energy.
In simple words: Solar cells convert sunlight directly into electricity through the photovoltaic effect.

🎯 Exam Tip: Understand that solar cells are key components in renewable energy systems, converting light directly into usable electrical power.

 

Question 6. State one characteristic of the Ni-Cd cell.
Answer: The Ni-Cd cell is rechargeable.
In simple words: A key feature of Nickel-Cadmium (Ni-Cd) cells is their ability to be recharged and reused multiple times.

🎯 Exam Tip: Focus on unique characteristics of different cell types; rechargeability is a major advantage of Ni-Cd cells.

 

Question 7. Give one example in which the magnetic effect of electric current is used.
Answer: The working of an electric bell is based on the magnetic effect of electric current.
In simple words: An electric bell uses an electromagnet, which operates due to the magnetic field produced by electric current, to ring.

🎯 Exam Tip: The electric bell is a classic and easy-to-understand example of the practical application of the magnetic effect of electric current.

 

Answer The Following Questions:

Question 1. When do we get current electricity?
Answer: We get current electricity when charged particles such as electrons, positive ions and negative ions are made to flow in a conductor by applying electric force.
In simple words: Current electricity is produced when charged particles are forced to move continuously through a material.

🎯 Exam Tip: Emphasize that current electricity requires a continuous flow of charge carriers, driven by an electric force or potential difference.

 

Question 2. Explain the concept of electrostatic potential (electric potential).
Answer: A liquid flows from a higher level to a lower level. Heat flows from a body at a higher temperature to a body at a lower temperature. Also when different parts of a body are at different temperatures, heat flows from the part at a higher temperature to the part at a lower temperature.
Similarly, a positive charge (free to move) flows from a point at a higher electric level to a point at a lower electric level and a negative charge (free to move) flows from a point at a lower electric level to a point at a higher electric level. The electric level deciding the direction of flow of electric charge is called electrostatic potential (electric potential).
In simple words: Electric potential is like a pressure level for charges; positive charges move from high to low potential, while negative charges move from low to high potential, driving electric current.

🎯 Exam Tip: Use analogies like water flowing downhill or heat transfer to help explain electric potential as a measure that determines the direction of charge flow.

 

Question 3. What is the Sl unit of electric potential?
Answer: The Sl unit of electric potential is the volt (V).
[Note: This unit is named in honour of Alessandro Volta (1745-1827), Italian physicist, the inventor of the electric battery.]
In simple words: The volt is the standard unit used to measure electric potential or potential difference.

🎯 Exam Tip: Knowing the SI unit (volt) and its historical context (Alessandro Volta) can enhance your answer and provide extra details.

 

Question 4. What is potential difference?
Answer: Potential difference is the difference between the potentials at two points. It is similar to the height of a waterfall or the temperature difference between a hot body and a cold body. Potential difference is expressed in volt.
In simple words: Potential difference is the work done per unit charge to move a charge between two points in an electric field, measured in volts.

🎯 Exam Tip: Explain potential difference as the "push" that causes current to flow, drawing clear analogies to make the concept relatable.

 

Try This:

Take connecting copper wires and connect the 'circuit' as shown in Fig.(a). No current is seen to flow in the bulb. Now connect in the same 'circuit' a 1.5 V dry cell available in the market as shown in Fig.(b). Now it will be realized from glowing of the bulb that a current is flowing in the circuit. Electrons in the wire flow due to the potential difference between the two ends

ℹ️ चित्र व्याख्या (Diagram Explanation): चित्र (a) एक विद्युत परिपथ को दर्शाता है जिसमें कोई विद्युत स्रोत नहीं है, इसलिए बल्ब नहीं जलता। चित्र (b) उसी परिपथ को एक 1.5V शुष्क सेल से जुड़े हुए दिखाता है, जिससे बल्ब जलता है और परिपथ में धारा प्रवाहित होती है।

In Fig.(a), there is no current as ) there is no potential difference in the absence of any cell. Current starts flowing in the circuit as soon as the potential difference is applied. The unit of potential difference in Sl system is the volt (V). We will learn about it in the next standard.

Question 5. What is electric circuit or electrical circuit?
Answer: A continuous path consisting of conducting wires, a switch or a plug key and other resistances (for example, resistance of an electric bulb) between the terminals of a cell (or a battery) along which an electric current flows is called an electric circuit.
In simple words: An electric circuit is a complete loop through which electricity can flow, made up of wires, a power source like a cell or battery, and components like a bulb or switch.

🎯 Exam Tip: Students should focus on identifying all necessary components for a complete and functional electric circuit for full marks.

Question 6. What is electric current?
Answer: Electric current is the electric charge flowing through a conductor, such as a metal wire, per unit time.
\[ I = \frac{Q}{t} \]
In simple words: Electric current is the rate at which electric charge moves past a point in a circuit. It's like the flow rate of water in a pipe.

🎯 Exam Tip: Understanding the formula \(I = Q/t\) and its units is crucial for both theoretical questions and numerical problems.

Question 7. What is one ampere?
Answer: If one coulomb of charge is passing through any cross section of a conductor in one second, the amount of current flowing through it is called one ampere. [Note: 1 ampere = 1 coulomb per second OR 1A = 1 C/s. The coulomb is named in honour of Charles Augustin de Coulomb (1736-1806), French physicist. The ampere is named in honour of Andre Ampere (1175-1836), French physicist and mathematician.]
In simple words: One ampere is the unit of electric current, defined as one coulomb of electric charge flowing past a point in one second.

🎯 Exam Tip: Remember the definition of an ampere and its relationship to coulombs and seconds, as this is a fundamental concept often tested.

Question a. How can we measure water flow emerging from a pipe? We can find it from the amount of water (litres) coming out in a specific time period. How then is the electric current measured?
Answer: Electric current, I = Q/t. In principle, if we can measure the quantity of charge (Q) flowing through a cross section of a conductor in time t, we can determine the current (i) using this formula (for a steady current). In practice, this is not done. Usually, electric current is measured using the magnetic effect of electric current. One can also use the heating effect and chemical effect of electric current for measurement of electric current.
In simple words: While electric current is defined by charge flow over time, it's practically measured using its magnetic, heating, or chemical effects, often with an ammeter that utilizes these principles.

🎯 Exam Tip: Knowing the conceptual and practical methods of measuring electric current, along with the effects it produces, is important for a comprehensive understanding.

Question 8. What is an electric cell? What is its main function?
Answer: An electric cell is a general device used to produce a uniform flow of charges in a circuit. Its main function is to maintain a constant potential difference between its two terminals.
In simple words: An electric cell is a power source that creates a continuous flow of electricity by maintaining a steady voltage (potential difference) across its ends.

🎯 Exam Tip: Focus on the primary role of an electric cell: to establish and maintain potential difference, which drives current in a circuit.

Question 9. Name ten devices in which electric cells are used.
Answer: Electric cells are used in radio sets, wall clocks, wrist watches, torches, toys, mobile phones, cars, invertors, remote controls, ships, submarines, satellites, etc.
In simple words: Electric cells are versatile power sources found in everyday items like radios, clocks, phones, and even advanced systems like cars and satellites.

🎯 Exam Tip: Be able to list several common applications of electric cells to demonstrate practical knowledge of their importance.

Question 10. Draw a neat labelled diagram to show the design of the lead-acid cell and explain its principle of working.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक लेड-एसिड सेल को दर्शाता है जिसमें दो इलेक्ट्रोड (धनात्मक PbO2 और ऋणात्मक Pb) तनु H2SO4 इलेक्ट्रोलाइट में डूबे हुए हैं। एक वोल्टमीटर टर्मिनलों के बीच 2 वोल्ट का संभावित अंतर इंगित करता है।
The lead-acid cell contains two electrodes, Pb and PbO2, dipped in dilute H2SO4. Chemical reaction between the substances in the cell produces electric charges on the electrodes. PbO2 carries a positive charge and Pb carries a negative charge. The potential difference between the electrodes is nearly 2V. If a load, such as a bulb, is connected externally between the two electrodes, an electric current flows through it. It can deliver a large current. This cell can be recharged after getting electrically discharged.
In simple words: A lead-acid cell uses lead and lead dioxide electrodes in sulfuric acid to generate electricity through chemical reactions, providing about 2V and can be recharged. Current flows when an external load is connected.

🎯 Exam Tip: For questions involving diagrams and explanations, ensure your diagram is clearly labeled and your explanation covers the materials, chemical reactions, and the flow of current. Mentioning rechargeability is also a key point.

Question 11. State applications of the lead-acid cell.
Answer: Lead-acid cells are connected in series to obtain higher potential difference. The lead-acid battery is used in cars, trucks, motorcycles and uninterrupted power supplies (UPS).
In simple words: Lead-acid cells are commonly used in vehicles like cars and trucks, and in UPS systems, often connected in series to achieve higher voltage for power.

🎯 Exam Tip: Remember the practical uses of lead-acid cells, especially in automotive applications and backup power systems, as they are real-world examples.

Question 12. What is the potential difference delivered by the Ni-Cd cell?
Answer: The potential difference delivered by the Ni-Cd cell is (about) 1.2 V. [Note: In this cell, nickel oxide is the positive electrode and cadmium is the negative electrode. It is often used as a dry cell and it can be recharged. These cells are used in some portable machines that run on electricity like a drilling machine or a gardening tool.]
In simple words: A Ni-Cd cell provides approximately 1.2 V, using nickel oxide and cadmium electrodes, is rechargeable, and powers portable devices like drilling machines.

🎯 Exam Tip: Recall the standard potential difference of a Ni-Cd cell (1.2 V) and its key feature of being rechargeable for exam questions.

Question 13. Draw a neat labelled diagram of a simple electric circuit containing a cell, an electric bulb and a plug key. What happens when the key is (i) open (ii) closed?
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक साधारण विद्युत परिपथ को दर्शाता है। इसमें एक सेल (बैटरी प्रतीक) को एक प्लग कुंजी और एक बिजली के बल्ब के साथ श्रृंखला में जोड़ा गया है। कनेक्शन चालक तारों से बने हैं, जो एक पूर्ण लूप बनाते हैं।
(i) When the key is open, there is no current in the circuit. Hence, the bulb does not glow.
(ii) When the key is closed, a current flows in the circuit. Hence, the bulb glows.
In simple words: When the key is open, the circuit is broken, and no current flows, so the bulb remains off. When the key is closed, the circuit is complete, current flows, and the bulb lights up.

🎯 Exam Tip: Understand the fundamental concept of an open vs. closed circuit and how the key controls current flow, directly impacting the bulb's glow.

ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक सेल होल्डर को दर्शाता है जिसे कई सेलों को श्रृंखला में जोड़ने के लिए डिज़ाइन किया गया है। इसमें छह सेलों के लिए स्लॉट दिखाए गए हैं, जिसमें धनात्मक और ऋणात्मक टर्मिनल एक बैटरी के लिए उच्च संभावित अंतर प्राप्त करने के लिए व्यवस्थित किए गए हैं।

Question 14. See Fig. What is the potential difference between A and B if each cell delivers a potential difference of 2V?
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र A और B बिंदुओं के बीच श्रृंखला में जुड़े चार सेलों को दर्शाता है। पहले तीन सेल धनात्मक से ऋणात्मक जुड़े हुए हैं, प्रत्येक 2V का योगदान करते हैं। चौथा सेल विपरीत ध्रुवता (ऋणात्मक से धनात्मक) में जुड़ा हुआ है, प्रभावी रूप से कुल से 2V घटाता है।
Potential difference between A and B
= 2V + 2V + (-2V) + 2V = 4V.
In simple words: By adding the voltages of cells connected in series, and subtracting for reversed polarity, the total potential difference between A and B is calculated as 4V.

🎯 Exam Tip: When calculating total potential difference in series, pay close attention to the polarity of each cell; reversed cells subtract from the total voltage.

Question a. You must have seen the car battery available in the market. It is called a battery and not a cell. Why?
Answer: In a car battery, a number of cells are connected in series to obtain more potential difference.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र श्रृंखला में जुड़े दो सेलों को दर्शाता है, जो कुल 2V का संभावित अंतर इंगित करता है। यह दर्शाता है कि उच्च वोल्टेज के लिए बैटरी बनाने के लिए कई सेल कैसे जुड़े होते हैं।
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र A और B बिंदुओं के बीच श्रृंखला और समानांतर दोनों विन्यासों में व्यवस्थित कई सेलों को दर्शाता है, जो यह दर्शाता है कि उच्च संभावित अंतर और लंबी उम्र कैसे प्राप्त की जा सकती है। पाठ के अनुसार, A और B के बीच संभावित अंतर 8V है, जो श्रृंखला में चार 2V सेलों को दर्शाता है।
Here, two identical cells are connected in parallel. The potential difference between A and B is 2V. This arrangement can be used for a longer time compared to a single cell.
Series and parallel arrangement for higher potential difference and longer life.
Here, the potential difference between A and B is 8V.
In simple words: A car battery is termed a 'battery' because it comprises multiple individual cells connected in series to achieve a greater overall potential difference, delivering more power and longer life.

🎯 Exam Tip: Distinguish between a 'cell' and a 'battery' by understanding that a battery is an arrangement of multiple cells, usually in series, to increase voltage or capacity.

Question 1. What do you observe? Keep looking at the needle and close the plug key. The bulb will light up, and you will realize that the current has started flowing.
Answer: 1. The magnetic needle is deflected.
In simple words: When current flows in the circuit, the magnetic needle moves because the current-carrying wire creates a magnetic field.

🎯 Exam Tip: This observation is key to understanding Oersted's experiment; remember that electric current produces a magnetic field.

Question 2. Does the magnetic needle change its position? Now open the plug key.
Answer: 2. Yes.
In simple words: Yes, the magnetic needle changes position, indicating a response to the magnetic field created by the current.

🎯 Exam Tip: The deflection confirms the interaction between electric current and magnetic fields, a core principle of electromagnetism.

Question 3. Does the magnetic needle come back to the original position?
Answer: 3. Yes.
In simple words: When the current is switched off, the magnetic field disappears, and the needle returns to its original position, aligning with Earth's magnetic field.

🎯 Exam Tip: The return to the original position upon circuit interruption demonstrates the transient nature of the magnetic field produced by electric current.

Question 4. What will you conclude from this experiment?
Answer: 4. The electric current produces a magnetic field around a current-carrying conductor.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एर्स्टेड के प्रयोग को दर्शाता है। इसमें एक बैटरी, एक स्विच और एक बल्ब के साथ एक साधारण परिपथ दिखाया गया है, जिसमें एक तार कंपास (चुंबकीय सुई) के ऊपर से गुजर रहा है। जब धारा प्रवाहित होती है तो कंपास की सुई विक्षेपित होती है, जो विद्युत धारा के चुंबकीय प्रभाव को प्रदर्शित करती है।
In simple words: The experiment concludes that an electric current flowing through a conductor generates a magnetic field around it, causing a nearby magnetic needle to deflect.

🎯 Exam Tip: This experiment is fundamental; remember that electricity produces magnetism, a principle discovered by Hans Christian Oersted.

Activity 2 : Will the pins/nails continue to stick when the plug key is opened?
Answer: No.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक इलेक्ट्रोमैग्नेट को दर्शाता है जो एक लोहे के पेंच के चारों ओर तांबे के तार लपेटकर बनाया गया है। एक विद्युत सेल और एक प्लग कुंजी कॉइल से श्रृंखला में जुड़े हुए हैं। जब धारा प्रवाहित होती है तो लोहे की पिनें पेंच से चिपकी हुई दिखाई जाती हैं, जो अस्थायी चुंबकत्व को दर्शाती हैं।
In simple words: No, the pins will not stick because opening the key breaks the circuit, stopping the current, and thus the electromagnet loses its magnetism.

🎯 Exam Tip: Understand that electromagnets are temporary magnets; their magnetic property exists only as long as current flows through their coil.

Question 15. What is an electromagnet? State ! its applications.
Answer: If a coil is wound around an iron screw (or an iron rod) and a current is passed through the coil with a cell (or a battery), the screw behaves as a magnet as long as there is current in the coil. The i system of the coil and the screw is called an electromagnet. It is an example of magnetic effect of electric current. Applications: Electric bell, cranes for moving heavy loads from one place to another, toys that run on electric cells.
In simple words: An electromagnet is a temporary magnet created by passing current through a coil wrapped around an iron core. It's used in devices like electric bells, cranes, and toys.

🎯 Exam Tip: Define an electromagnet based on its construction and temporary magnetic nature, and be able to list at least two common applications.

Question 16. How can the strength of an electromagnet be increased?
Answer: The strength of an electromagnet can be increased by increasing the current producing the magnetic field.
In simple words: The strength of an electromagnet can be enhanced by increasing the amount of electric current flowing through its coil.

🎯 Exam Tip: Remember the direct relationship: higher current means a stronger electromagnet. Other factors like number of turns and core material also play a role but current is often the primary adjustable factor.

Question 17. What is the use of the elastic iron strip in the electric bell?
Answer: Due to the elastic iron strip, the making and breaking of the circuit occur alternately and the bell continues to ring as long as the key in the circuit is closed.
In simple words: The elastic iron strip in an electric bell acts as an automatic switch, repeatedly making and breaking the circuit to allow the hammer to strike the gong continuously.

🎯 Exam Tip: Understand the crucial role of the elastic iron strip in an electric bell, as it enables the continuous ringing action by cyclically completing and breaking the circuit.

Question 18. What will happen if the elastic iron strip in the electric bell loses its flexibility?
Answer: When the circuit breaks and the electromagnet loses its magnetism, the strip, due to loss of flexibility, will not return to its normal position of contact with the screw. Hence, the circuit will not be completed and the bell will not ring.
In simple words: If the elastic iron strip loses flexibility, it won't spring back to complete the circuit after being attracted, preventing the electromagnet from re-energizing and the bell from ringing.

🎯 Exam Tip: This question tests the understanding of how the elastic strip's flexibility is essential for the electric bell's continuous operation. Lack of flexibility means the circuit remains open, and the bell fails.